Exam 1 Terminology Flashcards
Virology
The study of viruses and viral diseases
Virologist
Someone who studies viruses
Virion
A complete virus particles that consists of an RNA or DNA core with a protein coat sometimes with external envelopes and that is the extracellular infective form of a virus.
Virus
Is a broad general terminology that is used to describe any aspect of the infectious agent and includes: the infectious (virion) or inactivated virus particles, or viral nucleic acid and protein in the infected cell.
Viroid
An infectious particle smaller than any of the known viruses, an agent of certain plant diseases. The particle consists only of an extremely small circular RNA (ribonucleic acid) molecule, lacking the protein coat of a virus.
Smallest viruses
Porcine circovirus type 1 (17 nm diameter)
Parvoviruses (18 nm diameter)
Largest viruses
Pandoravirus (400 nm diameter)
Poxvirus (200 nm) diameter and 300 nm in length)
Pleomorphism
The ability of some virus to alter their shape or size
Electron Microscopy (EM)
Requires negative staining with electron dense material. Resolution range is usually 50-75 angstroms.
Cryo-electrom Microscopy (Cryo-EM)
Allows the observation of biological specimens in their native environment (not stained or fixed in any way) at cryogenic temperatures in EM.
X-ray Crystallographic Method
The virus is crystallized. Then you bombarded the virus crystal with x-rays. The x-rays will strike and be reflected. Can measure angle of reflection and intensity of reflection. Fit into the computer and with software can reconstruct the virus structure.
Capsid
A protein (coat) shell of a virus that encases/envelopes the viral nucleic acid or genome
Capsomeres
Make up a capsid by non-covalent bonds. It is the basic subunit protein in the capsid of a virus.
Nucleocapsid
Capsid + virus nucleic acid
Triangulation number (T-number)
Described 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.
T-number formula
T = (h^2 + h * k + k^2)
Glycoprotein
Spike embedded on the envelope. Anchored in the lipid bilayer by means of hydrophobic bonds. Transmembrane proteins.
Matrix protein
Between the lipid envelope and the capsid. These proteins link the internal nucleocapsid to the lipid membrane envelope.
External glycoprotein
Anchored in the envelope by a single transmembrane domain, and a short internal tail. Usually major antigens.
Hemagglutinin (HA)
Binding, fusion, antigenic, hemagglutination, clumping RBC
Neuraminidase (NP)
Release progeny virus from host cell, antigenic
Channel proteins
Which are most hydrophobic proteins that form a protein lined channel through the envelope. Alters permeability of the membrane.
Fusion proteins
Fuse to host cytoplasmic membrane. Facilitates virus into the host cell. Host cytoplasmic membrane and virus envelope is fused. Needed to penetrate into the host cell.
Positive sense RNA genome
It is similar to mRNA and thus can be immediately translated by the host cell and can directly synthesize viral proteins.
Negative sense RNA genome
Is complementary to mRNA and must be converted to positive sense RNA by an RNS polymerase before translation.
Antigenic Drift
Caused by point mutations. Mutation is a change of nucleotide of the genome. There is a change of antigenicity of the virus as a result of point mutation.
Antigenic Shift - Recombination
Intramolecular recombination involves the exchange of nucleotide sequences between different nucleotides. Usually by closely related, viruses during replication.
Antigenic Shift - Reassortment
Is the most important mechanism for high genetic diversity in viruses with segmented genome.
Lysins
Hydrolytic enzymes produced by bacteriophages to cleave the host’s cell wall
Retroviral integrase (IN)
Enzyme produced by a retrovirus (such as HIV) that enables its genetic material to be integrated into the DNA of the infected cells
Reverse Transcriptase (RT)
Enzyme used to generate complementary DNA (cDNA) from a RNA template
Nucleic acid polymerase
viral genome replication
Neuraminidases
Enzymes that cleave glycosidic bonds. Allows release of viruses from host cell.
Incomplete virions
Virion without nucleic acid (empty capsid)
Defective virions
a virus that cannot replicate because it lacks a full complement/copy of viral genes.
Defective Interfering Particle (DIP)
When the defective viruses cannot replicate, but can interfere other congeneric mature virion entering the cells, we call them defective interfering particles (DIP)
Pseudovirion
Contains non-viral genome within the viral capsid, such as host nucleic acid instead of viral nucleic acid. Look like ordinary viral particles under EM, but do not replicate.
Pseudotypes
When related viruses infect the same cell, the genome of one virus may be enclosed in the heterologous capsid of the second virus.
The Baltimore Classification System
Is a classification system based on viral genome. Viruses are classified into one of the seven groups depending on combination of their nucleic acid (DNA or RNA), strandness, sense, and method replication.
The International Committee Taxonomy of Viruses (ICTV) Classification System
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. Considers: nature of virus genome and virus genetic diversity, virus replication strategies, and virus morphology.
Monolayer cultures
When the bottom of the culture vessel is covered with a continuous layer of cells, usually one cell in thickness
Primary Cell Culture
Growth of cells dissociated directly from the parental tissue. Cells have the same chromosomes and same number of chromosomes as the original tissue.
Secondary (Transfer) Cell Culture
When a primary culture is sub-cultured. This is periodically required to provide fresh nutrients and growing space for continuously growing cell lines.
Finite/Diploid Cell Lines
Homogenous population of a single cell type - fewer cell types. Derived mainly from embryos; or from secondary cell culture. Cells retain original morphology and diploid chromosome number. Growth rate is slow.
Continuous Cell Lines
Divide indefinitely. Derived directly from cancer cells; or induce transformation of a primary of diploid cell strain to divide indefinitely. Abnormal morphology and chromosome number. FDA prohibits their use in vaccine production.
Phenol Red pH Indicator
Red is normal color, at a pH of 7-7.5. If there is an accumulation of toxic substances in medium then it will become acidic and it will become yellow or orange in color.
Carbon Dioxide (CO2) Level
Changes in 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.
How will you dissociate/deattach adherent cells?
Use enzyme trypsin which is a proteolytic enzyme and cause lysis of adhesion factors. Or use integrins which rely on calcium
Cytopathogenic Effect (CPE)
Refers to damage or morphological changes to host cells during virus invasion
Shell vial
Small borosilicate glass vial with a coverslip. Grow cells in coverslip or shell vial. Inoculate the virus into the vial. Virus grows in monolayers. Take cover slip out and drip it with fluorescent antibody and look under the microscope.
Cultivation of viruses in eggs
Egg candling and egg inoculation
When can you not use eggs for experiments?
If there is a crack in the eggshell, infertile egg, and blood ring indicated early embryonic death
Routes of egg inoculation
- Chorioallantoic membrane inoculation
- Amniotic inoculation
- Allantoic inoculation
- Yolk Sac inoculation
Yolk Sac Inoculation
Drill hole (use 22 gauge), place the inoculum below the embryo and within the yolk material. Seal the hole in the eggshell with scotch tape or melted wax.
Allantoic Cavity Inoculation
26 gauge, drill hole in eggshell above or over the air sac. Inoculate specimen into the allantoic cavity.
Amniotic Cavity Inoculation
26 gauge, drill a hole in the egg shell over the air sac, inoculate specimen into the amniotic cavity.
Chorioallantoic Membrane Inoculation (CAM)
Drill two holes in the eggshell, one on the side and the other above the air sac. Move air sac to the side of the egg by gentle suction, using a rubber bulb. Inoculate specimen on the dropped CAM.
Pocks on CAM
Most common lesions found in eggs. Assay is known as pocks assay. Pocks formed by vaccine virus on CAM.
Ultracentrifuge
Provide sufficient gravitational force to efficiently sediment even the smallest viruses
Rate-zonal centrifugation
Narrow zone on the top of a density gradient. Under centrifugal force, particles move at different rates depending on their mass.
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 a particle equals that of the surrounding density gradient medium.
Isopycnic Centrifugation
Particles are separated solely on the basis of their buoyant density. Particles will never sediment to the bottom of the tube. Virus particles appear as visible bands.
Virus Purification with Membrane Chromatography
Chromatography membranes are not 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 elation of viruses can be achieved by anion and cation exchange membranes.
Virus Quantification
Counts the number of viruses in a specific volume to determine the virus concentration
Virus Titer
The lowest concentration of virus that still infects cells
Biological - Viral Quantification Tests
Depend on a virus particle initiating a successful replication cycle. Plaque assays, pock assays, various endpoint titration methods.
Physical - Viral Quantification Tests
Do not depend on any biological activity of the virus particle. More related on the counting. EM, Hemagglutination, ELISA, PCR, flow cytometry.
Transmission Electron Microscopy (TEM)
Direct particle counts; the most direct method to determine the concentration of virus particles in a sample.
Virus Counter 2100
The technology behind the virus counter 2100 is based on 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
Hemagglutination Assay
Antigen concentration assessment. RBC in suspension becomes linked (agglutinated) by ND virus receptors. RBC settle to form a mat.
High Performance Liquid Chromatographhy (HPLC)
Antigen concentration assessment. The concentrations of specific viral antigens may be quantified through UV analysis of fractions generated during HPLC.
Single Radial Immunodiffusion (SRID)
Antigen concentration assessment. Radial diffusion of purified viral antigens (standards) and viral particles through agarose gel seeded with polyclonal antisera against a viral antigen.
Monolayer Plaque Assay
A circular zone of white necrotic cells surrounded by viable cells in a monolayer. It is a functional measurement, and has no relation to actual number of viruses.
Plaque Forming Units/ml (PFU)
Measures the number of virus particles capable of forming plaques per unit volume.
Transformation Assay
Quantitative determination of titers of oncogenic viruses. Oncogenic viruses transform cells in culture. Transformed cells lose contact inhibition and become heaped upon one another.
Quantal Assay
Measures the presence of absence of infection. Use for certain viruses that do not form plaques or for determining the virulence of a virus in animals or eggs.
Lethal dose 50
Amount of virus that kills 50% of test subjects
TCID50
A Tissue Culture Infectious Dose which will infect 50% of the cell monolayers challenged with the defined inoculum
Multiplicity of Infection (MOI)
Is the average number of virus particles infecting each cell
TCID50 Formula
(% Infection above 50% - 50%)/ (% Infection above 50% - % Infection below 50%)
Permissive Cell
A cell in which a virus is able to replicate
Non-permissive cell
Cells in which a factor or factors necessary to viral reproduction is not present or one detrimental to viral reproduction is present
One-step Virus Growth Curve
- Viral adsorption and entry
- Viral uncoating and replication
- Viral maturation
- Viral release
Burst Size
Number of infectious virions released per average cell
Adsorption
During this period, virus attached to and enters cells, and the titer of free virus in the medium may actually decline
Eclipse Period
Tie interval between uncoating (“disapperance” of viruses) and appearance, intracellularly, of first infectious progeny virion.
Latent Period
The time before new infectious virus appears in the medium. I.e., from uncoating to just prior to the release of the first extracellular virions.
Steps of Virus Replication
- Attachment (adsoprtion)
- Penetration (Injection)
- Uncoating
- Synthesis of viral components (nucleic acid and protein)
- Assembly and maturation
- Release in large numbers (lysis)
Co-receptor
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.
Endocytosis
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 non-specific internalization of molecules.
Surface Fusion
Type of virus penetration. Only enveloped viruses. Membrane fusion or fusion proteins facilitates membrane fusion.
pH dependent surface fusion and uncoating
Low pH in endosome promotes fusion of envelope with endosomal membrane; lysis of nucleocapsid by lysosomal proteases, and release of viral genome
pH independent surface fusion and uncoating
The F protein catalyzes membrane fusion at the cell surface at neutral pH. The viral nucleocapsid is then released into the cytoplasm.
Pore-mediated penetration
Penetration of viral genome into host cell (non-enveloped aka naked viruses). Inject their genome into the host cytoplasm through creation of a pore in the host membrane.
Antibody-mediated penetration
Antibody (Ig - Fc) receptor enhances the entry of viruses into host cell
Capping
Addition of 7-methylguanosine of the 5’ end of RNA. Provides stability, binding of mRNA to ribosomes, and mark mRNA as “self”.
3’-Polyadenylation
Viral mRNAs can be polyadenylated by host or viral enzymes. A stretch of adenylated residues are added to the 3’ end.
Splicing
RNA splicing is a process that removes introns and joins exons in a primary transcript
Exon
the portion of a gene that codes of amino acids
Intron
a portion of a gene that does not code for amino acids
Constituitive splicing
Every intron is spliced out; every exon is spliced in
Alternative splicing
All introns spliced out; only selected exons spliced in. Results in mRNAs having different coding information derived from a single gene
Monocistronic
A type of viral mRNA that encodes one polypeptide. Singe RNA that will encode one protein.
Polycistronic
A type of viral mRNA that encodes several polypeptides.
Exocytosis
By budding through the membrane of golgi apparatus or ER. Vesicles containing the virus then migrate to the plasma membrane and are released by exocytosis
Extracellular Spread
Released viruses in extracellular environment. Travel to a new cell. Infect new host cell. Same replication cycle repeated etc.
Intercellular Spread
Spread from cell-to-cell without contact with extracellular environment. Results in rapid virus dissemination, evasion of immune system and persistent infections
Disseminated infection
Infection spreads beyond the primary site of infection
Systemic infection
If a number of organs or tissues are infected
Viremia
The presence of a virus in the blood. Virus may be free in the blood or in a cell.
Passive viremia
Direct inoculation of virus in the blood. Bite of arthropods or contaminated syringe
Primary viremia
Initial entry of virus into the blood after infection
Secondary viremia
Virus has replicated in major organs and once more entered the circulation
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
Neurotropic virus
Viruses that can infect neural cells. Infection may occur by neural or hematogenous spread.
Neuroinvasive virus
Viruses that enter the central nervous system (spinal cord and brain) after infection or a peripheral site.
Neurovirulent virus
Viruses that cause disease of nervous tissue, manifested by neurological symptoms and often death.
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.
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.
Centripetal Movement of Virus
Towards to the CNS/Brain
Centrifugal Movement
From CNS, within peripheral nerves, to other location in body
Acute Infection
Usually intensive shedding over a short period of time
Persistent Infection
Can be shed at lower titers for months to years
Tropism
The specificity/affinity of a virus for a particular host tissue
Pantropic Viruses
Can replicate in more than one host organ/tissue
Viral Enhancers
Gene activators that increase the efficiency of transcription of viral or cellular genes, facilitating virus replication
Vesicles
Small distinct elevation with fluid
Ulcers
Opening in the skin caused by sloughing of necrotic tissue, extending past the epidermis
Nodules
Palpable, solid, elevated mass nodules with distinct border, tumors extending past the epidermis
Warts
Are benign (not cancerous) skin growths that appear when a virus infects the top layer of the skin
Papules
Papular stomatitis in cattle
Erythema
Redding of skin, consequence of systemic viral infections (endothelial injury in blood vessels throughout body, including those of the subcutaneous tissues)
Viral-bacterial synergism
When virus and bacteria cause more harm together then they would alone
Progressive Demyelination
Without the myelin sheath the nerve signals are not delivered properly. Will find seizures as a common sign.
Petechiae Hemorrhage
pinpoint hemorrhage
Ecchymoses
large areas of hemorrhage with ill defined margins
Disseminated Intravascular Coagulation (DIC)
Widespread activation of the clotting cascade that results in the formation of blood clots in the small blood vessels througout the body
Teratogenesis
The abnormal development of arrests in development of the embryo or fetus. Results in death or malformation.
Virus Induced Immunopathology
Tissue injury mediated by host immune response to virus infection.
Immunopathology
is often the cause of damage with viruses that are relatively non-cytolytic and persistent
Cytokines
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.
Monokines
cytokines produced by mononuclear phagocytic cells
Lymphokines
cytokines produced by activated lymphocytes, especially Th cell
Interleukin
cytokines that act as mediators between leukocytes
Infectious bursal disease
Virus replication causes atrophy of the bursa and a severe deficiency of B lymphocytes, resulting in immunosuppression.
Latent (persistent) infection
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
Chronic (persistent) infection
Virus is continuously shed from or is present in infected tissue. Established host immunity is unable to clear virus from acute infection.
Slow (persistent) infection
Prolonged incubation period, lasting months or years
Primary CPE
Induced by viral replication and viral proteins toxic to host cells
Secondary CPE
effects of metabolic needs of the virus
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.
Subtotal destruction of cell
consists of detachment (death) of some, but not all of the cells in the monolayer.
Focal destruction of cells
produce localized areas (foci) of infection
Pyknosis
degenerative condition of a cell nucleus marked by clumping of the chromosomes, hyperchromatism, and shrinking of the nucleus.
Cell fusion (synctium or polykaryon formation)
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.
Inclusion bodies
An abnormal structure in a cell nucleus or cytoplasm or both
Negri bodies
Consists of ribonuclear proteins produced by the rabies virus
The intrinsic pathway
the mitochondrial pathway is activated as a result of increased permeability of mitochondrial membranes subsequent to cell injury, such as the associated with viral infection
The extrinsic pathway
the death receptor pathway is activated by engagement of specific cell-membrane receptors, which are members of the TNF receptor family.
Non-cytocidal Viruses
Usually do not cause immediate death of cells in which they replicate. They often cause persistent infection.
Cell Transformation
Is the changing of a normal cell into a cancer cell
Neoplasia
Is descriptive term that denotes an abnormal tissue overgrowth that may be either localized of disseminated. It is the process that leads to the formation of neoplasms (syn. Carcinogenesis)
Oncology
study of neoplasia and neoplasms
Benign Neoplasm
Is a growth produced by abnormal cell proliferation that remains localized and does not invade adjacent tissue
Malignant Neoplasm
(Syn. Cancer) is locally invasive and may also be spread to other parts of the body (metastasis)
Oncogenic viruses:
Viruses that cause or give rise to tumors
Neoplasms (tumors)
Arise as a consequence of the dysregulated growth of cells derived from a single, genetically altered progenitor cell
Metastatsis
Is the spread of cancer cells from the part of the body where it started (the primary site) to the other parts of the body.
Proto-oncogenes
are often involved in growth signaling and anti-apoptotic pathways
Oncogenes
Mutated forms of proto-oncogenes or aberrantly expressed proto-oncogenes. Function in an unregulated manner.
Tumor Suppressor Genes
encode proteins that inhibit cell proliferation (by holding cell cycle at G1 phase)
Rb: Retinoblastoma Protein
Tumor suppressor protein, alternates between phosphorylated and unphosphorylated state. The role of un-phosphorylated Rb is to bind to the transcription factor E2F, not allowing cell division to procee from G1 to S phase. Phosphorylated Rb cannot bind E2F from its inhibition and allows the cell cycle to progress
P53 Protein
P53 activates the DNA repair system and stops the cell cycle at the G1 checkpoint (before DNA replication)
Productive Infection in Permissive Cell
The virus completes its replication cycle, resulting in cell lysis
Non-productive infection in Non-permissive cell
The virus transforms the cell without completing its replication cycle
C-onc genes/proto-oncogenes
Are host genes that encode important cell signaling products that regulate normal cell proliferation
V-onc genes
Separated from the cellular machinery that normally controls gene expression (lacks introns), so they have power of unregulated expression
Slow/chronic transforming retrovirus
Integration of retroviral genes into host chromosomal DNA can occur at promoter or enhancer sites that drives the increase in proto-oncogene/C-onc gene expression, leading to malignant transformation of the cell
Promoter
DNA sequence at which DNA-dep RNA polymerase binds to initiate transcription
Enhancer
A transcriptional regulatory sequence located some distance from the promoter; it increases the rate of initiation of transcription
Perforin
Can produce pores in plasma membranes
Granzymes
Proteins that can initiate apoptosis
Granulocytosis
Presence in peripheral blood of an increased number of granulocytes, i.e. Neutrophils, eosinophils, basophils, mast cell
Virus neutralization
Neutralizing antibodies prevent virus attachment and entry into host cell. They bind to the viral capsid or host envelope
Opsonization
Coating of virions with antibodies. Antibody coated virion is recognized and phagocytosed by macrophages and sometimes by neutrophils
Clumping of viruses (Immunocomplex formation)
Reduced the number of viral particles available for cell invasion
Activation of Complement System
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)
Antigenic plasticity
Rapid changes in the structure of the viral antigen. May be the result of mutation, reassortment or recombination
Antigen multiplicity
Antigenic variants with little or not cross-reactivit
Negative Cytokines Regulation
Blocking interferon receptor signal
Virokines
Some viruses synthesize proteins which are homologs of cytokines/interferons.
Viroreceptors
Some viruses encode proteins that are homologs bind to cytokines and serve as competitive antagonist.
Virus Epidemiology
The study of determinants, frequency, dynamics, and distribution of viral disease in populations
Cast-fatality rate
The number (%) of deaths among the clinically ill animals
Mortality rate
The number (%) of animals in a population that die from a particular disease over a specified period of time
Morbidity rate
The % 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)
Incidence
The number of new cases that occur in a population over a specified period time
Incidence rate or attack rate
a measure of occurrence of infection or disease in a population over time
Prevalence
The number of occurrences of disease (old and new cases), infection, or related attributes (antibodies) in a population, at a particular point of time
Sporadic viral disease
Viral diseases occurring occasionally, singly, or in scattered instances, and in an irregular and haphazard manner
Enzoonotic viral diseases
(endemic in humans), the constant presence of a viral disease within a given geographic area or population group
Epizootic viral diseases
(epidemic in humans), the occurrence of more cases of viral diseases than expected in a given area of 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
Panzootic viral disease
(pandemic in humans), a virus epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population
Carrier
Animals that have contracted an infectious viral disease but display no clinical symptoms
Incubatory (acute) carriers
Animals that shed virus during the incubation period of the disease
Convalescent (chronic) carriers
Animals that shed the virus during recovery from disease
Inapparent carriers
Carrier state may exist in an animal with an infection that is inapparent throughout its course
Contagious disease
A disease that is spread from one person or organism to another by direct or indirect contact
Reservoir
The habitat in which an infectious agent normally lives, grows or multiplies; reservoirs include human reservoirs, animal reservoirs, and environmental reservoirs. May be animate or inanimate
Surveillance
The systematic collection, analysis, interpretation, an 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
Direct-contact transmission
involves actual physical contact between an infected animal and a susceptible animals (e.g. licking, rubbing, biting). STDs.
Droplet transmission
Direct-contact, transmission of virus in droplet nuclei (saliva or mucus) that travel less than 1 meter from the source to the susceptible host
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
Fomites
An inanimate object or substance that is contaminated with the infectious agent and is capable of transmitting infectious organism from one individual to another
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
Mechanical transmission - passive transmision
infectious agent undergoes either a necessary part of its life cycle
Biological transmission
infectious agent undergoes either a necessary part of its life cycle before transmission
Extrinsic incubation period
replication of the ingested virus, initially in the insect gut, and its spread to the salivary gland takes several days
Overwintering
the survival of the virus from one vector season to the next (period during which arthropods hibernate)
Trans-ovarial transmission
The virus is transmitted from the mother tick through infected eggs to the next generation of ticks
Trans-stadial transmission
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)
Arboviruses
A class of viruses transmitted to humans by arthropods such as mosquitoes and ticks.
Enzoonotic cycle (sylvatic or jungle cycle)
the natural transmission of virus betwen 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
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
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
Bridge vector
Is an arthropod that acquires virus from an infected wild animal and subsequently transmits the agent to human or secondary host
Common Vehicle Transmission
Includes fecal contamination of food and water supplies and virus contaminated meat or bone products
Iatrogenic Transmission
Infection that is transferred during medical or surgical practice
Nosocomial transmission
Occurs while an animal is in a veterinary hostpital or clinic
Vertical transmission
Infection that is transferred rfom dam to embryo or fetus, or newborn before, during, or shortly after parturition (colostrum, milk, or fecal contamination of teats)
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
Herd Immunity
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
Incubation period
refers to the internal between infection and the onset of clinical signs. In many diseases there is a period during which animals are infectious before they become sick
Prodromal period
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 appearnce of the characteristic symptoms of the disease
Acute period
when the disease is at its height. Sever clinical signs
Decline period
period when clinical signs begin to subside
Convalescent period
the body gradually returns to its pre-diseased state and health is restored
Biohazard
Biological substances that pose a threat to the health of living organisms, primarily that of humans
Biosafety
Laboratory biosafety described the containment principles technologies and practices that are implemented to prevent the unintentional exposure to pathogens and toxins, or their accidental release
Aerosol
Very small droplets of fluid that can spread via air. Viruses can spread in lab through aerosol route
Biosafety Cabinets (BSC)
An enclosed, ventilated laboratory workspace for safely working with materials contaminated with (or potentially contaminated with pathogens requiring a defined biosafety level)
Biosecurity
Laboratory biosecurity described the protection, control and accountability for valuable biological materials within laboratories, in order to prevent their unauthorized access, loss, theft, misuse, diversion or intentional release
Virus isolation sampling
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
Serological test sampling
Two blood specimens are generally collected - one during the convalescence period
Molecular diagnostics sampling
Obtained during the early part of illness
Viral Transport Medium (VTM)
Prevents specimen from drying, help maintain viral viability and retards the growth of microbial contaminants. Consts of a buffered salt solution to which has been added protein and antimicrobials
Negative Stain Electron Microscopy
Following bombardment with an electron beam, the stain absorbs electrons in much higher amounts than the sample. 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
Transmission Electron Microscope (TEM)
Based on transmitted electrons. Seeks to see what is inside or beyond the surface
Scanning Electron Microscope (SEM)
Based on scattered electrons, focuses on the sample’s surface and its composition. Produces 3D images.
Assay
Qualitative or quantitative measurement of a target entity/analyte, such as a drug or biomolecule
Gold Standard Test
A diagnostic test that is considered to be the most accurate and best available under a particular condition or set of conditions
Negative Predictive Value (NPV)
the probability that a negative test result accuraetly indicates the abscence of infection
Sensitivity
The probability (percentage) that cases with the infection (determined by the result of the reference of “gold standard test”) will have a positive result using the test under evaluation
Specificity
The probability (percentage) that cases without the infection (determined by the result of the reference of “gold standards test”) will have a negative result using the test under evaluation
Positive Predictive Value (PPV)
The probability of a positive result accurately indicating the presence of infection
Serum
The clear yellowish fluid obtained upon separating whole blood into its solid and liquid components after it has been allowed to clot. Plasma - clotting factors = serum.
Collection of plasma
Plasma is produced when whole blood is collected in tubes that are treated with 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.
Typical ELISA
Enzyme tagged to antibody which is bound to antigen will change color of substrate. Intensity of color indicates more positive reaction
Direct ELISA
Antigens are immobilized and enzyme conjugated primary antibodies are used to detect or quantify antigen concentration. The specificity of the primary antibodies that recognize the primary antibodies.
Indirect ELISA
Primary antibodies are not labeled, but detected instead with enzyme - conjugates secondary antibodies that recognize the primary antibodies
Sandwich ELISA
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
Competitive ELISA
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. 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”). A substrate is added, and remaining enzymes elicit a chromogenic of fluorescent signal. Weaker signal indicates presence of antigens in sample.
Fluorescence Antibody Test (FAT)
The antibodies are labelled with a fluorescent dye (most commonly used in fluorescent isothiocyanate) [FITC] or rhodamine). Visible fluorescence appears following Ag-Ab reaction.
Direct FAT
Labelled antibodies are added onto the sample (antigen). Visible fluorescence appears at the binding sites of the specific antibodies (antigen-antibody binding).
Indirect FAT
IFAT employs a secondary antibody labeled with a fluorescent marker that recognizes the primary antibody bound to antigen
Immunohistochemistry
The antibody is tagged with an 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.
Immunohistochemistry Direct Assay
Enzyme tagged with primary antibody that binds to antigen. Upon successful antigen-antibody binding, tagged enzyme catalyzes substrate to produce color product.
Immunohistochemistry Indirect Assay
Enzyme tagged to a secondary antibody that is specific against primary antibody
Immunochromatography (lateral flow devices)
A form of POC test that is simple to perform, easy to carry, and does not require specialized equipment. Antibodies on the chromatographic paper, 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. Resulting in generating a colored red purple line. Indicates the presence of antigen of interest in the sample.
Point of Care (POC)
Diagnostic testing performed at or near the patient’s site of care
Agglutination
Using the property of specific antibodies to bind to many antigens into a single clumps thereby forming large complexes, which are easily precipitated
Hemagglutination and Hemagglutination inhibition test
relies on the property of some pathogens (mainly viruses) to non-specifically agglutinate erythrocytes
Agar gel immunodiffusion test
Performed in petri dish with agar. Take a petri dish and make two wells. One well you supply antigen in other well you load antibody this antigen and antibody will diffuse toward each other. If it correspond to the antibody it will produce a white line also known as antibody antigenic precipitate
Complement Fixation Test - POSITIVE REACTION
Serum from patient has Ab against Virus A. Add ready made Virus A Ag. Ab will bind to Ag A. Add complement which will bind to the Ag-Ab complex. As a result free complement is not available. Add sheep RBC and anti-sheep RBC Ab complement is available to mediate hemolysis of sheep RBC. Intact sheep RBC settle at bottom of well.
Complement Fixation Test - NEGATIVE REACTION
Serum from patient is negative to Virus A, it will have no Ab. We add ready made virus A Ag. Viral Ag is free as no Ab is present. Add complement, it will also be free as there is no Ag-Ab complex to bind to. Add sheep RBC and anti-sheep RBC Ab. Free complement is available and mediates hemolysis of sheep RBC. Find the hemolysis of sheep RBC.
Immunoblotting
Run a sample in verticle gel and that will separate different proteins based on molecular weight. Transfer to nitrocellulose membrane from the gel. Treat it with Ab. Specific Ag bind to corresponding labelled Ab we get dark bands visualized.
Hemadsorption
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.
Hemadsorption - Inhibition Assay
Infected monolayer cells are incubated with known specific Ab. Abs bind to viral glycoproteins (spikes) in cell membrane. Attempts are made to wash away antibodies. Antibodies remain bound to viral proteins. Pretreated monolayer cells are incubated with RBCs. RBC binding is inhibited.
Neutralization Assays
Loss of infectivity through reaction of the virus with specific Ab. Presence of unneutralized virus may be detected by reactions such as CPE, hemadsorption/hemagglutination, plaque formation disease in animal. Ab-bound virus (neutralized) becomes non-infectious and cannot produce desired effects in eggs, cell-lines or animals.
IgM class-specific antibody assay
Because IgM antibodies appear early after infection by drop to low levels within 1-2 months and generally disappear altogether within 3 months, they are usually indicative of recent infection
