Session 6 ILOs - Blood borne viruses (HIV and Viral Hepatitis)

Question 1

Describe the principles of HIV structure and replication (including the 4 stages of infection)

Answer 1

Human Immunodeficiency virus:

Structure/details:

• Retrovirus
• It infects cells with CD4 surface receptors (T-helper lymphocytes and monocytes/macrophages)
• Has surface antigens (gp120 and gp41), has 3 key enzymes (integrase, reverse transcriptase) protease) and a viral RNA genonme within a nuclear envelope

Replication:

1. Free virus in the blood binds to CD4 receptors (using CCR5 or CXCR4 coreceptors)
2. Virus penetrates the cell and empties it’s contents
3. ssRNA are converted into dsDNA by reverse transcriptase enzyme
4. Viral DNA is integrated into the host’s DNA by integrate enzyme
5. When the cell divides, the viral DNA is read and long chains of proteins are made and viral protein chains come together
6. Immature virus pushes out of the cell, taking some of the cell membrane with it and the immature virus breaks free of the cell
7. Protein chains are cut by the protease enzyme into individual proteins that combine to make a working virus

4 stages of infection:

1. Primary infection / seroconversion
2. Latent infection
3. Symptomatic infection
4. Severe infection / AIDS

Question 2

Describe the principles of transmission and prevention with regard to HIV

Answer 2

Transmission:
- Occurs through contact of infected bodily fluids with mucosal tissue, blood or broken skin
Examples:
- Sexual contact (most common)
- Transfusion (rare in UK)
- Contaminated needles
- Perinatal transmission (during birth or childbirth)
= affected by type of exposure, viral level, condom use and breaks in skin or mucosa

Prevention:

• Increase condom usage
• ARV treatment use as prevention
• Wide-spread testing/screening
• Prevention of mother to child transmission
• Pre-exposure prophylaxis
• Post-exposure prophylaxis

Question 3

Describe the principles of Hepatitis replication

Answer 3

Hepatitis = inflammation of the liver

Hepatitis infection works in a similar way to HIV in hijacking the hepatocytes specifically and integrating into the genome.

Question 4

Describe the principles of infection transmission and prevention with regard to Hepatitis B

Answer 4

Transmission:

• Vertical transmission (75% of cases WW)
• Sexual contact
• IV drug users
• Close household contacts
• Health care workers and needle stick injuries

Prevention:
- Mainly through vaccination (esp. of health care workers (NO CURE)

Question 5

Describe the principles of HIV testing and treatment

Answer 5

Blood test (serology) = test anyone with unusual symptoms or if a high rate of HIV in community

1. Antibody/Antigen test (main test) - +ve 4 weeks after the infection
   - Detects antibodies against HIV
   - Detects HIV itself
2. PCR test - used for follow up/treatment response
   - Detects HIV nucleic acid
   - Highly sensitive but very expensive with slow results (so not used for initial HIV testing)
3. ‘Rapid tests’ for HIV antibody
   - Detects antibodies against HIV
   - Can be blood test or saliva (home testing or postal kits)
   - May get a false positive result (need to confirm with serology)

Treatments (ARV drugs - target enzymes in replication) = start ASAP:
- Give 2 reverse transcriptase inhibitors and 1 other drug option e.g. protease inhibitor

Question 6

Describe the principles of Hepatitis B testing and treatment

Answer 6

Testing (serology):
- Surface antigen first (1-5 months roughly)
- Then e-antigen (2-4 months)
- Then core antibody IgM (after 3 months)
- Then e-antibody (after 5 months)
- Then surface antibody (after 6 months)
- Then core antibody (IgG form)
Chronic Hep B infection = persistence of surface antigen after 6 months

Treatment:

• NO CURE
• If caught, need to be on lifelong antivirals to suppress viral replication (but not required for everyone if they have a low viral load)

Question 7

Describe the principles of transmission and prevention with regard to Hepatitis C

Answer 7

Transmission:

• IV drug users most at risk (>90% of cases)
• Sexual contact (<1%)
• Infants born to Hep C positive mothers

Prevention:

• NO VACCINE
• Just need to avoid high risk transmission situations

Question 8

Describe the principles of Hepatitis C testing and treatment

Answer 8

Testing:

• More simple than Hep B testing!
• Only looking for anti-Hep C antibody
• Remains positive life-long even after clearance/cure
• But not protective, can still get reinfected

Treatment:

• Can be cured!
• Directly acting antiviral drug combination for 8-12 weeks (>90% chance of cure) - but it’s very expensive!!