Infection 4: How do viruses cause disease?

Question 1

What is meant by neurotropic?

Answer 1

virus can infect neural cells

Question 2

What is meant by neuroinvasive?

Give an example of a very neuroinvasive disease

Answer 2

virus can enter CNS following infection of a peripheral site

E.g Mumps, Rabies

Question 3

What is meant neurovirulent?

Give an example of a very neurovirulent virus

Answer 3

virus can cause disease of nervous tissue

E.g HSV, Rabies

Question 4

What are the 3 main mechanisms for how viruses injure cells?

Answer 4

1. Cytolytic viruses​

Inhibition of host protein and RNA synthesis – leads to loss of membrane integrity​

Syncytium formation​

Induction of apoptosis​

2. Non-cytolytic viruses​

CD8+ mediated ​

CD4+ mediated​

B cell mediated​

3. Cell injury associated with free radicals

Question 5

What is the mechanism by which EBV evades the immune system?

Answer 5

Production of immunosuppressive cytokine

- IL10

Question 6

How does influenza viruses evade host defence mechanisms?

Answer 6

• The virus can change its surface antigens - the immune response no longer able to identify them
• Mechanisms of antigenic variation in HA (hemagluttin) and NA (neuraminidase)
  Antigenic drift
  Antigenic shift

Question 7

What is antigenic drift?

Answer 7

• due to mutations.
  minor change in amino acid composition in hemagglutinin or neuramindase.
• results in decreased ability of the host cells to recognize them.
  occurs among influenza A virus resulting in emergence of new variations of prevailing strains every year.
  EPIDEMICS localized outbreaks

Question 8

What is antigenic shift?

Answer 8

minor change occurs in H or N, usually H.
sub of 1 viral gene or strand w/in a gene or strand of flu virus from another host causes antigenic shift.
When bird + human virus infect pig host, viruses can infect single host cell.
During assembly, RNA strands of the bird and human origin can mix.

PANDEMICS worldwide
outbreak