Virological Methods- Saviola

Question 1

What are the 5 types of viral infections?

Answer 1

Localized, Disseminated, Inapparent, acute, Persistent (latent, chronic)

Question 2

Define localized infection and give an example.

Answer 2

infection localized to site of entry (example: HSV).

Question 3

Define Disseminated infection and give an example.

Answer 3

• Local multiplication at the site of entry.
• Spread through the lymphatics to the blood stream and circulation in the blood. (Primary viremia)
• Multiplication at secondary sites.
• Secondary viremia.
• Infection of the target organ.
Example: varicella-zoster virus (VZV)

Question 4

Define Inapparent infection.

Answer 4

asymptomatic viral infections.

Question 5

Define Acute infection.

Answer 5

virus infects host, shortly after disease ensues. Symptoms gone pretty soon after. The virus can hide and develop into persistent infection.

Question 6

Define the 2 types of persistent infection and give an example of each.

Answer 6

1. Latent infection-virus particles are not demonstrable, but reappear during recurrences. Viral nucleic acid is demonstrable, even between recurrences. (Ex: Herpes virus)
2. Chronic infection- Virus is always demonstrable and often shed. (Ex: Hepatitis B)
   Infected cells produce and release virus, but cellular metabolism is little affected and the infected cells can grow and divide.

Question 7

How does virus neutralization by antibodies help in immunity to viral infections?

Answer 7

Antibodies help to prevent entry, uncoating, promote phagocytosis and destruction.

Question 8

How does Cell-mediated immunity help in immunity to viral infections?

Answer 8

Infected cells express viral antigens that can be presented to cytotoxic T-cells.

Question 9

How do Interferons help in immunity to viral infections?

Answer 9

Inhibit viral multiplication and may provide temporary and localized protection for nearby cells.
• Host specific, not virus specific.
• Interferons are induced by double-stranded RNA.
• Activates protein synthesis, degrade viral mRNA and promote apoptosis of virally infected cells.
• Responsible for flu-like symptoms seen in viral infections.
• Alpha interferon therapy is used for treating chronic type C hepatitis.

Question 10

How do o Natural Killer Cells help in immunity to viral infections?

Answer 10

• No specificity.
• Can sense drops in MHC class I levels.
• Respond quickly w/ proliferative and cytolytic response.

Question 11

How are viral diseases controlled through prevention?

Answer 11

Vaccines: live attenuated or inactivated.

Question 12

What is the immunity, antibody, cell mediated and reversion to virulence factors associated with live attenuated vaccines?

Answer 12

Immunity: Many years
Antibody: IgG and IgA
Cell Mediated: Good
Reversion to virulence: Rarely

Question 13

What is the immunity, antibody, cell mediated and reversion to virulence factors associated with inactivated vaccines?

Answer 13

Immunity: usually less
Antibody: IgG only
Cell Mediated: Poor
Reversion to virulence: No

Question 14

How are viral diseases controlled through eradication (needs)?

Answer 14

• No animal reservoir.
• Good vaccine.
• Few or no subclinical cases (no latent stages).
• One antigenic type or only a few (no antigenic switching).

Question 15

How do new viral diseases arise?

Answer 15

1. Political/Social/Environmental changes that increase human contact with an infected carrier or vector (HIV).
2. Genetic changes
   • Point mutations (Influenza, HIV)
   • Intramolecular recombination
3. Genetic reassortment (Influenza)

Question 16

What are the treatments for viral diseases?

Answer 16

o Symptomatic.
o Immune serum – best if given early
o Drugs – limited number though.

Question 17

What are the lab methods for diagnosis?

Answer 17

1. Isolation and growth.
   • Tissue culture, embryonated eggs and intact animals.
2. Cytopathic effects in cells.
   • Cell death and lysis: rounding of cells and then lysis.
   • Formation of syncytia (multinucleated giant cells).
   • Formation of inclusion bodies: Negri bodies in Rabies; Cowdry type A bodies in HSV.
   • Proliferation of host cells: cells pile on one another.
3. Electron microscopy
4. Detection of viral components
5. Serology (evaluation of patient’s immune response)
   • Hemagglutination assay: see if virus binds to RBCs.
   • Complement fixation