Test 1 Flashcards

Question

Electron Microscopy (EM)

Answer 1

 Biological materials have little inherent contrast: need to be stained.  Requires negative staining with electron dense material such as Uranyl acetate, or Phosphotungstate.  Resolution range is usually 50-75 angstroms.  Detailed structural interpretation is not always possible, sometimes misleading.

Answer 2

Electron microscope

Answer 3

Allows the observation of biological specimens in their native environment (not stained or fixed in any way) at cryogenic temperatures in EM (-180°C for liquid nitrogen stages, -269°C for He). Resolution range is around 3.3-20 angstroms **NO STAINING!**

Answer 4

Cryo-Electron Microscopy (Cryo-EM)

Answer 5

1. x-ray crystallographic method 2. Electron Microscopy 3. Cryo-Electron Microscopy 4. Nuclear Magnetic Resonance (NMR)

Answer 6

X-ray Crystallographic Method

Answer 7

A RNA/ DNA genome that in enclosed in a capsid, which is surrounded by an evelope which is a bubble of fat. There are glycoproteins in the evelope.

Answer 8

the protein shell of a Virus that encases/envelopes the viral nucleic acid or genome made up of capsomeres held together by non-covalent bonds Most Viruses have one capsid, except Reoviruses which have a double layered capsid.

Answer 9

Capsid + Virus Nucleic acid (DNA or RNA)/Genome

Answer 10

the basic subunit protein in the capsid of a virus.

Answer 11

Helical Symmetry and ## Footnote Cubic/Icosahedral Symmetry

Answer 12

- In the nucleocapsids with helical symmetry, the capsomeres and nucleic acid are wound together to form a helical or spiral tube. - **Because of the interactions between the nucleic acid and capsid protein, incomplete virions (empty helical particles) cannot form.** There are Naked Helical Virus and enveloped Helical Virus. In all Animal Viruses, the Helical Nucleocapsid is enclosed within a Lipoprotein Envelope. Naked Helical Nucleocapsids are common among Plant Viruses, eg. Tobacco Mosaic Virus

Answer 13

An Icosahedron is a solid with 12 corners [vertices], 20 facets [Equilateral triangular faces], and 30 edges. - Two types of capsomers are present in the icosahedral capsid. They are the pentagonal capsomers at the vertices (pentons) and the hexagonal capsomers making up the facets (hexons). There are always 12 pentons, but the number of hexons varies with the virus group. - Seen in Spherical Viruses We also have naked icosahedral and enveloped

Answer 14

(T-number): Describes the relation between the number of pentagons and hexagons of the icosahedron. The larger the T-number the more hexagons are present relative to the pentagons. Triangulation number is calculated using the formula: Where h and k are the distances between the successive pentagons on the virus surface for each axis. Simply remember, h and K are calculated based on the number of jumps from one pentagon to adjacent pentagon across the hexamer.

Answer 15

T=h^2+ h x K+k^2 h= number of straight jumos K= number of times that you change direction

Answer 16

T=1, simplest icosahedron, the capsid consists of 60 copies of CP protein.

Answer 17

The outer capsid has a T=13 icosahedral symmetry, the inner capsid a T=2 icosahedral symmetry.

Answer 18

Virions are composed of several parts, each with separate shapes and symmetries, such as Pox Viruses. Bacterial viruses (Bacteriophage) also contain complicated structures, i.e., Icosahedral heads and helical tails.

Answer 19

 Responsible for the structural symmetry of the Virus Particle  Encases and protects the viral nucleic acid from enzymes (nucleases), chemicals and physical conditions (pH and Temperature)  Receptor attachment proteins on Viral Capsid facilitates the attachment of the Virus to Specific Receptors on the Susceptible Host cells.  Interaction with host cell membranes to form the envelope  Uncoating of the genome in host cell  Transport of the Viral Genome to the appropriate site. May dump the genome into the cytoplasm (most + ssRNA viruses), or serve as the core of replication (Reovirus and Retrovirus)  Facilitates Specific recognition and Packaging of the nucleic acid genome Capsid contains Antigenic sites. Determines the Antigenicity of the Virus

Answer 20

which is usually a lipid bilayer with embedded proteins. The envelope facilitates virus entry into host cells and may also help the virus to adapt fast and evade the host immune system. Enveloped viruses can cause persistent infections.

Answer 21

The envelope is acquired by budding of viral nucleocapsid through a cellular membrane, such as cytoplasmic membrane, golgi membrane or nucleus membrane.  Budding only occurs at the sites where the virus specific proteins have been inserted into host cell membrane.

Answer 22

occurs at the sites where the virus specific proteins have been inserted into host cell membrane.

Answer 23

1. Glycoprotein 2. Matrix protein

Answer 24

 The glycoproteins are anchored in the lipid bilayer by means of hydrophobic bonds.  These proteins have a large external domain and a small cytoplasmic domain. Theyare transmembrane proteins.  They are often the spikes seen on the virus surface.

Answer 25

**External glycoprotein** anchored in the envelope by a single transmembrane domain, and a short internal tail. These proteins are usually the major antigens of the virus and involved in functions such as hemagglutination, receptor binding, antigenicity, and membrane fusion. Example, Hemagglutinin (HA) and Neuraminidase (NP) in Influenza Virus. **Channel proteins,** which are mostly hydrophobic proteins that form a protein lined channel through the envelope. This protein alters permeability of the membrane ( e.g. ion channel). Such proteins are important in modifying the internal environment of the virus.

Answer 26

Release progeny virus from host cell, Antigenic

Answer 27

Binding, Fusion, Antigenic, Hemagglutination

Answer 28

Glycoprotein; fuses lipid envelope of the virus, and then releases viral proteins into the cytoplasm pH independent fusion proteins, such as in HIV and Measles and pH dependent (Acidic) fusion proteins, such as HA in influenza virus

Answer 29

 These proteins link the internal nucleocapsid to the lipid membrane envelope.  Play a crucial role in Virus Assembly  Allow stabilization of the lipid envelope  Interact with the RNP (ribonucleoprotein) complex as well as with the viral membrane. Serves as the recognition site of nucleocapsid at the plasma membrane and mediates the encapsidation of the RNA-nucleoprotein cores into the membrane envelope.  May perform other regulatory functions during virus replication.

Answer 30

1. Directly 2. Via a matrix protein 3. via a muliprotein layer

Answer 31

 Acquired from a cellular membrane of host cell, such as cytoplasmic membrane.  Maintained only in Aqueous or Moist Environments. The Lipid envelope is sensitive to Desiccation, Heat, and alteration of pH.  Enveloped viruses can be inactivated by the dissolution of lipid membrane with lipid solvents such as: Ether Chloroform Sodium deoxycholate, Detergents, etc. **Therefore, enveloped viruses are easy to sterilize than non-enveloped viruses and cannot survive for longer periods in environment.**

Answer 32

Can be RNA(double or single stranded) or DNA (double or single stranded) DNA can be linear or circular RNA- + sense( can be translated into protein right away) or negative sense- noninfectious genome RNA can be Non-Segmented Genome (Monopartite) or Segmented Genome (Multipartite)

Answer 33

is similar to mRNA and thus can be immediately translated by the host cell.

Answer 34

is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation.

Answer 35

Outcomes:  Most cases minor changes.  Virus may become resistant to Antiviral drugs.  May cause change in antigenicity. Detrimental effect on

Answer 36

no change in the nucelo tide, but a base pair is different

Answer 37

A STOP codon is created, which inhibits virus sythesis

Answer 38

Conservative- change in the nucleotide doesn't change the amino acid Non-Conservative- change in the nucleotide changes the amino acid

Answer 39

Intramolecular recombination involves the exchange of nucleotide sequences between different, but usually closely related, viruses during replication.

Answer 40

Reassortment is the most important mechanism for high genetic diversity in Viruses with segmented genome **usually only occurs with segemented viruses**

Answer 41

For the double-stranded DNA viruses, the complexity ranges from the relatively simple circular super-coiled genome of the Polyomaviridae and Papillomaviridae (5– 8 kbp) to the linear Herpesvirinae (125–235 kbp)  The single-stranded DNA viral genomes are either linear (Parvoviridae) or circular (Circoviridae and Anellovirus), with sizes ranging from 2.8 to 5 kbp

Answer 42

The size of animal RNA viral genomes ranges from less than 2 kb (Deltavirus) to more than 30 kb for the largest RNA viruses (Coronaviridae)

Answer 43

 Constitute up to 50-70% of the Virion.  The genomes of animal viruses encode from as few as one protein to more than 100.  Virion proteins fall into two general classes: modified proteins and unmodified proteins.

Answer 44

 Enzymes  Structural proteins  Viral Nonstructural Proteins  Regulatory proteins  Inhibitors

Answer 45

Enzymes required for mRNA transcription Enzymes required for nucleic acid replication Reverse transcriptase, etc.

Answer 46

Hydrolytic enzymes produced by bacteriophages to cleave the host's cell wall.

Answer 47

Enzyme produced by a retrovirus (such as HIV) that enables its genetic material to be integrated into the DNA of the infected cell

Answer 48

Enzyme used to generate complementary DNA (cDNA) from a RNA template.

Answer 49

Viral Genome Replication.

Answer 50

Enzymes that cleave glycosidic bonds. Allows release of viruses from host cell.

Answer 51

The proteins that form the Viral Capsid. Such as VP7 and VP4 proteins of Rotaviruses

Answer 52

Proteins encoded by a viral genome that are produced in the organisms they infect, but not packaged into the virus particles. Some of these proteins may play roles within the infected cell during virus replication or act in regulation of virus replication or virus assembly. For example, NSP1-NSP5 genes of Rotavirus. **These are never in a viron**

Answer 53

A broad category of viral proteins that play indirect roles in the biological processes and activities of viruses. Included here are proteins that either regulate the expression of viral genes or are involved in modifying host cell functions. Many of the proteins in this category serve multiple functions. For example, products of the retroviral NEF GENE. ## Footnote **imporant for immune response**

Answer 54

Virion without Nucleic Acid [Empty Capsid]

Answer 55

A virus that cannot replicate because it lacks a full complement/ copy of viral genes. Defective viral particles result from mutations or errors in the production or assembly of virions.

Answer 56

Replication of Defective Virions occurs only in mixed infection with a helper virus. Helper virus can supplement the genetic deficiency and make defective viruses replicate progeny virions when they simultaneously infect host cell with defective viruses.

Answer 57

When the defective viruses can not replicate, but can interfere other congeneric mature virion entering the cells, we call them defective interfering particles (DIP).

Answer 58

Contains non-viral genome within the viral capsid, such as **host** nucleic acid instead of viral nucleic acid. Look like ordinary Viral particles under electron microscope, but do not replicate. Synthetic Viral particles (Pseudovirions) are being used to inject foreign nucleic acid into a cell, such as delivery of DNA Vaccines. **viruses have the host genome, not the viral genome**

Answer 59

When related viruses infect the same cell, the genome of one virus may be enclosed in the heterologous capsid of the second virus

Answer 60

1. stability 2. population size 3. Host range 4. Persistent Infections 5. Avoid Exposure to the outside enviornment

Answer 61

affects its survival in the environment: Example: Viruses that are transmitted by the respiratory route have low environmental stability, whereas those transmitted by the fecal–oral route have a higher stability.

Answer 62

A virus may disappear from a population if supply of susceptible hosts is exhausted. This depends on size of population, immunity and pattern of virus shedding.

Answer 63

Many viruses can infect more than one host. Example, Foot and Mouth Disease Virus and Rotavirus.

Answer 64

Virus remains in host for long periods

Answer 65

Vertical Transmission, Venereal Transmission, Vector Transmission

Answer 66

Viruses depend on 3 factors: 1. host factor 2. Enviornment 3. Pathogen **All of these factors contribute to the developement of a disease.**

Answer 67

Vegetation, Deforestation, Natural Calamities  Overcrowding, poor ventilation, housing  Stress factors, diet  Level of hygiene  Vector & Reservoir Populations

Answer 68

Evolution/Selection Pressure  Mechanisms of Genetic Diversity  Transmission Efficiency  Portal of entry of Virus in Host  Tropism to Host Organs  Dose of Infection  Immuno evasion

Answer 69

Host Species  Host Immunity  Expression of Critical Receptors  Host Physiological factors (Nutrition status, Age, Hormonal Factors, Stage of Cell Differentiation)  Interferons, Other Inhibitors  Fever

Answer 70

With globalization, the study of Viral diseases has become more complex. The transmission dynamics of zoonotic pathogens are now influenced by several anthropogenic factors, such as human travel, trade of animals and other resources, deforestation, development and land use, and human demographics and behavior.

Answer 71

is a form of immunity that occurs when the vaccination of a significant portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity.

Answer 72

refers to the interval between infection and the onset of clinical signs. In many diseases there is a period during which animals are infectious before they become sick.

Answer 73

The first signs and feelings of illness after incubation period. The period of early symptoms of a disease occurring after the incubation period and just before the appearance of the characteristic symptoms of the disease.

Answer 74

When the disease is at its height. Severe clinical signs.

Answer 75

Period when clinical signs begin to subside

Answer 76

The body gradually returns to its pre-diseased state, and health is restored.

Answer 77

Risk Group 1: no to low individual to community risk i.e. AAV Risk Group 2: moderate individual risk; low community risk i.e. herpes, foot and mouth disease, adenoviruses Risk Group 3: high individual risk, low community risk i.e. HIV, Hep. B, yellow fever Risk Group 4: high individual risk and high community risk i.e. Ebola, smallpox **Treatment is not known/ hard to get for risk 4 pathogens**

Answer 78

based on the risk group(s) of pathogens it handles. Ross has a BSL- 2 lab

Answer 79

BSL-4 is the maximum containment laboratory. BSL-4 labs handle dangerous and exotic pathogens belonging to the highest risk group, i.e. risk group 4 (e.g. Ebola virus).  Lab workers should wear a one-piece, positively air-pressurized, HEPA-filtered, supplied- air suit.  Negative air-pressure must be maintained in the laboratory room.  Incoming and outgoing air should be HEPA-filtered (HEPA: High Efficiency Particulate Air)  Sterilization through double door autoclaving system  Suit decontamination shower after leaving the containment laboratory area.

Answer 80

Biological substances that pose a threat to the health of living organisms, primarily that of humans

Answer 81

Laboratory biosafety describes the containment principles, technologies and practices that are implemented to prevent the unintentional exposure to pathogens and toxins, or their accidental release.

Answer 82

Very small droplets of fluid that can spread via air. Viruses can spread in lab through aerosol route.

Answer 83

An enclosed, ventilated laboratory workspace for safely working with materials contaminated with (or potentially contaminated with) pathogens requiring a defined biosafety level.

Answer 84

Laboratory biosecurity describes the protection, control and accountability for valuable biological materials (VBM, see definition below) within laboratories, in order to prevent their unauthorized access, loss, theft, misuse, diversion or intentional release.

Answer 85

 Collection of the sample from the right site  At the right time  And from the most appropriate animal  Proper Transport and Storage of Sample  Performing the correct diagnostic test  Proper interpretation of results

Answer 86

 Epidemiological data  Case histories  Clinical signs

Answer 87

specimens should be collected as soon after onset of symptoms as possible, because maximal amounts (titers) of virus are usually present at the onset of signs . The chance of viral recovery is best during the first three days after onset and is greatly reduced beyond 5 days with many viruses.

Answer 88

For serological tests, two blood specimens are generally collected – one during the acute phase of the illness and the second sample during the convalescence period (varies upon type of virus, 10-14 days after 1st sample or even more). Can have a positive test with one titer due to exposure! This is why you MUST take 2!

Answer 89

As a general rule, specimens collected for molecular diagnostics, such as PCR, should be obtained during the early part of the illness.

Answer 90

The site from which the specimen is collected will be influenced by the clinical signs and knowledge of the pathogenesis of the suspected virus.

Answer 91

All specimens should be delivered to the laboratory as soon after collection as possible, since a loss of infectivity occurs over time.

Answer 92

Because of the lability of many viruses, specimens intended for virus isolation must always be kept cold and moist

Answer 93

If immediate delivery is not possible, refrigerate specimens (2 °C to 8 °C), or place them on wet ice or a cold pack.

Answer 94

Avoid freezing. But, if samples must be frozen, freeze them rapidly at –20 °C or –70 °C.

Answer 95

Specimens for histopathologic examination should never be frozen. They should be fixed in 10% buffered formalin or fixatives.

Answer 96

Stabilize the infectivity of specimens, especially swabs. VTM prevents specimen from drying, helps maintain viral viability and retards the growth of microbial contaminants.  The VTMs consist of a buffered salt solution to which has been added protein (e.g., gelatin, albumin, or fetal bovine serum) to protect the virus against inactivation and antimicrobials to prevent the multiplication of bacteria and fungi. **We don't want the swabs to get dry.**

Answer 97

(1) breakage of containers resulting in spillage, (2) Resulting in exposure to possible infection, and (3) A delay in package delivery to the diagnostic laboratory, which may have serious implications during an outbreak situation.

Answer 98

To prevent spillage, it is recommended to follow the basic triple packaging system while transporting infectious materials.

Answer 99

Finely minced and homogenized in a glass or mechanical homogenizer. Homogenates are diluted in 1:10 and centrifuged at 10,000 g for 15 minutes Tools: Mortar and pestle or Ten Broeck Tissue Grinder

Answer 100

Use a vortex mixer: Phosphate buffer saline or water is added to liquefy the fecal, if pasty or solid. Then vortexed and centrifuged, supernatant collected.

Answer 101

Twirl the swab in VTM and vortex the VTM in the vial.

Answer 102

1. Clinical Signs 2. necropsy 3. Histopathology

Answer 103

Turkey egg-shaped Kidney

Answer 104

Cyanosis of tongue, appears purplish, blue

Answer 105

Negri body or inclusion bodies in an infected neuron

Answer 106

Cultivation/ isolation of viruses in cells/tissue culture and inovulation in eggs

Answer 107

refers to damage or morphological changes to host cells during virus invasion.

Answer 108

Can be used to demonstrate viruses in samples and detect viruses that cannot be grown in in-vitro

Answer 109

The virus sample is mixed with a solution of heavy metal salt that is highly opaque to electrons (sodium phosphotungstate or uranyl acetate).  The mixture is then spread on a thin layer on a carbon-coated copper grid and dried.

Answer 110

 Following bombardment with an electron beam, the stain absorbs electrons in much higher amounts than the sample.  On the other hand, the parts of the viral particles that are not penetrated by the stain appear as electron-lucent (low affinity, less electron density) areas on an opaque (high affinity, electron-dense) background.

Answer 111

approximately 106 -107 virions per ml.

Answer 112

The method used in TEM is based on transmitted electrons.  TEM seeks to see what is inside or beyond the surface.

Answer 113

The method used in SEM is based on scattered electrons.  SEM focuses on the sample’s surface and its composition.

Answer 114

Qualitative or quantitative measurement of a target entity/analyte, such as a drug or biomolecule.

Answer 115

A diagnostic test that is considered to be the most accurate and best available under a particular condition or set of conditions.

Answer 116

The probability that a negative test result accurately indicates the absence of infection.

Answer 117

The probability of a positive result accurately indicating the presence of infection.

Answer 118

The probability (percentage) that cases with the infection (determined by the result of the reference or ‘gold standard’ test) will have a positive result using the test under evaluation.

Answer 119

The probability (percentage) that cases without the infection (determined by the result of the reference or ‘gold standard’ test) will have a negative result using the test under evaluation.

Answer 120

The clear yellowish fluid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot.  The clot is removed by centrifugation and the resulting supernatant, designated serum, is carefully removed using a Pasteur pipette.

Answer 121

Red-top Vacutainer Tube

Answer 122

is produced when whole blood is collected in tubes that are treated with an anticoagulant. The blood does not clot in the plasma tube. The cells are then removed by centrifugation. The supernatant, designated plasma is carefully removed from the cell pellet using a Pasteur pipette.

Answer 123

Plasma – clotting factors = Serum

Answer 124

Lavender-top EDTA Vacutainer Tube

Answer 125

 Typical ELISA: Antigen coated in a well Add antibody tagged with an Enzyme Antigen binds to enzyme-tagged antibody Wash the excess unbound antibodies Add substrate Enzyme tagged to antibody which is bound to antigen will change color of substrate. Intensity of color indicates more positive reaction.

Answer 126

Antigens are immobilized and enzyme-conjugated primary antibodies are used to detect or quantify antigen concentration. The specificity of the primary antibody is very important.

Answer 127

Primary antibodies are not labeled, but detected instead with enzyme- conjugated secondary antibodies that recognize the primary antibodies.

Answer 128

The antigen to be measured is bound between a layer of capture antibodies and a layer of detection antibodies. The two antibodies must be very critically chosen to prevent cross-reactivity or competition of binding sites.

Answer 129

The antigen of interest from the sample and purified immobilized antigen compete for binding to the capture antibody. A decrease in signal when compared to assay wells with purified antigen alone indicates the presence of antigens in the sample. Unlabeled antibody is incubated in the presence of its antigen (sample). These bound antibody/antigen complexes are then added to an antigen-coated well. 1. The plate is washed, so unbound antibody is removed. (The more antigen in the sample, the more Ag-Ab complexes are formed and so there are less unbound antibodies available to bind to the antigen in the well, hence "competition".) 2. The secondary antibody, specific to the primary antibody, is added. This second antibody is coupled to the enzyme. 3. A substrate is added, and remaining enzymes elicit a chromogenic or fluorescent signal. 4. The reaction is stopped to prevent eventual saturation of the signal. 5. Weaker signal indicates presence of antigens in sample.

Answer 130

The antibodies are labelled with a fluorescent dye (most commonly used is fluorescein isothiocyanate [FITC] or rhodamine). Visible fluorescence appears following antigen- antibody reaction.

Answer 131

Labelled antibodies are added onto the sample (Antigen). Visible fluorescence appears at the binding sites of the specific antibodies (antigen-antibody binding).

Answer 132

IFAT employs a secondary antibody labeled with a fluorescent marker that recognizes the primary antibody bound to antigen.

Answer 133

The antibody is tagged with a enzyme, generally horseradish peroxidase. The enzyme reacts with a substrate to produce a colored product that can be visualized in the infected cells with a standard light microscope.

Answer 134

Enzyme tagged with primary antibody that binds to antigen. Upon successful antigen-antibody binding, tagged enzyme catalyzes substrate to produce color product.

Answer 135

Enzyme tagged to a secondary antibody that is specific against primary antibody.

Answer 136

A form of POC (Point-of-Care) test that is simple to perform, easy to carry, and does not require specialized equipment. i.e. pregnacy tests

Answer 137

Diagnostic testing performed at or near the patient’s site of care.

Answer 138

 One of the antibodies is immobilized on the chromatographic paper, and the other is labeled with colloidal gold and infiltrated into sample pad.  When the liquid sample is dropped on the sample pad, the antigen in the sample forms an immunocomplex with the antibody labeled with colloidal gold.  Its complex moves along with the liquid sample in the nitrocellulose membrane, and makes a contact with the antibody immobilized on the membrane, followed by forming an immuno- complex with the immobilized antibody, resulting in generating a colored red purple line.  Appearance of this red purple line on the membrane indicates the presence of antigen of interest in the sample.  The excess unbound colloidal gold labeled antibodies migrate further forward and bind to antibodies in membrane against these antibodies, also yielding test control band.

Answer 139

Agglutination is a method using the property of specific antibodies to bind many antigens (antigens on pathogen, or antigen coated particles- latex beads) into single clumps thereby forming large complexes, which are easily precipitated. The precipitation can be macroscopically or microscopically visible.

Answer 140

Disease caused by same virus, but known by different names in different parts of the world. Example, Hog Cholera in North America is known as Classical Swine Fever in rest of the world. Both are same disease caused by members of genus Pestivirus. However, the Disease linked Nomenclature/Naming of Viruses may cause Confusion Different Viral Diseases, but known by the same name. Example, Hand-Foot and Mouth Disease in Humans is different from Foot and Mouth Disease of Livestock. The former being caused by members of genus Enterovirus, whilst later being caused by members of genus Aphthovirus.

Answer 141

 Baltimore classification (first defined in 1971) is a classification system based on Viral Genome.  Using this system, viruses are classified into one of the seven groups depending on a combination of their nucleic acid (DNA or RNA), strandness (single-stranded or double- stranded), Sense, and method of replication.

Answer 142

The International Committee on Taxonomy of Viruses (ICTV) Classification System is followed by Virologists Worldwide The ICTV is the only body charged by the International Union of Microbiological Societies with the task of developing, refining, and maintaining a universal virus taxonomy.  Established in 1966.  Considers the following for Classification of Viruses:  Nature of Virus Genome and Virus Genetic Diversity  Virus Replication Strategies  Virus Morphology

Answer 143

Order: Herpesvirales Family: Herpesviridae Subfamily: Alphaherpesvirinae Genus: Simplexvirus Species: Herpes simplex virus 1 (HSV-1) Herpes simplex virus 2 (HSV-2)

Answer 144

An abnormal structure in a cell nucleus or cytoplasm, such as aggregates of proteins, having characteristic staining properties and associated especially with certain viral infections Found in Nucleus or Cytoplasm, or for some viruses in both

Answer 145

can be translated into a protein

Answer 146

Can't be translated into the genome

Answer 147

Viruses do not have the genetic capability to multiply by division. Outside the host cell, they are inert/dormant particles. Viruses need a Living Host Cell to Replicate and Generate Next Progeny of Viruses. Inside the host cell, the virus hijacks and utilizes the host cell machinery to produce its proteins and nucleic acid for the next generation of virus.

Answer 148

1. Cell/Tissue Culture 2. Inoculation in Embryonated Egg 3. Laboratory Animals

Answer 149

 Parts of an organ or a whole organ are cultured in-vitro.  New Technique. Technical difficulties

Answer 150

 Cell culture refers to the removal of cells from an animal or plant and their subsequent growth in a favorable artificial environment.  Cell culture involves the growth of dispersed cells in-vitro, either as cells in suspension, or as a monolayer on a solid surface such as a inner surface of polystyrene culture flask.

Answer 151

Cells which do not require attachment for growth or do not attach to the surface of the culture vessels. Can be propagated in suspension.

Answer 152

When the bottom of the culture vessel is covered with a continuous layer of cells, usually one cell in thickness, they are referred to as monolayer cultures.

Answer 153

 This is the maintenance of growth of cells dissociated directly from the parental tissue (such as kidney or liver) of human or animal origin.  Cells have the same chromosomes and same number of chromosomes as the original tissue. **They are morphologically similar to cells of parent tissue** Monolayer

Answer 154

**Advantages:**  Best culture systems for isolation and propagation of viruses.  Heterogeneous – many cell types  Closest to animal (Similar to Animal Tissue cells)  Used in producing Viral Vaccines **Disadvantages::**  Difficult to obtain  Relatively short lifespan in culture [Capable of only 5-20 subcultures]  Very susceptible to contamination  May not fully act like parent tissue due to complexity of culture media

Answer 155

 When a primary culture is sub-cultured, it becomes known as secondary culture or cell line.  Subculture (or passage) refers to the transfer of cells from one culture vessel to another culture vessel.  This is periodically required to provide fresh nutrients and growing space for continuously growing cell lines. **You grow the cells on two plates.**

Answer 156

After the first subculture, the primary culture becomes a cell line

Answer 157

The cell lines which have a limited life span and go through a limited number of cell generations.  Homogenous population of a single cell type – fewer cell types  Limited life span: May be sub-cultured up to 100 times before the cells die  Derived mainly from embryos; or from secondary cell cultures  Cell retains original morphology and diploid chromosome number  These cell lines exhibit the property of contact inhibition, density limitation and anchorage dependence  The growth rate is slow and doubling time is around 24-96 hours  Technically, less hassle to use

Answer 158

Acquire the ability to divide indefinitely. **Continuous cell lines/Immortal Cell Lines/Heteroploid Cell Lines –**  Cell cultures of a single cell type - Most homogeneous  Derived directly from cancer cells; or induced transformation of a primary or diploid cell strain to divide indefinitely  Genetically weird – furthest from animal. Abnormal morphology & chromosome number  Absence of contact inhibition and anchorage dependence  The growth rate is rapid and doubling time can be 12-24 hours  Hassle free to use  FDA prohibits their use in Vaccine Production **HeLa Cells- Example**

Answer 159

(or fibroblast-like) cells are bipolar or multipolar, have elongated shapes, and grow attached to a substrate.

Answer 160

cells are polygonal in shape with more regular dimensions, and grow attached to a substrate in discrete patches.

Answer 161

is a growth mechanism which functions to keep cells growing into a layer one cell thick (a monolayer). If a cell has plenty of free space, it replicates rapidly and moves freely.

Answer 162

cells are polygonal in shape with more regular dimensions, and grow attached to a substrate in discrete patches.

Answer 163

cells are spherical in shape and usually grown in suspension without attaching to a surface. float, detached

Answer 164

Provides all the necessary nutrients (amino acids, inorganic salts, Vitamins and Glucose) required for growth of Cells i.e. Eagle’s Basal Medium, Leibovitz L-15 Medium

Answer 165

 Vital source of adhesion factors, attachment and spreading factors, low molecular weight nutrients, and hormones and growth factors.  Carrier proteins for lipoid substances and trace elements into the cell  Regulate cell membrane permeability  The most widely used animal serum supplement is fetal bovine serum, FBS.

Answer 166

5-10 % serum

Answer 167

0-2 % serum

Answer 168

Phenol red pH Indicator red- acidic orange- alkaline

Answer 169

CONTAIMINATION! it will turn orange

Answer 170

 The growth medium controls the pH of the culture and buffers the cells in culture against changes in the pH  Usually, this buffering is achieved by including an organic (e.g., HEPES) or CO2-bicarbonate based buffer.  Changes in the atmospheric CO2 can alter the pH of the medium.  Therefore, it is necessary to use exogenous CO2 when using media buffered with a CO2-bicarbonate based buffer  4 – 10% CO2 is common for most cell culture experiments.

Answer 171

To prevent contamination with bacteria, mycoplasma, yeast, molds, etc.

Answer 172

Cell line and Temperature Human and Mammals- 36-37 Insect Cells- 27 Avian Cell lines- 38.5 Cold- blooded animals- 15-26

Answer 173

Trypsin and Collagenase

Answer 174

transfering cell into a new medium plate Treat primary cell culture with Trypsin and EDTA, which releases the cells.

Answer 175

Incubating cells with too high a trypsin concentration for too long a time period will damage cell membranes and kill the cells. Therefore, researchers now often use enzyme-free dissociation buffers to maintain integrity of cells.

Answer 176

1. Polystyrene Flasks 2. Polystyrene Dishes 3. Microwell Plates 4. Roller Bottles 5. Leighton Tube

Answer 177

You can check using an inverted Tissue Culture Microscope

Answer 178

(abbreviated CPE) refers to damage or morphological changes to host cells during virus invasion.

Answer 179

Shell Vial: Small borosilicate glass vial with a coverslip **grow the cells on a coverslip**

Answer 180

* Single monolayer consisting of multiple [different] cell types * Ideal for the isolation of multiple viruses • Detection of viral antigens Detected using a pool of fluorescein-labeled monoclonal antibodies

Answer 181

is a mixed monolayer of mink lung cells (strain Mv1Lu) and human Adenocarcinoma cells (strain A549). In combination, these cells support the detection of many viruses, in particular those of the respiratory group that includes Influenza A and B, RSV, Adenovirus, and Parainfluenza viruses 1,2, and 3. **Co-cultured cells**

Answer 182

Specific-Pathogen-Free (SPF) Eggs Egg Candler Betadine Sterile Swabs Drill Micro Drill Bits

Answer 183

7-13 year old eggs

Answer 184

9-12 days old

Answer 185

* Death of the embryo * Paralysis [sluggish movement] * Stunted growth * Urate deposits in the mesonephros • Hemorrhage and congestion * Hemagglutins in embryonic fluids * Extracellular membrane lesions Pocks on Chorioallantoic Membrane (CAM)- Pocks formed by vaccinia virus on CAM

Answer 186

Intracerebral or Intraperitoneal Mouse Inoculation

Answer 187

Ultracentrifuges have played a vital role in virology because they provide sufficient gravitational force (0,000 RPM and 200,000 x g to 150,000 RPM and 1,000,000 x g) to efficiently sediment even the smallest viruses. **very high centrifugucation**

Answer 188

**-Type of ultracentrifucation** Sample is layered as a narrow zone on the top of a density gradient, such as Sucrose of different densities. **Under centrifugal force, particles move at different rates depending on their mass.** **particles that are light will settle down slower and vise versa**

Answer 189

 Buoyant Density: If the object has exactly the same density as the fluid, then its buoyancy equals its weight. It will remain submerged in the fluid, but it will neither sink nor float.  Isopycnic Point: The point where the buoyant density of as particle equals that of the surrounding Density Gradient Medium.  Suitable Density Gradient Medium:  Sucrose In isopycnic separation, also called buoyant or equilibrium separation, particles are separated solely on the basis of their buoyant density. By this method, the particles will never sediment to the bottom of the tube, no matter how long the centrifugation time. Starting with a uniform mixture of sample and density gradient under centrifugal force, particles move until their density is the same as the surrounding medium (Isopycnic Point).  Cesium chloride

Answer 190

 Chromatographic membranes are now utilized in purification of viruses and virus like particles and for impurity removal. The macroporous structure of the membrane allows large viruses to enter it and to bind to the inner pore surface easily.  Binding of the viruses on ion exchange membranes depends on charge distribution on the virus. Adsorption and subsequent elution of viruses can be achieved by anion or cation exchange membranes.

Answer 191

counts the number of viruses in a specific volume to determine the virus concentration.

Answer 192

is lowest concentration of virus that still infects cells. Also defined as the number of infectious units per ml of the sample.

Answer 193

 Biological: Depend on a virus particle initiating a successful replication cycle.  Plaque assays  Pock assays  Various endpoint titration methods  Physical: Do not depend on any biological activity of the virus particle.  Electron microscopic particle counts  Hemagglutination  Immunological assays, such as ELISA  Quantitative PCR assays  Flow Cytometry

Answer 194

The most direct method to determine the concentration of virus particles in a sample. Not routinely carried out as:  Expensive  Required Trained Staff  Cannot assess biological activity of the preparation  Compared with a known concentration of a standard particle  Ideal for viruses with unique geometrical shapes.  Chances of error high.

Answer 195

The technology behind the Virus Counter 2100 is based on a specialized version of flow cytometry developed specifically for use with nanometer scale particles.  When using a Virus Counter, each sample is stained with two different fluorescent dyes, one specific for nucleic acid, and the other specific for protein, and analyzed as they flow through a laser beam.  This dual channel system measures intact virions through detection of co-localized protein and nucleic acids.

Answer 196

adding viruses, causes the RBC to clump If there is no hemmagglutination, then the RBC settle down at the bottom of the tube and form a button

Answer 197

The inverse of the greatest dilution that completely agglutinates the red blood cells is defined as the “HA titer” of the virus suspension.

Answer 198

The concentrations of specific viral antigens may be quantified through UV (Ultra Violet) analysis of fractions generated during HPLC..

Answer 199

Radial diffusion of purified viral antigens (standards) and viral particles through agarose gel seeded with polyclonal antisera against a viral antigen

Answer 200

Utilizes polymerase chain reaction chemistry to amplify viral DNA or RNA to produce high enough concentrations for detection and quantification by fluorescence. Fluorescent probes are used in a conventional PCR system. **helps to guessestimate viral concentrations**

Answer 201

Monolayer Plaque Assay Plaque: A circular zone of necrotic cells surrounded by viable cells in a monolayer.  The assay is elegantly simple and is the most accurate of the quantitative biological assays.  Only viruses that cause visible cell damage of cultured cells can be quantitated using this assay. It is a functional measurement, and has no relation to actual number of viruses.  Unit: Plaque-forming Units/ml (PFU) Measures the number of virus particles capable of forming plaques per unit volume. For example, if a solution has a PFU of 1000 pfu/ml, then every ml of solution contains enough virus to form 1000 plaques.

Answer 202

Each plaque respresents cel lysis initiated by one viral particle(agar restricts movement so that virus can infect only contiguous cells)

Answer 203

Crystal Violet Plaques- clear circles Viable cells- bluish purple

Answer 204

Average plaque count x reciprocal of the dilution selected • Titer: PFU/ml

Answer 205

• Pock Necrotic area on chorioallantoic membrane [CAM] of embryonated egg * Titration of herpesviruses and pox- viruses * Unit: Pock-forming units/ml CAM inoculation **pock forming units correspond to the titer of the virus**

Answer 206

• Quantitative determination of titers of oncogenic viruses Oncogenic viruses transform cells in culture * Transformed cells lose contact in- hibition and become heaped upon one another * Unit: Focus-forming units/ml

Answer 207

Loss of contact inhibition **Instead of a mono-layer, you get clumps of cells!**

Answer 208

Measures the presence or absence of infection Used for certain viruses that do not form plaques or for determining the virulence of a virus in animals or eggs • Endpoint Virus dilution that affects 50% of the test subjects * Tissue Culture Infectivity Dose50 • Lethal Dose50 * Embryo Lethal Dose50 * Paralytic Dose50

Answer 209

50% of the lab animals die

Answer 210

TCID50 is the tissue culture infectious dose which will infect 50% of the cell monolayers challenged with the defined inoculum.

Answer 211

Multiplicity of infection (moi) is the average number of virus particles infecting each cell.

Answer 212

Adding this proportional factor to the dilution next above 50% 10-2.3 A virus suspension with dilution 10-2.3 represents 1 TCID50/0.1ml, i.e. at such dilution 50% of cultures inoculated will become infected. Titer is 102.3 TCID50/0.1ml

Answer 213

 Viruses do not have the genetic capability to multiply by division.  Virus hijacks and utilizes the host cell machinery to produce its proteins and nucleic acid for the next generation of virus.  The process of Virus replication in the host cell resembles an assembly line.

Answer 214

A cell in which a virus is able to replicate, i.e. the cell machinery supports replication of the virus.

Answer 215

Cells in which a factor or factors necessary to viral reproduction is not present or one detrimental to viral reproduction is present. eg. Absence of appropriate receptors.

Answer 216

Refers to the number of virions that are added per cell during infection

Answer 217

* Let us infect monolayer cell cultures with a virus * Perform sequential sampling of virus at different time intervals • Examine the Virus titer by measuring: PFU/ml of intracellular virions and extracellular virions 1. You have a monolayer, which you add the viral suspension to. 2. Allow ~1 hr for virus to adsorb in cells. Culture cells 3. Collect aliquots of Cells and Cell-Culture fluid at different time intervals for measuring titer of intracellular and extracellular virions Burst size: Number of Virions released. Height of curve = Burst size

Answer 218

During this period, virus attaches to and enters cells, and the titer of free virus in the medium may actually decline.

Answer 219

Time interval between uncoating [“disappearance” of viruses] and appearance, intracellularly, of first infectious progeny virions.  No infectious virus can be detected during this time.  Usually ranges from 2-12 hours for most virus families.

Answer 220

The time before new infectious virus appears in the medium, i.e. time from uncoating to just prior to the release of the first extracellular virions. During this phase no extracellular virions are detected.

Answer 221

Number of infectious virions released per average cell.

Answer 222

1. Attachment- very specific lock and key reaction 2. Penetration 3. Uncoating- open it's protein capsid 4. Synthesis of Viral Components (Nucleic acid and Protein) 5. Assembly and Maturation 6. Release in large numbers

Answer 223

_Receptor:_ In cell biology, a structure on the surface of a cell (or inside a cell) that selectively receives and binds a specific substance, and mediates its entry or action into the cell. Receptors may be proteins, carbohydrates, glycoproteins, lipids, lipoproteins, or even complexes. **1. Attachment to Host Cell Surface** - Mediated by interactions between the Virus and Complimentary Receptor on Host Cell surface. Cell that lack the appropriate receptor escape being infected by viruses. - In some cases, binding to a cellular receptor is not sufficient for infection: an additional cell surface molecule, or **co-receptor,** is required for entry. - Some Viruses may use more than one host cell receptor, such as HIV. - Host cells certainly do not maintain receptors specifically for viruses, these cellular receptors carry out normal functions for cell, such as uptake of proteins. Viruses have evolved to use this receptors.

Answer 224

In some cases, binding to a cellular receptor is not sufficient for infection. An additional cell surface molecule, or co-receptor, is required for entry.

Answer 225

{Endo (within) cytosis (cell) } is a process in which a substance gains entry into a cell without passing through the cell membrane. The process involves invagination and pinching off of small regions of the cell membrane, resulting in the nonspecific internalization of molecules .

Answer 226

1. Endocytosis 2. Surface Fusion 3. Pore- Mediated Penetration 4. Antibody- Mediated Pentration

Answer 227

Used by: * Naked viruses * Most enveloped viruses Clathrin-mediated endocytosis

Answer 228

Look in powerpoint- Virus Replication

Answer 229

In Most Non-Enveloped Viruses: Lysis occurs when a viral capsid induces rupture of endosomal membrane, releasing Viral Capsid or genome.

Answer 230

In Some Non-Enveloped Viruses: Some non-enveloped viruses induce local permeabilization of host endosomal membrane to allow virus capsid penetration into the cytoplasm.

Answer 231

 Caveolin-mediated endocytosis of virus by host. (specialized lipid rafts)  Clathrin- and caveolin-independent endocytosis of virus by host.

Answer 232

Only Enveloped Viruses Viral glycoproteins are retained on the cell surface, and since these are antigenic, the cell can become a target of the immune system of the host.

Answer 233

Facilitates Membrane Fusion - present on the lipid evelope of the virus Can be pH independent such as in HIV and Measles or pH dependent (Acidic) fusion proteins, such as HA in influenza virus- Low pH in endosome promotes fusion of envelope with endosomal membrane; lysis of nucleocapsid by lysosomal proteases, and release of viral genome The F (Fusion) protein catalyzes membrane fusion at the cell surface at neutral pH. The viral nucleocapsid is then released into the cytoplasm

Answer 234

(Non-enveloped Viruses) Some non-enveloped viruses inject their genome into the host cytoplasm through creation of a pore in the host membrane.

Answer 235

i.e. Feline Infectious Peritonitis (FIP)Virus - where a defective antibody attachs to the surface of the virus and it allows the virus to enter the host cell At same time, Antibodies against spike protein of FIP virus cannot clear the virus from host. Rather these antibodies bind to FIP virus spike proteins and facilitate entry of viruses into host cells through the antibody (IgG)-Fcγ receptor. These enhances the entry of viruses into host cell.

Answer 236

 Release of Viral Genome in Host Cell.  Virion can no longer be detected; known as the “eclipse period” Uncoating  Some animal viruses begin to uncoat after binding to the external receptor, but are not completely uncoated until inside the cell (Poliovirus).  Uncoating in some animal viruses requires a complex series of steps involving both host and viral gene products (Poxvirus).  In some other viruses, such as retroviruses and reoviruses, the first stages of the viral replication cycle (transcription, replication) actually occur inside the capsid.  Loss of infectivity of Virions.

Answer 237

viral genome serves as both erves both, as genomic & mRNA

Answer 238

 Viral mRNAs are translated by cellular protein synthetic apparatus.  The Viral mRNA must conform to the requirements of host cell translation system, i.e. the host cell can recognize the mRNA and translate same.  A series of modifications occur, known as Processing of Primary RNA Transcript/Pre- RNA  After processing, mRNAs are translated in the cytoplasm.  Viral mRNAs produced in the nucleus must also be exported to the cytoplasm. **To be reconized by the host ribosome, the virus must first have a cap and a tail**

Answer 239

1. Capping 2. Addition of 3’ poly-adenylated tails 3. Splicing

Answer 240

1. Capping: Addition of 7-methylguanosine to the 5 ́ end of RNA.  Stability of mRNA  Binding of mRNA to Ribosomes  Mark mRNA as “Self”  How Caps are Synthesized:  Can be Synthesized by host cell enzymes. –e.g. Retroviruses, Adenoviruses  Can be Synthesized by viral enzymes. –e.g. Poxviruses, Reoviruses  Cap snatching: virus steal caps from host Cap mRNAs. –e.g. Influenza

Answer 241

 PolyA tails interact with PolyA-binding protein: important for translation.  Viral mRNAs can be polyadenylated by host or viral enzymes 3'-Polyadenylation: **ESSENTIAL FOR TRANSLATION** A stretch of adenylate residues are added to the 3' end. The poly-A tail contains ~ 250 A residues in mammals. The major signal for the 3' cleavage is the sequence AAUAAA. Cleavage occurs at 10-35 nucleotides downstream from the specific signal sequence. A second signal is located about 50 nucleotides downstream from the cleavage site.

Answer 242

3. Splicing RNA splicing is a process that removes introns and joins exons in a primary transcript.

Answer 243

An exon is the portion of a gene that codes for amino acids

Answer 244

An intron is a portion of a gene that does not code for amino acids.

Answer 245

A. Constitutive Splicing: Every intron is spliced out; Every exon is spliced in. B. Alternative Splicing: All introns spliced out; Only selected exons spliced in. Result: mRNAs having different coding information derived from a single gene.

Answer 246

• Monocistronic mRNA that encodes one polypeptide • Polycistronic mRNA that encodes several polypeptides

Answer 247

open reading frame codes for the protein

Answer 248

1. can either translate into polyprotein and then proteases turn it into functional proteins 2. or an endonuclease turns into monocistronic mRNAs, which are then translated into functional proteins i. e. HIV: protease inhibitors

Answer 249

 Enzymes  Structural proteins  Viral Nonstructural Proteins  Regulatory proteins  Inhibitors

Answer 250

 Assembly of Virus Genome and Proteins into New Virions follow a Specific Order.  All components, including nucleic acids and proteins, are packaged to form mature Virions.  May take place in Nucleus Cytoplasm Plasma/Cell Membrane (Most Enveloped Viruses)

Answer 251

• Naked virions Lysis of host cell • Enveloped virions Budding

Answer 252

Bursting of cell popcorn coming out of a popcorn bag

Answer 253

Flaviviruses, Arteriviruses, Coronaviruses and Bunyaviruses mature by budding through the membranes of Golgi apparatus or Endoplasmic Reticulum (ER). Vesicles containing the virus then migrate to the plasma membrane and are released by exocytosis. Part on the right- exocytosis

Answer 254

1. Extracellular Spread Same Replication cycle repeated in new host cell and so on..... Released Viruses in Extracellular Milieu (environment). Travel to new cell.--- 2. Intercelluar spread 3. nuclear spread

Answer 255

Cell-to-Cell Spread of Viruses 2. Intercellular Spread: Spread from cell-to-cell without contact with extracellular milieu. Results in Rapid Virus Dissemination, **evasion of Immune system,** and Persistent Infections. Viruses can either utilize existing cell-cell contacts or exploit basic cell adhesion biology to deliberately establish contact between infected and uninfected target cells for the purpose of efficient spreading. Inter-Cellular Transmission of Viruses: Cell–cell plasma-membrane fusion followed by movement of infectious viral material (shown as viral cores) into the uninfected target cell. Herpesviruses, paramyxoviruses and retroviruses Passage of virions across a tight junction. Herpesviruses Movement of virions across a neural synapse. Rabies Virus Viral induction of actin- or tubulin-containing structures. Poxviruses Viral subversion of actin-containing structures, form Filopodial bridges. Retroviruses Membrane nanotube subversion. HIV-1 Virological synapses. Retroviruses **Seen in HIV, Herpesvirus, Measles, etc.**

Answer 256

The viral genome is integrated into the host cell genome and passed down to next progeny or generation of host cells, eg., Retrovirus

Answer 257

refers to the ability of a Virus to cause Disease in Host (i.e., harm the host).

Answer 258

The Virus which causes Disease is called a Pathogen

Answer 259

Pathogenesis is the manner/mechanism of development of a Disease.

Answer 260

The term Virulence is used as a quantitative or relative measure of the degree of pathogenicity of the infecting virus.

Answer 261

Not Virulent (Not harmful to the host).

Answer 262

Virulence is not an absolute property of a Virus, but depends on many variables Virus variables:  Virus strain (Genetic Makeup of the Virus/Strain Variation)  Portal of entry of Virus in Host  Tropism to Host Organs  Dose of Infection  Immuno evasion host variables:  Host Species  Host Immunity  Expression of Critical Receptors  Host Physiological factors (Nutrition status, Age, Hormonal Factors, Stage of Cell Differentiation)  Interferons, Other Inhibitors  Fever

Answer 263

The dose of the virus required to cause death in 50% of animals

Answer 264

The dose of virus that will infect 50% of an experimental group of hosts/animals.

Answer 265

Ratio of the dose of a particular strain of virus that causes infection in 50% of individuals [infectious dose 50 (ID50)] to the dose that kills 50% of individuals (LD50).

Answer 266

The lower the ID50 and LD50, the more viru- lent the organism

Answer 267

 Degree of Severity of illness (Clinical signs)  Incubation Period  Degree of Severity, location, and distribution of gross, histologic, and/or ultrastructural lesions in affected animals.

Answer 268

Virulence can be measured as the proportion of infections that are fatal (case: fatality rate) or by the survival time until death. In this example, various strains of myxoma virus, a poxvirus of rabbits, were compared after subcutaneous inoculation NC: not calculable.

Answer 269

Degree & Severity of Pathological lesions can be used to measure virulence.

Answer 270

1. Entry of Viruses & Primary Replication 2. Spread, Tropism, & Infection of Target Organs 3. Virus-Cell Interactions, Secondary replication 4. Tissue & Organ Injury 5. Shedding

Answer 271

**You have to have a breach in the skin.** Defenses  Dense outer layer of Keratin  Low pH  Presence of Fatty Acids  Bacterial flora  Dryness  Components of Innate and Adaptive Immunity (migratory dendritic cells: Langerhans cells)

Answer 272

1. Bite of Arthropods 2. Bite of Infected Animal 3. Contaminated Objects

Answer 273

Conjunctiva Oropharynx Genitourinary Tract Rectum Defenses  IgA (Antibodies)  Virucidal proteins

Answer 274

Defenses:  Mucous membrane of oral cavity & esophagus  Acidity of the stomach  Alkalinity of Intestine  Layer of mucus covering the gut.  Lipolytic activity of Bile.  Proteolytic activity of Pancreatic enzymes  Defensins (host defense peptides)  IgA  Scavenging Macrophages

Answer 275

Defenses:  Mucociliary blanket  Alveolar macrophages  NALT (nasal associated lymphoid tissue)  BALT (bronchus-associated lymphoid tissue)  Temperature Gradient

Answer 276

1. Replicate in epithelial cells at the site of entry 2. Local spread by infecting contiguous cells 3. Produce localized infections 4. Shedding 5. May or may not proceed to adjacent subepithelial tissues or beyond

Answer 277

 After replication at site of entry, viruses can remain localized or spread to other tissues.  After traversing the epithelium, Viruses may reach the subepithelial layers, which may be facilitated by: (1) inflammatory response to virus infection and/or destruction of epithelium, or (2) by transport pathways like **transcytosis.**  Viruses should overcome local host defense.  Directional shedding of viruses from the infected epithelium is critical to subepithelial spread. Apical release facilitates virus dispersal, whilst basolateral release provides access to underlying tissues, facilitating systemic spread.  In subepithelial tissues, viruses get access to lymphatics, phagocytes and tissue fluids. argeted migration and replication of virus within phagocytic leukocytes, specifically dendritic cells & macrophages, and, or lymphocytes.  Some viruses may pass straight through lymph nodes to enter blood stream.  Some viruses are processed and epitopes presented to Helper T-Cells: Immune response.

Answer 278

Infection spreads beyond the primary site of infection.

Answer 279

If a number of organs or tissues are infected.

Answer 280

Viremia: The presence of a virus in the blood. Virus may be free in blood or in a cell, such as lymphocytes.

Answer 281

Primary Viremia: Initial entry of virus into the blood after infection Secondary Viremia: Virus has replicated in major organs & once more entered the circulation

Answer 282

Passive Viremia: Direct inoculation of virus in host, such as contaminated syringe or bite of arthropods. No initial replication elsewhere in host before.

Answer 283

Active Viremia : Viremia following initial virus replication in host. Release of virions from the initial site of replication, such as lymphatics or epithelium of intestine, to the blood stream.

Answer 284

1. Free in Plasma (Parvovirus) Short duration Viremia 2. Cell-Associated Viruses Tend to cause Prolonged Viremia. Multiply in Macrophages or Lymphocytes.

Answer 285

Varies * Macrophages may fail to phagocytose host cells containing virions. Prolonged Viremia * Virions may be phagocytosed & transferred passively to adjacent cells, where replication begins * Tissue invasion via carriage of virus inside monocytes/macrophages that emigrate through the walls of small blood vessels (Trojan Horse) * Virions may be phagocytosed and destroyed * Virions may be phagocytosed by macrophages & then may replicate in them *

Answer 286

(Trafficking Monocytes Transport Viruses) Wooden horse= macrophage city= tissue cell virus enters wooden horse and then the macrophage then goes to the tissue and the viruses come out of the wooden horse

Answer 287

• Mononuclear phagocytes in the spleen, liver, bone marrow * Antibody clearance * Complement-mediated clearance

Answer 288

Examples:  Herpes simplex virus exhibits low neuroinvasiveness of the central nervous system, but high neurovirulence. It always enters the peripheral nervous system, but rarely enters the central nervous system. When it does, the consequences are almost always severe, if not fatal.  Mumps virus exhibits neuroinvasiveness, but low neurovirulence. Most infections lead to invasion of the central nervous system, but neurological disease is mild.  Rabies virus exhibits high neuroinvasiveness and high neurovirulence. It readily infects the peripheral nervous system and spreads to the central nervous system with 100% lethality unless antiviral therapy is administered shortly after infection.

Answer 289

Neurotropic virus: Viruses that can infect neural cells. D. Spread via Nerves Infection may occur by neural or hematogenous spread.

Answer 290

Neuroinvasive virus: Viruses that enter the central nervous system (spinal cord and brain) after infection of a peripheral site.

Answer 291

Neurovirulent virus: Viruses that cause disease of nervous tissue, manifested by neurological symptoms and often death.

Answer 292

* Transport of virus within axons * Transport of virus in perineural lymphatics * Transport of virus in the endoneu- ral space * Transport of viruses via infected Schwann cells Centripetal movement of virus: Towards the CNS/Brain Centrifugal movement: From CNS, within peripheral nerves, to other locations in body.

Answer 293

Retrograde Spread: Travel opposite direction of nerve impulse flow. Invades axon terminals and then spread to Dendrite or cell body, and then cross synapse to reach next axon terminal.

Answer 294

Anterograde Spread: Travel in direction of nerve impulse flow. Virus invades dendrites or cell bodies and then spread to axon terminals, and then cross synaptic contacts to invade dendrite of next neuron.

Answer 295

can enter from the blood or from the nose

Answer 296

Towards the CNS/Brain

Answer 297

From CNS, within peripheral nerves, to other locations in body. **RABIES**

Answer 298

Methods: Increasing permeability of endothelial cells through the secretion of TNF (Tumor Necrosis factor). Breakdown of endothelial cell junctions through Matrix- metalloproteinase (MMP). Trojan horse (Trafficked by Monocytes)

Answer 299

Local Systemic ## Footnote Site of pathology portal of entry distant sites Incubation short long period (IP) Viremia NO YES Duration variable lifelong of immunity Secretory IgA very important not important

Answer 300

 Shedding of infectious virions is crucial to the maintenance of infection in populations.  Critical to virus transmission: The amount of virus shed in an excretion or secretion is important in relation to disease transmission.  Some viruses are shed from a variety of sites and several sites.  Acute infection: usually intensive shedding over short time period.  Persistent infections: can be shed at lower titers for months to years. can be shed in as many ways as you can get it!

Answer 301

The specificity/Affinity of a virus for a particular host tissue An enteric virus replicates in gut, but not in lungs. A respiratory virus replicates in lungs, but not in nerves.

Answer 302

Can Replicate in more than one host Organ/Tissue

Answer 303

 Receptors on Host Cell  Viral attachment proteins  Viral enhancers: Gene activators that increase the efficiency of transcription of viral or cellular genes, facilitating Virus Replication.  Cellular protease requirement  Temperature of replication  Acid lability and protease digestion  Transcriptional control of tropism  Anatomic barriers  Host organ response to infection

Answer 304

* A general term applied to any temporary eruption on the skin * A rash usually is a shade of red Varies with the disease in question

Answer 305

Rash of Lyme Disease

Answer 306

Can be localized (Papilloma) or disseminated (lumpy skin disease). Vesicles- rupture with ulcers- FMD in Pig, Vesicles on coronary band Ulcers in FMD Nodules in Lumpy Skin Disease, Cattle Warts caused by Papillomavirus Warts are benign (not cancerous) skin growths that appear when a virus infects the top layer of the skin. Papules(solid, crusty elevated), Papular stomatitis in cattle Erythema in Hog cholera Erythema, Reddening of skin, consequence of systemic viral infections (endothelial injury in blood vessels throughout body, including those of the subcutaneous tissues)

Answer 307

Rotavirus, Norovirus are INGESTED Parvovirus, Pestivirus Hematogenous spread, systemic infection 1. Destruction of enterocytes due to Viral replication, Hypersecretion 2. Gastrointestinal disease, Malabsorption, Diarrhea 1. Pronounced de4qhydration, Acidosis, Hemoconcentration

Answer 308

Tropism for different parts of the respiratory tract with considerable overlap.  Loss of ciliary activity  Loss of integrity of the lining mucus layer  Multifocal destruction of epithelium  Inflammation **Example: Avian Infectious Bronchitis**  Exudation  Influx of inflammatory cells  Obstruction of air passages  Hypoxia & Respiratory distress  Secondary Bacterial Infection

Answer 309

Infection of the Respiratory Tract

Answer 310

Lytic infections of neurons by togaviruses, flaviviruses, herpesviruses, or other viruses leads to encephalitis or encephalomyelitis characterized by neuronal necrosis, phagocytosis of neurons (neuronophagia), and perivascular infiltrations of inflammatory cells (perivascular cuffing). **Examples:** Neuronal vacuolation in Prion disease Progressive Demyelination- Canine Distemper

Answer 311

Petechial and ecchymotic hemor- rhages Disseminated intravascular coagu- lation [DIC] Edema Infarction Ischemic necrosis

Answer 312

Damage to Endothelium Hemorrhages Petechiae hemorrhage (Pin-Point/Small spots ) ``` Ecchymoses hemorrhage( on bottom right) (larger areas of hemorrhage, ill-defined margins) ```

Answer 313

 Complication arising from Viral Infection of Blood Vessels.  Widespread activation of the clotting cascade that results in the formation of blood clots in the small blood vessels throughout the body.  Some of these clots can clog the vessels and cut off blood supply to organs such as the liver, brain, or kidneys.  Lack of blood flow can damage the organ and it may stop working properly, often resulting in Ischemia and Necrosis.  Over time, the clotting proteins in your blood are consumed or "used up." When this happens, severe bleeding can occur from various sites.

Answer 314

• This is the abnormal development or arrests in development of the embryo or fetus May result in death or malformations during the antenatal period • Susceptibility to teratogens Varies with the species and stage of develop- ment, decreasing with fetal age i.e. cerebellar hypoplasia, Arthrogryposis

Answer 315

Congenital hydranencephaly, calf showing recumbence, depression, and a slightly dome-shaped skull (BVDV infection)

Answer 316

Porencephaly (Bovine Viral Diarrhea Virus, BVDV)

Answer 317

Non-pregnant animal Usually Mild infection, Scours, Milk drop, reduced WBCs

Answer 318

 Defined as Tissue injury mediated by host immune response to Virus infection. It is the price paid by the host to clear a viral infection.  Depends on the delicate balance between the protective and destructive effects of the host immune response to viruses.  Immunopathology is often the cause of damage with viruses that are relatively non- cytolytic and persistent, i.e. infected cells are not immediately destroyed and immune response becomes chronic.  If the immune response clears the infection by destroying a small number of virus- infected cells, the host survives with minimal symptoms and no permanent damage.  On the other hand, if a large number of cells are infected before immune induction, the same immune mediated destruction can cause severe or fatal pathological consequences.

Answer 319

Tissue damage mediated by hypersen- sitivity reactions Autoimmune diseases, eg, moon blind- ness in a horse Inflammation-mediated tissue damage, eg, fibrosis Immunodeficiency disorders

Answer 320

T cells, for example, can directly destroy virus-infected cells or release cytokines, such as tumor necrosis factor (TNF), that damage cells.  There may be Cytotoxic cell mediated lysis/killing of infected host cells.  With some non-cytopathic virus infections, such as HCV and HBV, destruction of infected cells by CD8+ effector T cells is the main cause of damage to the liver.  There may be release of cytokines from T cells (CD4+ and CD8+) and other cells that cause inflammation and tissue damage that becomes chronic against persistent virus infections.  CD4+ cells elaborate far more cytokines than CD8+ cells and also activate other non-specific effector cells, such as neutrophils.

Answer 321

Cytokines are a broad and loose category of small proteins that are important in cell signaling. They act as mediators and regulators of immune processes, but also cause inflammation. These include:  Monokines, cytokines produced by mononuclear phagocytic cells  Lymphokines, cytokines produced by activated lymphocytes, especially Th cells  Interleukins, cytokines that act as mediators between leukocytes

Answer 322

 Invading viruses and their replicative intermediates can be recognized by several innate immune receptors expressed either at the host cell surface or within cells, such as Toll-like receptors (TLRs).  Persistent activation of these receptors of innate host cells by viruses causes production of pro-inflammatory cytokines and interferons, as well as signals that recruit and activate cells involved in inflammation.  Injury can also be mediated by free radicals, such as Nitric oxide and Superoxide. Normally, they inhibit viral replication. But when produced in abundance, cause cell damage.

Answer 323

 Antibody responses to viruses may also contribute to tissue damage.  This occurs when antibody binds to an infected cell, activates complement and causes an inflammatory reaction.  Alternatively, antibody mediated inflammatory reactions involve toxicity following:  Engagement of IgG with Fc receptors on inflammatory cells, which causes inflammatory mediator release.  Following deposition of viral antigen–antibody complexes in capillary beds, leading to activation of the complement cascade.

Answer 324

Spike proteins on Feline Infectious Peritonitis Virus (FIPV) bind to antibodies. These antibodies fail to neutralize the virus. Instead there is antigen-antibody immunocomplex formation which activates the complement cascade and the result is vasculitis (inflammation in the blood vessels) and edema.

Answer 325

Feline Infectious Peritonitis (Immune Complex-Mediated Vasculitis) Distended abdomen

Answer 326

Infection and damage to mononuclear phagocytes can protect an invading virus from phagocytic removal. Moreover, these infected cells may exhibit aberrant behavior, resulting in a cascade of events that are detrimental to the host.

Answer 327

Infectious Bursal disease: Virus replication causes atrophy of the bursa and a severe deficiency of B lymphocytes, resulting in immuno- suppression. As a result, infected birds become susceptible to other pathogens.

Answer 328

* Clinical signs and symptoms are not evident • Too few cells may be infected * Stimulate host immune response * Possible source of virus spread

Answer 329

(Short-term Infection)  Short clinical course.  Rapid clearance from host immune response.

Answer 330

Persistent infections, per se, in which infectious virus is demonstrable continuously, whether or not there is ongoing disease. Disease may develop late, often with an immunopathologic or neoplastic basis, or in other instances, there may be no manifestation of clinical signs. The pathogen is not cleared efficiently by the adaptive immune response Persistent Infections are Important:  Recrudescent episodes of disease in the individual host.  Immunopathology  Survival of virus in host and continuous shedding, source of spread of Virus.

Answer 331

Latent infections, in which infectious virus is not demonstrable except when reactivation occurs. Reactivation is often stimulated by immunosuppression and/or by the action of a cytokine or hormone.  Viral latency may be maintained by:  Restricted expression of genes that prevents the expression of proteins which, otherwise, would have killed the infected cells.  Virus genome maintained indefinitely in cell by integration of viral nucleic acid into host cell DNA, or by carriage of viral nucleic acid in episomal form. **Example: Infectious Bovine Rhinotracheitis**

Answer 332

Acute infection followed by chronic infection in which the virus is continuously shed from or is present in infected tissue.  Established if host immunity is unable to clear virus from acute infection.  Not all chronic infection may start as acute infection. Example: Foot and Mouth Disease in Cattle

Answer 333

 Prolonged incubation period, lasting months or years.  Quantities of infectious virus gradually increase during a very long preclinical phase  Slow progressive lethal disease. Example: Prions

Answer 334

Cell Death  Lysis  Apoptosis

Answer 335

Persistent Infection

Answer 336

Tumor cells

Answer 337

Cytopathic effect or cytopathogenic effect (abbreviated CPE) refers to damage or morphological changes to host cells during virus invasion.  Primary effect induced by viral replication and viral proteins toxic to host cells.  Secondary effects of metabolic needs of the virus. 1. Complete destruction of cells- Most severe form of CPE. All cells in the monolayer rapidly shrink, become dense (pyknosis), and detach from the glass within 72 hours Eg. Enteroviruses 2. Subtotal destruction of Cells- Consists of detachment (death) of some, but not all of the cells in the monolayer.Eg. Togaviruses, some picornaviruses and some paramyxoviruses 3. Focal destruction of cells- Produce localized areas (foci) of infection. Eg. Herpesviruses and poxviruses.

Answer 338

a degenerative condition of a cell nucleus marked by clumping of the chromosomes, hyperchromatism, and shrinking of the nucleus

Answer 339

 Cell lysis  Cell rounding  Cell detachment  Vacuoles in cytoplasm  Inclusion bodies  Syncytium formation  Antigenic changes in cell membrane  Swelling and Clumping

Answer 340

 Involves the fusion of the plasma membranes of four or more cells to produce an enlarged cell with four or more nuclei. Prone to premature Cell Death.  Result from the fusion of an infected cell with neighboring infected or uninfected cells.  Enveloped viruses specifically direct the insertion of their surface glycoproteins, including fusion proteins, into host‐cell membranes as part of their budding process, often leading to membrane fusion and syncytium formation.  Syncytia formation may be the only detectable CPE of some paramyxoviruses.

Answer 341

 An abnormal structure in a cell nucleus or cytoplasm or both, such as aggregates of proteins, having characteristic staining properties and associated with certain viral infections.  Help to identify certain viral infection. Inclusion bodies can be:  Accumulation of viral components, such as Negri bodies consist of ribonuclear proteins produced by the rabies virus.  Result from degenerative changes in cell, such as Owl’s eye inclusion bodies seen in herpesvirus infection  Crystalline aggregates of virions, such as in adenovirus infection.

Answer 342

recognizes/Affinity for acid dyes, such as eosin. Appear Pinkish upon staining.

Answer 343

recognizes/affinity for basic dyes, such as hematoxylin. Appear Purplish Blue upon staining.

Answer 344

Large DNA viruses, such as poxvirus, produce enzymes that may degrade cellular DNA.

Answer 345

 Indirect consequence of viral effects on host‐cell protein synthesis that decrease the availability of transcription factors required for RNA polymerase activity.  Certain viruses encode specific transcription factors to regulate the expression of their own genes, and these factors sometimes modulate the expression of cellular genes as well, such as herpesviruses.  Some viruses, such as influenza and herpesvirus, encode proteins that inhibit polyadenylation and splicing of host cell primary mRNA transcripts required to form mature mRNA.

Answer 346

 Inhibition of Host‐Cell Protein Synthesis :  Production of viral enzymes that degrade cellular mRNAs  Production of factors that bind to ribosomes and inhibit cellular mRNA translation  Alteration of the intracellular ionic environment favoring the translation of viral mRNAs over cellular mRNAs  Production of large excess of viral mRNA that outcompetes cellular mRNA for host ribosomes  Some viruses cause lysosomes to release their hydrolytic enzymes, which then destroy the host cell

Answer 347

proton on the outside of a virus that helps it fuse to the cell membrane

Answer 348

 Interference with Cellular Membrane Function:  Promotion of Cell Fusion (Syncytium Formation)  Affect ion exchange and membrane potential  Induce the synthesis of new intracellular membranes or the rearrangement of previously existing ones  Damage to the cytoskeleton resulting in changes in cell shapes. The cytoskeleton is responsible for the structural integrity of the cell, for the transport of organelles through the cell, and for certain cell motility activities.

Answer 349

Apoptosis is the process of programmed cell death, which is essentially a mechanism of cell suicide that the host activates as a last resort to eliminate viral factories before progeny virus production is complete.  Different from Lysis where viral replication is complete, host cell is destroyed and new virions released.

Answer 350

Activation of host‐cell caspase enzymes mediate death of the cell. Once activated, caspases are responsible for degradation of the cell’s own DNA and proteins.

Answer 351

The mitochondrial pathway is activated as a result of increased permeability of mitochondrial membranes subsequent to cell injury, such as that associated with a viral infection. apoptotic pathway

Answer 352

The Extrinsic (Death Receptor) Pathway: The extrinsic pathway is activated by engagement of specific cell‐membrane receptors, which are members of the TNF receptor family (TNF, Fas, and others). Thus binding of the cytokine TNF to its cellular receptor can trigger apoptosis. Similarly, cytotoxic T lymphocytes that recognize virus‐infected cells in an antigen‐specific manner can bind the Fas receptor, activate the death domain, and trigger the executioner caspase pathway that then eliminates the cell before it becomes a functional virus factory.

Answer 353

Apoptotic Pathways Cytotoxic T lymphocytes and natural killer cells can also initiate apoptosis of virus‐ infected target cell, utilizing preformed mediators such as perforin and granzyme that directly activate caspases in the target cell.

Answer 354

 Non‐cytocidal viruses usually do not cause immediate death of cells in which they replicate.  They often cause persistent infection during which infected cells produce and release virions, but overall cellular metabolism is little affected.  In many instances, infected cells even continue to grow and divide.  Can produce important pathophysiologic changes in their hosts by affecting crucial functions that are associated neither with the integrity of cells nor their basic housekeeping functions.  Damage to the specialized functions of differentiated cells may still affect complex regulatory, homeostatic, and metabolic functions, including those of the central nervous system, endocrine glands, and immune system.  With few exceptions (e.g., some retroviruses), these slow progressive changes ultimately may lead to cell death.  However, in the host animal, cell replacement occurs so rapidly in most organs and tissues that the slow fallout of cells as a result of persistent infection may have no effect on overall function.  But, terminally differentiated cells such as neurons (Nerve Cells), once destroyed, are not replaced, and persistently infected differentiated cells may lose their capacity to carry out specialized functions.  This type of interaction can occur in cells infected with several kinds of RNA viruses, notably pestiviruses, arenaviruses, retroviruses, and some paramyxoviruses.

Answer 355

Cell transformation is the changing of a normal cell into a cancer cell.

Answer 356

Neoplasia is a descriptive term that denotes an abnormal tissue overgrowth that may be either localized or disseminated. It is the process that leads to the formation of neoplasms (syn. carcinogenesis).

Answer 357

Oncology is the study of neoplasia and neoplasms

Answer 358

A benign neoplasm is a growth produced by abnormal cell proliferation that remains localized and does not invade adjacent tissue

Answer 359

A malignant neoplasm (syn. cancer) is locally invasive and may also be spread to other parts of the body (metastasis)

Answer 360

Oncogenic Viruses: Viruses that cause or give rise to tumors.

Answer 361

Neoplasms (tumors) arise as a consequence of the dysregulated growth of cells derived from a single, genetically altered progenitor cell.

Answer 362

Metastasis is the spread of cancer cells from the part of the body where it started (the primary site) to other parts of the body. When cancer cells break away from a tumor, they can travel to other areas of the body through the bloodstream or the lymph system, and develop secondary tumors in other parts of body.

Answer 363

Encode proteins that function in normal cellular growth and differentiation  Encode growth factor proteins  Encode growth factor receptors  Encode transcription factors  Encode intracellular signaling proteins  Encode Signal Transducers Proto-Oncogenes  Proto‐oncogenes are often involved in growth signaling and anti‐apoptotic pathways. Encode growth factor proteins  Encode growth factor receptors  Encode transcription factors  Encode intracellular signaling proteins  Encode Signal Transducers Normally mitosis (cell division) is a carefully regulated event, requiring the activation of one protein to activate another, in what is known as a signal transduction cascade.

Answer 364

Plays a role in keeping cell division in check. Encodes proteins that regulates and inhibits uncontrolled growth

Answer 365

 Mutated forms of proto-oncogenes or aberrantly expressed proto-oncogenes.  Encode proteins that somewhat resemble products of proto-oncogenes, but differ WHY?  These onco-proteins function in an unregulated manner, i.e. do not respond to regulatory signals.  Synthesis of aberrant growth factors, growth factor receptors, etc. that trigger uncontrolled proliferation of cells.  Defective differentiation of cells.  Failure to undergo apoptosis. **Under normal circumstances membrane-bound receptors require the binding of their ligand to be in an activated state. In contrast, receptors encoded by oncogenes do not require the regulatory step of ligand binding to be active.**

Answer 366

Encode proteins that inhibit cell proliferation (by holding cell cycle at G1 phase). Functions:  Inhibits the expression of genes that are essential for the continuing of the cell cycle.  Connecting the cell cycle to DNA damage, i.e. if cell has damaged DNA it will not divide.  Repair of damaged DNA  If repair effort fails, apoptosis of cells  Adhesion proteins known as metastasis suppressors that prevent spread of cancer cells, or metastasis.

Answer 367

 One of the first tumor‐suppressor genes to be discovered was the Rb gene.  The Rb protein alternates between a phosphorylated state and Un‐phosphorylated state. Rb is phosphorylated by enzyme Cyclin Dependent Kinases (CDKs).  The E2F transcription factor is necessary for the expression of a number of cell‐cycle‐ specific genes.  **The role of Un‐phosphorylated Rb is to bind to the transcription factor E2F, preventing its activity, and not allowing cell division to proceed from G1 to S phase.** ** On the other hand, Phosphorylated Rb cannot bind E2F, this releases E2F from its inhibition and allows the cell cycle to progress.**  A loss of normal Rb function leads to the loss of control over the cell cycle  Another tumor suppressor protein P16 blocks CDK. So CDK cannot phosphorylate Rb. Rb is free to bind and inhibit action of E2F

Answer 368

P53 activates the DNA repair system and stops the cell cycle at the G1 checkpoint (before DNA replication). if not then apopotisis

Answer 369

 Viruses that cause cancer.  Oncogenic viruses generally have a DNA genome, or generate a DNA provirus after infection (Retrovirus)  Cells transformed by oncogenic viruses usually have viral DNA integrated into host genome. These integrated DNA may be a part or all of the viral genome.  However, the genome of few viruses may remain episomal, replicating in each step with host cell chromosome, i.e. the genome never integrates into host genome, but has an autonomous replicating system. Found in B cells infected with Epstein-Barr virus and in cells infected with Papillomavirus.

Answer 370

 Although retroviruses are the most important oncogenic viruses in animals, certain DNA viruses are also significant, including papillomaviruses, polyomaviruses, herpesviruses  DNA oncogenes are an essential part of the viral genome, encoding proteins which alter patterns of gene expression and regulation of cell growth (induce transformation).  In every case the relevant genes encode early proteins having a dual role in virus replication and cell transformation.  Oncogenes of DNA viruses have no homologue or direct ancestors (c-onc genes/ protooncogenes) among cellular genes of the host. DNA tumor viruses interact with cells in one of two ways: (1) productive infection in Permissive cell, in which the virus completes its replication cycle, resulting in cell lysis, or (2) non-productive infection in Nonpermissive cell, in which the virus transforms the cell without completing its replication cycle. During such non-productive infection, the viral genome or a truncated version of it is integrated into the cellular DNA; alternatively, the complete genome persists as an autonomously replicating plasmid (episome).

Answer 371

 Papillomaviruses produce papillomas (warts) on the skin and mucous membranes of most animal species.  These benign neoplasms are hyperplastic epithelial outgrowths that generally regress spontaneously.  Occasionally, however, they may progress to malignancy, which in part is a property of specific virus strains. **Example, cervical carcinoma in women.**  In benign warts, the papillomavirus DNA is episomal, meaning it is not integrated into the host-cell DNA and persists as an autonomously replicating episome.  In papillomavirus-induced malignant cancers the viral DNA is integrated into that of the host. Thus, integration probably is necessary for malignant transformation.  Integration disrupts one of the early genes, E2, which is a viral repressor.  However, the viral oncogenes (e.g., E6 and E7) remain intact and cause the malignant transformation. **block p53**

Answer 372

All RNA tumor viruses belong to the family Retroviridae.

Answer 373

Inserted proto-oncogene becomes oncogene/v-onc gene in virus. \>Mutation \>Loss of introns/cell elements that control the expression of this gene C-onc/proto-oncogene is inserted in virus genome by recombination between proviral DNA and Host DNA  Acute transforming retroviruses are directly oncogenic by carrying an additional viral oncogene, v-onc.  The retroviral v-onc originates from a host c-onc gene/proto-oncogene which is inserted into the virus genome usually by recombination events between provirus DNA and host DNA, i.e. v-onc genes are c-onc genes separated from host genome and inserted in virus genome.  Remember: c-onc genes/proto-oncogenes are host genes that encode important cell signaling products that regulate normal cell proliferation.  v-onc genes are separated from the cellular machinery that normally controls gene expression (lacks introns), so they have power of unregulated expression.  Moreover, the c-onc/proto-oncogene (inserted in virus genome) also mutates accentuating its transformation activity.  v-onc genes are under the control of the **viral LTRs(long term repeats) ,** which are strong promoter- **Allows the gene to express more and more, which makes the condition worse**

Answer 374

Gene recombination

Answer 375

after the proto oncogenes has been put into the host's DNA and it starts mutating under no regulatory contro

Answer 376

Virus gene do not contain v-onc gene. The integration of retroviral genes into host chromosomal DNA can occur at promoter or enhancer sites that drive the increase in proto- oncogene/c-onc gene expression, leading to malignant transformation of the cell.

Answer 377

DNA sequence at which DNA-dep RNA poly- merase binds to initiate transcription

Answer 378

A transcriptional regulatory sequence located some distance from the promoter; it increases the rate of initiation of transcription

Answer 379

1. Cells are more spindle-shaped 2. Loss of Contact Inhibition

Answer 380

 New antigens appear on the surface of tumor cells that may provoke an immune response.  These are abnormal proteins that arise from mutations and are broadly classified into.  Products of Mutated Oncogenes and Tumor Suppressor Genes (Tumor-Specific antigens)  Products of Other Mutated Genes (Tumor-associated antigens)  Tumor antigens are usually classified into 5 types ( in picture)  The immune system recognizes these abnormal antigens as foreign and tries to destroy the tumor cells.  However, these abnormal molecules often are not appropriately presented to cells of immune system, such as cytotoxic T cells.

Answer 381

Feline oncornavirus membrane- associated antigen

Answer 382

 Innate immune defenses exhibit neither antigen specificity nor memory.  They provide a critical line of first defense against viral infections because :  They are constantly present  They are operational immediately after viral infection  Are the only immune defense available for the first few days after viral infection A. Primary Physical and Chemical Defenses: Viruses must first breach the barriers at their portal of entry before they can cause infection in their respective hosts. These barriers often form the first line of defense.

Answer 383

1. The Skin 2. Mucous membrane 3. Gastrointestinal Tract 4. Respiratory Tract

Answer 384

(host defense peptides) with antiviral activity. Modulate the host immune response.

Answer 385

The respiratory tract from the nasal passages to the distal airways in the lungs is protected by the “mucociliary blanket,” which consists of a layer of mucus produced by goblet cells that is kept in continuous flow by the coordinated beating of cilia on the luminal surface of the epithelial cells that line the nasal mucosa and airways. Larger particles (larger than in diameter) are trapped on the mucociliary blanket and then swallowed or coughed out.

Answer 386

There is a temperature gradient between the nasal passages (33°C) and the alveoli (37°C) that plays an important role in the localization of infection. Thus, rhinoviruses, which infect the nasopharynx and cause the common cold, replicate well at 33°C but grow poorly at 37°C, while influenza virus, which infects the lower respiratory tract, shows the inverse temperature preference.

Answer 387

 NK cells are large lymphocytes that are defined by their cytoplasmic granules.  They provide early and non-specific resistance against viral infections.  The cytoplasmic granules of NK cells contain:  Perforin which can produce pores in plasma membranes  Granzymes – proteins that can initiate apoptosis. When NK cells release their cytoplasmic granules, they can kill adjacent cells. Natural killer cells are not antigen specific; rather, their activation requires differential engagement of cell-surface receptors in combination with stimulation by proinflammatory cytokines  NK cells mediate death of virus infected cells via apoptosis, and therefore, can eliminate infected cells before they release progeny virions.  Natural killer cells synthesize and release a variety of cytokines, including type II IFN and several interleukins that stimulate their own proliferation and cytolytic activity.

Answer 388

A. Healthy cells express self class I MHC molecules, which are recognized by inhibitory receptors, thus ensuring that NK cells do not attack normal cells. Note that healthy cells may express ligands for activating receptors (not shown) or may not express such ligands (as shown), but they do not activate NK cells because they engage the inhibitory receptors. B. In virus-infected cells, class I MHC expression is reduced so that the inhibitory receptors are not engaged, and ligands for activating receptors are expressed. The result is that NK cells are activated and the infected cells are killed.

Answer 389

 Cells at portals of virus entry possess surface receptors (pattern recognition receptors (PRR)) that recognize specific pathogen-associated molecular patterns (PAMPs), which are macromolecules present in viruses and other microbes, but not on host cells.  One class of PRRs are the toll-like receptors (TLRs)  These pattern recognition receptors (PPR) are expressed on and in a variety of different cells, including macrophages, dendritic cells, neutrophils, natural killer cells, endothelial cells, and mucosal epithelial cells.

Answer 390

 expression of IFNs and inflammatory cytokines such as tissue necrosis factor and interleukins-1 and -12 (IL-1, IL-12).  activation of phagocytic cells and endothelial cells with increased production of inflammatory mediators and cell-surface expression of adhesion molecules  Macrophages may initiate chemotaxis, bringing neutrophils to a site of inflammation.  However, persistent activation of these receptors by viruses can cause continuous production of inflammatory mediators (pro-inflammatory cytokines and interferons) and chemotaxis, resulting in immunopathology (damaging effects to host).

Answer 391

Toll-like Receptors

Answer 392

 Interferons (IFN) are a group of cytokines (complex glycoproteins) that are secreted by somatic cells in response to viral infections and to other stimuli.  They possess potent antiviral, immunomodulating and anti cancer properties. ** Interferons show no virus specificity.**  RNA viruses are stronger inducers of interferon than DNA viruses.  Being **glycoproteins,** interferons are orally inactive, and should be administered to the patient by parenteral route (Injection).

Answer 393

 **Type-I:** There are many type I interferons.  IFN- :  Leukocyte interferon  Produced in large quantities by plasmacytoid dendritic cells  Produced in smaller amounts by macrophages, monocytes, and lymphocytes).  Not host specific  IFN- :  Fibroblast interferon. Secreted by virus-infected fibroblast.  Generally Host species-specific. T**he two major type-I interferons (IFN- and IFN-) are produced by virus-infected cells within a few hours of viral invasion. The IFN binds to specific receptors of IFN-responding host cells, triggering the intracellular synthesis of antiviral proteins.**

Answer 394

 Inhibit Virus replication in Host Cells  Activate Natural Killer (NK) Cells to kill infected cells.  Increase expression of MHC-I molecules and antigen presentation.  Type-I IFNS also stimulate differentiation of monocytes into dendritic cells.  Maturation of dendritic cells.  Stimulates memory T cell proliferation.

Answer 395

 Activate a latent ribonuclease called RNAse L. RNAase L degrades viral RNA.  Induces synthesis of Mx proteins that bind and trap viral nucleocapsid and inhibit virus assembly.  Induce synthesis of Protein Kinase R (PKR) which prevents initiation of translation of viral RNA.

Answer 396

Induce synthesis of Protein Kinase R (PKR) which prevents initiation of translation of viral RNA. How type-I IFNs inhibit virus replication:

Answer 397

Autocrine: The infected cell secretes the IFN that acts on same cell, triggering apoptosis. Paracrine: The infected cell secretes IFN which acts on adjacent cells.

Answer 398

Type-II: Only one type of interferon, IFN-gamma( looks like y). Mostly Immunoregulatory.  Produced by antigen-stimulated T cells and Natural Killer (NK) cells  Labile at pH 2  Demonstrates host specificity

Answer 399

Type-III: At least three type 3 interferons have been identified, IFN-1, IFN-2 and IFN- 3.  Recently discovered.  Expressed in response to viral infections and activation of Toll-like-Receptors.  Primarily functions as immunoregulator.

Answer 400

 Cells utilize small, interfering, RNA molecules (RNAi) to silence genes as a means of regulating normal developmental and physiological processes, and potentially to interfere with virus replication.  Production of RNAi initiates formation of the RNA-silencing complex that includes an endonuclease that degrades those mRNAs with a sequence that is complementary to that of the RNAi.  Cells can utilize this mechanism to disrupt virus replication through the production of RNAi that are complementary to specific viral genes. **siRNA**

Answer 401

 Adaptive immunity includes humoral and cellular components.  Humoral immunity is mediated principally by antibodies released from B lymphocytes  Cellular immunity is mediated by T lymphocytes  Adaptive immunity is antigen specific, so that these responses take time (several days at least) to develop, and this type of immunity is mediated by lymphocytes that possess surface receptors that are specific to each pathogen  Adaptive immunity stimulates long-term memory after infection  Internal viral antigens usually elicit protective Cell Mediated Immune (CMI) response  Surface antigens elicit protective humoral and CMI responses  Viral infections usually do not provoke granulocytosis. Leukocytosis observed is commonly due to lymphocytosis and other mononuclear cells.

Answer 402

presence in peripheral blood of an increased number of granulocytes, i.e. Neutrophils, eosinophils, basophils, mast cells. viral infections do not provoke this

Answer 403

 Virus capsid and envelope proteins are antigenic.  Antibodies may be directed against viral proteins on free virions (capsid or envelope), or against viral proteins expressed on surface of infected cells.

Answer 404

Neutralizing antibodies prevent virus attachment and entry into host cells. They bind to the viral capsid or host envelope.

Answer 405

Coating of virions with antibodies. Antibody coated virion is recognized and phagocytosed by macrophages, and sometimes by neutrophils.

Answer 406

Clumping of Viruses (Immunocomplex formation) : Reduces the number of viral particles available for cell invasion

Answer 407

 Opsonization - enhancing phagocytosis of antigens  Chemotaxis - attracting macrophages and neutrophils  Lysis - rupturing membranes of foreign cells/Pathogens  Agglutination- clustering and binding of pathogens together (sticking)

Answer 408

Antibodies bind to viral antigens expressed on surface of host cells. These host cells are destroyed by phagocytosis (macrophages and NK cells), or by complement mediated cytolysis

Answer 409

Portions of immunogenic viral proteins produced in the cytosol of the infected cell are transported to the endoplasmic reticulum, where they associate with class I MHC molecules. This complex is directed to the cell surface, where the viral peptides can be recognized by antigen-specific cytotoxic T lymphocytes.  Cytotoxic T-lymphocytes (CTLs) are then able to recognize peptide/MHC-I complexes by means of their T-cell receptors (TCRs) and CD8 molecules and kill the cells to which they bind.  Binding of the CTL to the infected cell triggers the CTL to release pore-forming proteins called perforins, proteolytic enzymes called granzymes, and chemokines. Granzymes pass through the pores and activate the caspase enzymes that lead to apoptosis of the infected cell.

Answer 410

Antigenic Plasticity: Rapid changes in the structure of the viral antigen. May be the result of mutation, reassortment or recombination.  Due to change in antigen structure, the virus may become resistant to immunity generated by previous infection.

Answer 411

Antigenic Multiplicity: Antigenic variants with little or no cross-reactivity.  Example, there are more than 100 serotypes of rhinoviruses which are antigenically different from each other. So immunity against one serotype may not work against the other variants.

Answer 412

Negative Cytokine Regulation:  Blocking interferon receptor signal.  Virokines: Some viruses synthesize proteins which are homologs of cytokines/interferons. Epstein-Barr virus synthesizes vIL-10, a homolog of IL-10, and suppresses cytokine production by TH1 CD4+ cells.  Viroceptors: Some viruses encode proteins that are homologous to the receptors for cytokines. The secreted cytokine receptor homologs bind to cytokines and serve as competitive antagonist. For example, Poxviruses.

Answer 413

Down-regulation of MHC class I pathway: Interfere with expression of MHC class-I molecules and inhibit antigen presentation.

Answer 414

 Vaccinia virus codes for a protein called VCP [Vaccinia Viral Protein], which binds to C4b, inhibiting classical complement pathway.  A glycoprotein component of Herpes Simplex virus bind to C3b, inhibiting both classical and alterative complement pathways.

Answer 415

Evasion of Neutralizing Antibodies:  Some viruses produce large amounts of soluble proteins that “soak up” antibody.  Variation in the viral antigens  Production of antibodies that are incapable of neutralization. Example: Caprine Arthritis-Encephalitis of goats.  Slow production of antibodies compared to fast infection of cells by virus.

Answer 416

Latency:  Although the viral genome is in host cell, transcription of viral genes that encode viral antigenic proteins (that are presented on surface of infected host cell with MHC-molecules) are blocked.  Integration of viral genome in host cell genome, example retroviruses.

Answer 417

Cell-to-Cell spread of viruses: Not exposed to host immune mediators (refer to lecture on virus replication, slides 74-75).

Answer 418

Inhibition of Apoptosis: Poxvirus and Herpesvirus produce caspase inhibitors that protect the infected cells against death and allow virus replication to be completed.

Answer 419

The study of the determinants, frequency, dynamics, and distribution of viral diseases in populations.

Answer 420

Porcine Epidemic Diarrhea Virus (PEDV) causes severe Diarrhea and Vomiting in Pigs. First identified in the United States in May 2013. By the end of January of 2014, PEDV spread quickly across many US states, causing severe economic losses.

Answer 421

The risk of infection and/or disease in an animal or animal population is determined by:  Characteristics of the virus (e.g., genetic variation from evolution)  The host and host population (e.g., passive, innate, and acquired resistance)  Behavioral, environmental, and ecological factors that affect virus transmission from one host to another

Answer 422

Epidemiology is an interdisciplinary field of science that takes into consideration all the above factors to provide data on the pattern, spread, occurrence and impact of a viral disease in a population, and also on the potential of occurrence of a viral disease in a population.

Answer 423

 To identify and/or clarify the role of viruses in the etiology of diseases  Understanding the interaction of viruses with environmental determinants of disease  In determining factors affecting host susceptibility  In unraveling modes of viral disease transmission  Studying the impacts of viral disease on health, economy and society  Studying role of infectious pathogens in the pathogenesis of chronic non- communicable diseases, such as oncogenic viruses in cancer  In large-scale testing of vaccines and drugs, i.e. clinical trials.

Answer 424

This diagram detailing SARS transmission in Singapore shows the important role of “super-spreaders” in transmitting the disease. Five people caused more than half of the 205 cases there.

Answer 425

Bats to civet to humans

Answer 426

The number [%] of deaths among the clinically ill animals

Answer 427

The number [%] of animals in a population that die from a particular disease over a specified period of time.

Answer 428

The morbidity rate is the percentage of animals in a population that develop clinical signs attributable to a particular virus over a defined period of time (commonly the duration of an outbreak).

Answer 429

The number of new cases that occur in a population over a specified period of time. The incidence rate, or attack rate, is a measure of the occurrence of infection or disease in a population over time—for example, a month or a year, and is especially useful for describing acute diseases of short duration.

Answer 430

The number of occurrences of disease [old and new cases], infection, or related attributes [antibodies] in a population, at a particular point of time. It is difficult to measure the incidence of chronic diseases. For such diseases it is customary to determine the prevalence—that is, the ratio, at a particular point in time, of the number of cases currently present in the population divided by the number of animals in the population.

Answer 431

Viral diseases occurring occasionally, singly, or in scattered instances, and in a irregular and haphazard manner.

Answer 432

The constant presence of a Viral disease within a given geographic area or population group.

Answer 433

The occurrence of more cases of Viral diseases than expected in a given area or among a specific group of people/animals over a particular period of time. Refers to peaks in disease incidence that exceed the endemic/ enzootic baseline or expected incidence of disease.

Answer 434

a virus epidemic occuring over a very wide area( several continents or countries) and usually affecting a large proportion of the population

Answer 435

Animals that have contracted an infectious viral disease, but display no clinical symptoms.  Shed virus, transmitting disease to others.  Shedding of virus may be continuous or intermittent.

Answer 436

Animals that shed virus during the incubation period of the disease.

Answer 437

Animals that shed virus during recovery from disease.

Answer 438

Carrier state may exist in an animal with an infection that is inapparent throughout its course.

Answer 439

* Zebras, Inapparent Carrier * Culicoides Vector * Healthy Horse bitten by Culicoides and become infected. *

Answer 440

A disease that is spread from one person or organism to another by direct or indirect contact.

Answer 441

refers to the time during which an infected animal sheds virus.

Answer 442

A disease not known to occur in a particular country or geographical area.

Answer 443

The habitat in which an infectious agent normally lives, grows and multiplies; reservoirs include human reservoirs, animals reservoirs, and environmental reservoirs. May be animate or inanimate.

Answer 444

The systematic collection, analysis, interpretation, and dissemination of health data on an ongoing basis, to gain knowledge of the pattern of disease occurrence and potential in a community, in order to control and prevent disease in the community.

Answer 445

Methods to study Epidemiology of Viruses  Seroepidemiology simply denotes the use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques.  Determine the prevalence or incidence of particular infections  Evaluate eradication and immunization programs  Assess the impact, dynamics, and geographic distribution of new, emerging, and re- emerging viruses.  Correlation of serologic data with clinical observations makes it possible to determine the ratio of clinical to subclinical infections  Study of duration of viral infection

Answer 446

The use of molecular biological data as the basis of epidemiological investigation of Viral Diseases.

Answer 447

In addition to general prevalence, crucial information on genetic diversity and origin of viruses. Important for identifying novel viruses, viral load in host, designing or judging efficacy of vaccines, developing diagnostics, and for conclusive evidence for transmission of viruses from animals to humans (Zoonosis) or vice versa

Answer 448

Defined as the spread of an infectious agent from one person/animal or group to another person/animal or group. ** Most viruses are transmitted by the horizontal route.** Contact, Vector, Airborne, Fomites, Vehicle borne, Iatrogenic

Answer 449

Spread of the infectious agent by direct or indirect contact

Answer 450

Direct-contact transmission involves actual physical contact between an infected animal and a susceptible animal (e.g., licking, rubbing, biting). This category also includes sexual contact , as seen in HIV or Herpesvirus infection.

Answer 451

Contact Transmission  Direct-Contact Transmission  Droplet Transmission: Transmission of virus in droplet nuclei (saliva or mucus) that travel less than 1 meter from the source to the susceptible host.  Sneezing, coughing, etc.  Due to short distance travel not considered as air-borne transmission.

Answer 452

Indirect-contact transmission occurs via fomites, such as shared eating containers, bedding, dander, restraint devices, vehicles, clothing, improperly sterilized surgical equipment, or improperly sterilized syringes or needles.

Answer 453

An inanimate object or substance that is contaminated with the infectious agent and is capable of transmitting infectious organisms from one individual to another.

Answer 454

Contact Transmission  Indirect-Contact Transmission:  Airborne transmission: Spread of infectious agents by droplet nuclei in dust that travel more than one meter, sometimes for miles, from the infected to the susceptible host. Droplets are small enough to remain in air for prolonged periods.

Answer 455

Also known as Arthropod-borne transmission. Arthropod vectors carry the viruses from the infected host to susceptible host.

Answer 456

Mosquitoes and other biting insects may serve as mechanical vectors for Fowlpox virus

Answer 457

 The arthropod vector acquires virus by feeding on the blood of a viremic animal.  Replication of the ingested virus, initially in the insect gut, and its spread to the salivary gland take several days. This period is known as extrinsic incubation period.  Virions in the salivary secretions of the vector are injected into new animal hosts during blood meals.  Helps virus to cross species barriers. Have you wondered why? When arthropods are active, arboviruses replicate alternately in vertebrate and invertebrate hosts. What happens to these viruses during the winter months in temperate climates when the arthropod vectors are inactive.

Answer 458

The survival of the virus from one ‘vector season’ to the next (period during which arthropods hibernate) is called “Overwintering” Important mechanisms for “overwintering” are transovarial and trans-stadial transmission.

Answer 459

The virus is transmitted from the mother tick through infected eggs to next generation of ticks.

Answer 460

The virus is transmitted from larva or nymph to next stage of development (nymph or adult). But not transmitted vertically (from mother tick to eggs and next generation). Example: tick-borne flaviviruses

Answer 461

Typical Mechanisms of Transmission of Arboviruses  Arboviruses: A class of viruses transmitted to humans by arthropods such as mosquitoes and ticks. The first two letters of the words arthropod' andborne, make up the 'arbo' that now designates this group of viruses as arthropod-borne.  Arboviruses are maintained in complex life cycles involving nonhuman primate/ vertebrate hosts and primary arthropod vectors.

Answer 462

 Types of Transmission Cycles:  Enzootic cycle (Sylvatic or Jungle cycle): The natural transmission of virus between wild animals/birds (vertebrate hosts) and primary insect vectors.  Epizootic cycle (rural cycle): The virus is transmitted between non-wild or domestic animals and the primary or accessory insect vectors.  Urban cycle: The virus cycles between humans and insect vectors

Answer 463

Amplifying host is in which the level of virus can become high enough that an insect vector such as a mosquito that feeds on it will probably become infectious.

Answer 464

Dead-end host or incidental host: a host from which infectious agents are not transmitted to other susceptible hosts. They do not develop sufficient viremia to be picked up by the insect vectors.

Answer 465

Bridge vector is an arthropod that acquires virus from an infected wild animal and subsequently transmits the agent to human or secondary host.

Answer 466

Enzootic and epizootic/epidemic transmission cycles of Western equine encephalitis virus (WEEV). WEEV is maintained in an enzootic cycle between passerine birds as reservoirs and its specific mosquito vector, C. tarsalis. Domestic and wild birds are considered important reservoir and epizootic amplifying hosts. It has also been suggested that lagomorphs and rodents can serve as amplification hosts. Other mosquito vectors include Aedes melanimon, C. stigmatosoma , Ae. vexans, Ae. dorsalis

Answer 467

Common-vehicle transmission includes fecal contamination of food and water supplies (fecal–oral transmission) and virus-contaminated meat or bone products [e.g., for the transmission of vesicular exanthema of swine, classical swine fever (hog cholera) and bovine spongiform encephalopathy].

Answer 468

 Iatrogenic transmission: Infection that is transferred during medical or surgical practice. This can happen in two ways:  Introduction of pathogens by contaminated instruments (non-sterile surgical instruments, syringes), or contaminated body surface (inadequate handwashing). Example: Spread of equine infectious anemia virus via multiple-use syringes and needles.  Introduction of pathogen through contaminated prophylactic or therapeutic preparations. Example: Presence of porcine circovirus genome in Rotavirus vaccine.

Answer 469

 Nosocomial transmission occurs while an animal is in a veterinary hospital or clinic. Also known as Hospital Acquired Infection. Example: During the peak of the canine parvovirus epidemic in the 1980s, many puppies became infected in veterinary hospitals and clinics.

Answer 470

The term “vertical transmission” is usually used to describe infection that is transferred from dam to embryo, or fetus, or newborn before, during, or shortly after parturition (colostrum, milk, or fecal contamination of teats)

Answer 471

 Early embryonic death or abortion (e.g., several lentiviruses)  Or may be associated with congenital disease (e.g., bovine viral diarrhea virus, border disease virus, porcine entero-virus),  Or the infection may be the cause of congenital defects (e.g., Akabane virus, bluetongue virus, feline parvovirus).

Answer 472

 Certain retroviruses are transmitted vertically via the integration of proviral DNA directly into the DNA of the germ line of the fertilized egg.  Cytomegaloviruses are often transmitted to the fetus via the placenta, whereas other herpesviruses are transmitted during passage through the birth canal.  Viruses are transmitted via colostrum and milk (e.g., caprine arthritis-encephalitis virus and maedi-visna virus of sheep).

Answer 473

 The physical stability of a virus affects its survival in the environment: Example: Viruses that are transmitted by the respiratory route have low environmental stability, whereas those transmitted by the fecal–oral route have a higher stability.  Population Size is crucial: A virus may disappear from a population if supply of susceptible hosts is exhausted. This depends on size of population, immunity and pattern of virus shedding.  Host Range: Many viruses can infect more than one host. Example, Foot and Mouth Disease Virus and Rotavirus.  Persistent Infections: Virus remains in host for long periods  Avoid exposure to external environment: Vertical Transmission, Venereal Transmission, Vector Transmission

Answer 474

Agglutination is a method using the property of specific antibodies to bind many antigens (antigens on pathogen, or antigen coated particles- latex beads) into single clumps thereby forming large complexes, which are easily precipitated. The precipitation can be macroscopically or microscopically visible.

Answer 475

The hemagglutination & Hemagglutination inhibition method relies on the property of some pathogens (mainly viruses) to nonspecifically agglutinate erythrocytes.

Answer 476

Examples: Hemagglutination inhibition test has been used extensively for detection of serotype specific antibodies against avian influenza & peste des petits ruminants (PPR).

Answer 477

Example: Detection of antibodies against avian influenza (matrix antibodies), equine infectious anaemia (Coggins test) and enzootic bovine leukosis.

Answer 478

Glycoproteins are inserted into host cell membrane at sites of budding of enveloped viruses. This allows monolayer cells to adsorb erythrocytes on their cell membranes. This phenomenon is known as hemadsorption.

Answer 479

• Infected monolayer cells are incubated with known specific antibody Antibodies bind to viral glycoproteins [spikes] in cell membrane • Attempts are made to wash away anti- bodies Antibodies remain bound to viral proteins • Pretreated monolayer cells are incu- bated with RBCs RBC binding is inhibited

Answer 480

 Neutralization of a virus is defined as the loss of infectivity through reaction of the virus with specific antibody.  Normally, the presence of unneutralized virus may be detected by reactions such as CPE, haemadsorption/haemagglutination, plaque formation, disease in animals.  However, when Virus and Serum (Antibodies) are mixed under appropriate condition and then inoculated into cell culture, eggs or animals. There is antigen-antibody reaction.  Antibody-bound virus (Neutralized) becomes non-infectious and cannot produce desired effects in eggs, cell-lines or animals.

Answer 481

Because IgM antibodies appear early after infection but drop to low levels within 1–2 months and generally disappear altogether within 3 months, they are usually indicative of recent infection.