Micro-Animal Viruses II
Terms
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- Broad categories of laboratory methods to confirm viral infection
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• Isolation and growth of virus
• Cytopathic effects in cells
• Electron microscopy to detect viral particles
• Detection of viral components (proteins, enzymes, nucleic acids)
• Evaluation of the patient’s immune response (serology) - give three ways in which viruses are cultivated
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1)Tissue culture
2)Embryonated egg
3) Intact animal - Give 3 methods for determinining infectious units of virus
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⬢ Plaque formation if virus lysis cells in tissue culture
⬢ Pock formation in membranes of chicken embryonated egg
⬢ Focus formation if virus causes proliferation of cells in tissue culture
⬢ Serial dilution end point method-looking for cytopathic changes in tissue culture
⬢ Serial dilution end point method, looking for characteristic symptoms in experimental animals - Consequences of viral infection
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Cell death and lysis
Proliferation of host cell(viruses often induce growth)
Fusion of membranes of adjacent cells- formation of multinucleate giant cells (found especially with viruses that have an F protein)
Inclusion bodies
Transformation- normal cells progress to malignant cancer cells with loss of contact
inhibition and uncontrolled proliferation - Give two ways in which viral particles are enumerated
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1) Electron microscopy
2) Hemagglutinin - Describe Hemagglutinin
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- some viruses (such as influenza viruses) are capable of binding to red blood cells.
⬢ Agglutinated red blood cells form a lattice that coats the well.
⬢ Unagglutinated red blood cells tumble to the bottom of the well and form a sharp button on the bottom of the well. - Give three ways of virus or viral products are observed
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immunological means
complement fixation
direct fluorescent antibody
Western blot radioimmunoassay
ELISA (Enzyme linked immunosorbant assay) - Give three examples of DNA Probes
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Southern blots- extracted DNA
In Situ hybridization- fix infected tissues and hybridize to radiolabeled probe.
PCR- polymerase chain reaction: Can find as few as 100 particles/ml of blood. Other methodologies to amplify target DNA to avoid PCR patent - How do we measure antibodies produced in response to animal viruses
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⬢ Neutralization of infectivity (these are usually antibodies produced to viral surface components)
⬢ Complement fixation
⬢ Hemagglutination-inhibition
⬢ Latex agglutination
⬢ ELISA
⬢ Indirect fluorescent antibody
⬢ Western immunoblot - Give 4 uses of testing for viral infection
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Diagnosis
Retrospective determination
Determine need for immunization
Establish infection - Describe diagnosis of viral infection
- usually requires acute and convalescent serum run simultaneously with a four fold rise in titer considered positive (2X rise not considered statistically significant). For some viruses it is possible to assay for high concentrations of IgM, which may indicate a recent primary infection.
- Describe retrospective determination-
- - if blood of individuals is stored, years later the cause of a an epidemic illness can be determined.
- Give 3 examples of immunity to viral infections
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-Virus neutralization by antibodies
-Cell-mediated immunity
-Interferons- inhibit viral multiplication and may provide temporary and localized protection for nearby cells.
-Natural Killer Cells
-Complement - Cytotoxic T-Cells
- A cell that is actively infected with virus can then process the endogenously produced viral antigens and present them to cytotoxic T-Cells. These T-cells are activated and are then produce cytotoxic substances.
- Unusual immune system reactions to a viral disease
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Immunological tolerance (little or no cell mediated immunity is induced)
Cell mediated response- in chronic hepatitis B carriers, the virus by itself causes little cell damage, but cytotoxic T cells kill some virus-infected cells causing liver damage.
Enhancing antibodies- Several Flaviviruses, the presence of some antibody to the virus enhances multiplication of the virus. - Patterns of pathogenesis of viral infections: Localized infections
- viral multiplication and cell damage localized near the site of entry
- Patterns of pathogenesis of viral infections: Disseminated infections
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1) Local multiplication at the site of entry.
2) Spread through the lymphatics to the blood stream and circulation in the blood. (primary viremia)
3) Multiplication at secondary sites
4) Secondary viremia
5) Infection of the target organ
Often the infection is asymptomatic through the first four steps. We call this the incubation period. - Inapparent Infections-
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-asymptomatic viral infections.
-very common, and may result from infection by attenuated virus or from effective host defense mechanisms. - Inapparent Infections are important because
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-They represent an often unrecognized source for dissemination of a virus
-And may confer immunity on the host - Latent infection-
- virus particles are not demonstrable, but reappear during recurrences. Viral nucleic acid is demonstrable, even between recurrences. (Herpesvirus infections are the best characterized examples.)
- Chronic infection-
- Virus is always demonstrable and often shed. (Hepatitis B infection is the best-characterized example.) Infected cells produces and release virus, but cellular metabolism is little affected and the infected cells can grow and divide.
- Cells infected with more than one viral particle from the same group can lead to:
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Recombination- due to homologous recombination
Reassortment- in viruses with segmented genomes (ie influenza)
Reactivation-either of the above can lead to the rescue of a marker on an inactivated particle by superinfection with a live virus particle or a virus particle inactivated in a different region. - Give 5 ways we can Control Viral Diseases
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Prevention of transmission
Public health surveillance
Education
Isolation of cases of diseases
Passive immunization
Active immunization- either live attenuated, inactivated, or subunit vaccines are used. - Live Attenuated Vaccines: Describe length of immunity, Ab response, & Cell mediated immunity
- length of immunity is MANY YEARS, Ab response is IGA & IGG, & Cell mediated immunity is GOOD
- Inactivated Vaccines: Describe length of immunity, Ab response, & Cell mediated immunity
- length of immunity is USUALLY LESS, Ab response is IGG, & Cell mediated immunity is POOR
- What is required to eliminate a virus from a population?
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-No animal reservoir
-Good vaccine
-Few or no subclinical cases (latent infections ensure that the virus will survive in the population)
-One antigenic type or only a few (no antigenic switching) - contributing factors to new viral diseases
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Political/Social/Environmental changes that increase human contact with an infected carrier or vector (HIV).
Genetic changes
-point mutations (Influenza, HIV)
-Intramolecular recombination
Genetic reassortment (Influenza) - A parasite needs to be ________. Therefore, Evolution favors________ .
- transmissible/transmissibility
- If viruses can infect a NEW host species, they tend to be _____ virulent than in a long-term host species.
- more