Block 4 Flashcards
2 defense mechanisms of respiratory tract
Mucociliary blanket
Temperature Gradient
Temperature Gradient
There is a temperature gradient between the nasal passage (33 C) and the alveoli (37) that plays an important role in the localization of infection. Thus, rhinoviruses, which infect the nasopharynx and caue 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.
Pattern Recognition Receptors (PRR)
viral surface receptors that recognize specific pathogen-associated molecular patterns (PAMPs), which are macromolecules present in virus and othe microbes, but not on host cell. One class of PRRs are Toll-like receptors (TLRs)
T/F Interferons show no virus specificity
True
T/F DNA viruses are stronger inducers of interferons than RNA Viruses
FALSE: RNA viruses are stronger inducers
How should interferons be administered to a patient?
Parenteral route (injection) because they are glycoproteins
Interferons
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 anticancer properties
IFN-a
Leukocyte interferon. Produced in large quantities by plasmacytoid dendritic cells
What produces Type II interferons?
Antigen-stimulated T cells and Natural Killer (NK) cells
IFN-B
Fibroblast interferon. Secreted by virus-infected fibroblast.
IFN-y
Only type of Type II Interferon
When are Type III interferons expressed?
In response to viral infections and activation of TLRs
3 types of Type III Interferons
k
Primary function of Type III interferons
Immunoregulator
Purpose of IFN-y
Mostly immunoregulatory (Type II)
What mediates humoral immunity
Antibodies released from B lymphocytes
What mediates cellular immunity
T lymphocytes
What elicits Cellular Mediated Immune (CMI) response? (2)
Internal viral antigens
Surface antigens (+ humoral response)
What can antibodies be directed against? (2)
1) Viral proteins on free virions (capsid or envelope)
2) Viral proteins expressed on surface of infected cell
Virus Neutralization
Neutralizing antibodies prevent virus attachment and entry into host cells. 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.
Antigenic Plasticity
Rapid changes in the structure of the viral antigen. May be result of mutation, resassortment or recombination.
Due to change in antigen structure, the virus may become resistant to immunity generated by previous infection.
Antigenic Multiplicity
Antigenic variants with little or no cross-reactivity
Virokines
Some viruses synthesize proteins which are homologs of cytokines/interferons
Viroceptors
Some viruses encode proteins that are homologous to the receptors for cytokines. Serves as a competitive agonist.
Virus epidemiology
The study of the determinants, frequency, dynamics, and distribution of viral diseases in populations
Case 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 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)
Incidence
The number of new cases that occur in a population over a specified period of time.
Incidence/Attack Rate
A measure of the occurence 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
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 diseases
Viral diseases occurring occasionally, singly, or in scattered instances, and in a irregular and haphazard manner
Enzootic 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 or among a specific roup 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 diseases (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.
Asymptomatic carrier
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.
Incubatory (acute) carriers
Animals that shed virus during the incubation period of the disease
Convalescent (chronic) carriers
Animals that shed 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
Period of contagiousness
Refers to the time during which an infected animal sheds virus
Exotic disease
A disease not known to occur in a particular country or geographical area
Seroepidemiology
Denotes the use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques
Molecular epidemiology of viruses
The use of molecular biological data as the basis of epidemiology investigation of viral disease
Horizontal (lateral) transmission
The spread of an infectious agent from one person/animal to another person/animal or group
Most viruses are transmitted by the ____ route
Horizontal
Contact transmission
Spread of the infectious agent by direct or indirect contact
Direct-Contact Transmission
Involves actual physical contact between an infected animal and a susceptible animal (ie licking, rubbing, biting). This category also includes sexual contact.
Droplet Transmission
A type of direct contact 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
Why is droplet transmission not considered as an air-borne disease?
Due to short travel distance
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
Fomite
An inanimate object or substance that is contaminated with the infectious agent and is capable of transmitting infectious organisms from one individual to another
Airborne transmission
A type of indirect-contact transmission.
The 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.
Vector Transmission / Arthropod-borne Transmission
Arthropod vectors carry the viruses from the infected host to susceptible host
Two types of vector transmission
Mechanical and Biological
Mechanical Transmission
Passive transport of the infectious agent on the feet or other body parts of the arthropod vector
Biological Transmission
Infectious agent undergoes either a necessary part of its life cycle, or multiplication, in the vector before transmission to susceptible host
What is the mechanical vector for Fowlpox virus?
Mosquitos and other biting insects
Transovarial Transmission
Type of biological transmission. The virus transmitted from the mother tick through infected eggs to next generation of ticks.
Trans-stadial Transmission
Type of biological transmission. The virus is transmitted from larva or nymph to next stage of development (nymph of adult). But not transmitted vertically (from other tick to eggs and next generation). Ex: tick-borne flaviviruses.
Arboviruses
A class of viruses transmitted to humans by arthropods such as mosquitos and ticks
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 human and insect vectors
Amplifying Host
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
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
An arthropod that acquires virus from an infected wil animal and subsequently transmits the agent to human or secondary host.
Common-vehicle transmission
Type of horizontal/lateral transmission.
Includes fecal contamination of food and water supplies (fecal-oral transmission) and virus-contaminated meat or bone products.
Latrogenic Transmission
Type of horizontal/lateral transmission.
Infection that is transferred during medical or surgical practice.
Two ways latrogenic transmission can happen
1) Introduction of pathogens by contaminated instruments (non-sterile surgical instruments, syringes), or contaminated body surface (inadequate hand washing). Ex: spread of equine infectious anemia virus via multiple-use syringes
2) Introduction of pathogen through contaminated prophylactic or therapeutic preparations
Nosocomial transmission / Hospital Acquired Infection
Occurs while an animal is in a veterinary hospital or clinic
Vertical transmission
To describe infection that is transferred from dam to embryo, or fetus, or newborn before, during, or shortly after partuition (colostrum, milk, or fecal contamination of teats)
Zoonosis
Infections that are transmissible from animals to humans
Do viruses transmitted by respiratory route or fecal-oral route have higher environmental stability
Fecal-oral route have higher environmental stability than respiratory route
Herd Immunity
A form of immunity that occurs when the vaccination of a significant large portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity.
Incubation Period
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.
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 appearance of the characteristic symptoms of disease
Acute Period
When the disease is at its height. Severe 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.
Risk group 1
No or low individual and community risk
Risk group 2
Moderate individual risk, low community risk
Risk group 3
High individual risk, low community risk.
A pathogen that usually causes serious human or animal disease but does not ordinarily spread from one infected individual to another. Effective treatment and preventative measures are available.
Risk group 4
High individual and community risk.
A pathogen that usually causes serious human or animal disease and that can be readily transmitted from one individual to another, directly or indirectly. Effective treatment and preventative measurers are not usually available.
What risk category is FMD in livestock?
Risk category 4
BSL-4
The maximum containment laboratory. They handle dangerous and exotic pathogens belonging to the highest risk group (ie risk group 4, ie ebola virus)
Qualities of BSL-4 Lab (4)
1) Negative air-pressure must be maintained in the laboratory room
2) Incoming and outgoing air should be HEPA-filtered (High Efficiency Particulate Air)
3) Sterilization through double door autoclaving system
4) Suit decontamination shower after leaving the containment laboratory area
Biohazard
Biological sybstances that pose a threat to the health of living organimss, primarily that of humans
Biosafety
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.
Aerosol
Very small droplets of fluid that can spread via air. Viruses can spread in lab through aerosol route.
Biosecurity
Laboratory biosecurity describes the protection, control, and accountability for valuable biological materials (VBM) within laboratories, in order to prevent their unauthorized access, loss, theft, misuse, diversion, or intentional release
Timing of sample collection for virus isolation
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.
Timing of sample collection for serological tests
Two blood specimens are generally collected – one during acute phase of the illness and the second sample during the convalescence period (varies upon type of virus, 10-14 days after 1st sample of even more)
Timing of sample collection for molecular diagnostics (ie PCR)
Obtained during the early parts of the illness
Viral Transport Medium (VTM)
Swabs
What do you do to prevent spillage while transporting infectious materials?
Basic triple packaging system
Electron Microscopy
Can be used to demonstrate viruses in samples and detect viruses that cannot be grown in-vitro
Negative-stain electron microscopy
1
2
3
Transmission electron microscope (TEM)
The method used in TEM is based on transmitted electrons. TEM seeks to see what is inside or beyond the surface
SEM
The method used in SEM is based on scattered electrons. SEM focuses on the sample’s surface and its composition.
Advantages of TEM over SEM (2)
TEM can produce images that have higher magnification and greater resolution than SEM
Advantages of SEM over TEM (1)
SEM produces 3D images while TEM only produces 2D images.
Assay
Qualitative or quantitative measuremtn of a target entity/analyte, such as drug of 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
Sensitivity
The probability (%) that cases with the infection (determined by the result of reference or ‘gold standard’ test) will have a positive result using the test under evaluation.
Specificity
The probability (%) that cases without the infection (determined by the result of reference or ‘gold standard’ test) will have a negative result using the test under evaluation.
Serum
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. (Red-top vacutainer tube)
Plasma
Is produced when whole blood is collected in tubes that are treated with an anticoagulant. The blood does not clot in the plasma tube (Lavender-top EDTA Vacutainer Tube)
