HIV and AIDS

Question 1

HIV Virology
- Type
- Family
- Genus
- Species and epidemiology

Answer 1

RNA virus
Retroviridae family
Lentivirus genus
HIV-1 (globally); HIV-2 (West Africa)
- It is thought that HIV-2 has lower virulence and infectivity thus confined

Question 2

Replication cycle of HIV

Answer 2

1. Targets CD4+ T cells, macrophages and dentritic cells
   - GP-120 envelope glycoprotein binds to CD4 receptor on target cell membrane
   - Viral caspid enter cell via endocytosis
2. Viral RNA with reverse transcriptase converts RNA into viral DNA, transported into cell nucleus
   - Integrase enzyme integrates DNA into host cell genome
3. Dormant or active transcription of new RNA
   - Virions buds out of membrane and released from cell to spread to other parts
4. Dissemination
   - Bloodsteam
   - Extracellular fluid
   - Local cell-cell spread

Question 3

Course and immune response to HIV infection

Answer 3

1. Initial infection - rapid replication and high viral load
   - High susceptible CD4+ T cells
   - No virus specific immune response
   > Risk of transmission highest during first few weeks (peak viral load)
2. CD8+ cytotoxic T cells response
   - Fall in viral load
   - Specific antibodies against HIV generated (not significant in control)
3. Steady state viral load (viral set point)
   - Within 6 months, correlates with degree of virus-specific CD8+ T cells

Question 4

Mode of transmission of HIV
Risk factors for transmission

Answer 4

1. Sexual transmission > 80%
   - Especially MSM (19 times more)
2. Parenteral transmission
   - IV drug use
   - Contaminated blood transfusion
3. Vertical transmission
   - Mother to child via in utero, at birth or breastfeeding

Risk factors for transmission
1. High viral load
2. Concomitant STI (genital ulcers)
3. High sexual partners count
4. Lack of protection
5. Types of penetration
6. Male circumcision (reduces risks)

Question 5

What are the highest risk exposure route of HIV?

Answer 5

1. Blood transfusion - 90 per 100
2. Mother-to-child - 30 per 100
3. Breastfeeding - 15 per 100
4. Needle sharing - 0.67 per 100
5. Receptive anal intercourse - 0.5 per 100

Percutaneous needlestick 0.3
Receptive penile-vaginal 0.1
Insertive 0.065 and below
Oral sex insertive 0.005, receptive 0.01