Viral Pathogenesis

Question 1

What is Tissue Tropism and what helps to determine it?

Answer 1

Likeliness of a virus to infect tissues and not others; aka tissue specificity.

It is determined by factors such as accessibility, presence of receptors, expression of host genes for viral infectivity, and reduced host defenses.

Question 2

What is virulence? What are the 4 virulence factors/genes?

Answer 2

Virulence is the ability of a virus to cause a disease.

1. Ability to replicate in a host (are toxic to host cells)
2. Ability to “evade” immune detection
3. Ability to “suppress” immune system
4. Ability to spread in and between hosts

Question 3

Within the realm of virulence, what are the types of shedding?

Answer 3

Shedding: Release of infectious particles from infected host.

• Local shedding occurs at sight of infection.
• Disseminated is distant sights.

Question 4

Which type(s) of viruses are transmitted via close contact? Why?

Answer 4

Enveloped viruses- they are more fragile and sensitive to their environment.

Question 5

Which type(s) of viruses are transmitted via respiratory or oral-fecal routes? Why?

Answer 5

Non-enveloped: They can withstand environmental stress better.

Question 6

Viral diseases can be mediated by host immune responses. What are the 4 types of host mediated responses?

Answer 6

1. Antibody Mediated
2. Cell Mediated
3. Autoimmunity
4. Immune suppression.

Question 7

When comparing Acute Systemic Disease and Acute Local Disease, which one has a longer incubation period?

Answer 7

Systemic

Question 8

When comparing Acute Systemic Disease and Acute Local Disease, which one has short lived immunity? Why?

Answer 8

Local. Many serotypes are rapidly mutating.

Question 9

When comparing Acute Systemic Disease and Acute Local Disease, which has a primary infection site of the epithelium?

Answer 9

Both

Question 10

When comparing Acute Systemic Disease and Acute Local Disease, which has a secondary infection site?

Answer 10

Systemic (think, if its local, its not gonna spread)

Question 11

When comparing Acute Systemic Disease and Acute Local Disease, which one has an IgG response?

Answer 11

Systemic.

both have IgA in the mucosa but only Systemic gets IgG

Question 12

When comparing Acute Systemic Disease and Acute Local Disease, which has a higher likelihood of reinfection?

Answer 12

Acute Local Disease

Question 13

Describe the expected outcome of viral infection and disease in a healthy host versus an immune compromised host, including symptoms, shedding and transmission, and length of primary infection.

Answer 13

Best way to do this is with an example.

Consider a rhinovirus:
Healthy host-infection will cause an appropriate immune response (symptoms remain in URI, i.e. irritation in throat, mouth, coughing), and will resolve with time.

Compromised host: infection will result in hyper inflammation of the lungs. Resolution may not occur. Instead, infection can spread to lower part of respiratory tract and cause chronic lung injury.

Question 14

What are two differences between Persistent and Latent infections?

Answer 14

Persistent:

• produces virus and disease for long periods of time
• present in healthy host
• Continuous inflammation and possible tumorigenesis.

Latent

• Virus not produced, but silent in host
• Retains ability to reinitiate transcription at any time.

Question 15

Give an example of an Acute Local and Systematic viral disease and the potential outcome(s).

Answer 15

Local: Colds, diarrhea.
Systematic: Smallpox, Measles

They are infectious and symptomatic for a short amount of time.

Question 16

Give an example of a persistent viral disease and the potential outcome(s).

Answer 16

Hepatitis B+C

Can be asymptomatic, and if persistent long enough, can lead to death.

Question 17

Give an example of a latent viral disease and the potential outcome(s).

Answer 17

Herpes Simplex

Latent, reactivating infections can sometimes be asymptomatic, and at the same time transmit the disease without even knowing it