Persistent Viral Infection L22-23

Question 1

List the possible reasons as to why the immune system could fail to clear a virus.
(4)

Answer 1

• Immune deficiency of host
• Virus is poorly immunogenic – induces weak or no immune response
• Virus has evolved “immune evasion” strategies
• Virus suppresses immune response

Question 2

Describe the Hepatitis B Virus genome.

4

Answer 2

• Small genome (3.2kbp) 4mRNAs, 7 proteins
• Multiple promoters
• Overlapping reading frames
• Alternative start codons

Question 3

Describe the functions of the HBV P protein (polymerase).

4

Answer 3

• Completes the partially ds DNA to make full ds DNA genome
• Acts as a reverse transcriptase – copies viral RNA pre-genome into ssDNA
• Has RNAase H activity – degrades the viral RNA pre-genome after copying into DNA
• Synthesises a partial second DNA strand of genome

Question 4

True or false? Outcome of HBV infection depends upon complex interplay between innate, humoral and cell mediated immune responses.

Answer 4

True.

Question 5

How do you prevent contracting HBV?

2

Answer 5

• Avoid body fluid contact – eg. avoid unprotected sex, needle sharing
• Vaccine – recombinant vaccine – recombinant HBSAg produced in Yeast cells

Question 6

How do you treat HBV?

3

Answer 6

• Interferon-a
• Nucleoside analogues
• Liver transplant

Question 7

What type of virus is the HCV virus?

What type of genome code does it contain?

Answer 7

• Flavivirus

- +ve ssRNA genome

Question 8

How is the HCV virus transmitted?

Answer 8

In the blood.

Question 9

True or false? Alpha Herpes viruses establish latent infection in the dendrites of sensory neurones.

Answer 9

False. Alpha Herpes viruses establish latent infection in the nucleus of sensory neurones.

Question 10

Describe the type and size of the HSV-1 genome.

Answer 10

• Large linear ds DNA genome

- 153 kbp

Question 11

How many genes does the HSV-1 genome contain?

Answer 11

~70 genes.