Hepatitis B & Picornaviruses

Question 1

Hepatitis A and Hepatitis B belong to which Baltimore class and what Family?

Answer 1

Hep A: Class 4 (picornaviridae Fam)
Hep B: class 7 (hepadnaviridae fam)

Question 2

Describe the steps involved in Hepatitis B replication after the viral genome has entered the host cell nucleus.

Answer 2

dsDNA: Pos strand DNA shorter than neg strand
1. host DNA pol elongates rest of Pos strand
2. HBV DNA circularises
3. RNA (pgRNA) intermediate act as template = produce cDNA via RVS transcriptase
4. Assempbled in cytoplasm
5. Release by budding
*DNA -> RNA -> DNA

Question 3

What is a pregenome RNA (pgRNA)?

Answer 3

template for HBV DNA synthesis by RVS transcription

Question 4

a) 3x types of particles produced by HBV & which is non&infectious?
b) How are the non infectious particles of Hepatitis B produced?

Answer 4

a) Dane (infect), Spheres & filaments (non)
b) Only surface proteins w/ no DNA or RVS transcriptase (decoy for I.Sys)

Question 5

Name the three antigen types produced by a Hepatitis B infection.

Answer 5

• Surface Ag (HBsAg)
• Core Ag (HBcAg)
• Endogenous Ag (HBeAg)

Question 6

The persistence of which two Hepatitis B antigens indicates chronic infection?

Answer 6

• HBsAg (surface): excess in hepatocytes = ground glass appearance
• HBcAg? (core):

Question 7

Name three diseases caused by Picornoviruses (class4)

Answer 7

• Polio
• Rhinovirus (common cold)
• Foot & mouth disease

Question 8

By what mechanism do Picornaviruses (Class 4) cause disease?

Answer 8

1. pits on capsid bind to receptors
2. Virus endocytosed & low pH => capsomere dissociate = release ssRNA(+)
3. Viral protein synthesis => RNA dependent RNA pol
4. Genome synthesis/replication: ssDNA (+) template = ssRNA(-) => template to make more (+)ssRNA
5. Inc (+)RNA for translation & replication
6. Assembly in cytoplasm
7. cell Lysis

Question 9

How do Picornaviruses stop production of host cell proteins and ensure production of viral proteins?

Answer 9

Cap-independent translation
-N: initiation factors binds cap on mRNA to 40s ribosome then 60s = initiate translation
Infected:
1. viral proteolytic enz destroy initaition factors= cap translation stopped
2. host cell protein bind to Internal ribosome entry site (IRES) -> 40s ribosome bind (to stem loops) => translation
3. 1x polypetide - part of it folds & act as protease

Question 10

If aseptic meningitis is mild and self limiting, why is important to test for the Enteroviruses that cause it?

Answer 10

To ID that meningitis is from a viral infection & not bacterial?
- using RVS transcription PCR for viral RNA: RNA -> DNA -> PCR