Infection 11 - HIV

Question 1

Describe the structure of the HIV virus

What cells does it infect?

Answer 1

• (+) sense single stranded RNA retrovirus
• Enveloped
• Infects cells w/CD4+ surface receptor (T-helper cells and monocytes/macrophages)

Question 2

Describe the lifecycle of a HIV particle

Answer 2

• Binds to CD4+ molecule and one of the co-receptors (either CCR5 or CXC4R), virus contents emptied into cell
• Reverse transcription of viral RNA into ds DNA via reverse transcriptase + integration into host DNA via integrase enzyme
• Transcription + assembly of viral protein chains, these bud out the cell and break free.

Question 3

How is HIV transmitted?

Answer 3

• Contact of infected bodily fluids with mucosal membrane or broken skin - through sexual contact, blood transfusion or contaminated needles.
• Perinatal (horizontal) transmission, from mother to foetus during birth

Question 4

Describe the course/process of a HIV infection

Answer 4

• Primary infection, massive replication of virus and small drop in CD4 count.
• Viral load settles to “set-point”, then goes latent, gradually replicating
• CD4 gradually drops. Below 350 cells/uL = infections, below 200 cells/uL = severe AIDS defining infections

Question 5

What are the symptoms of acute HIV infection?

Answer 5

• Fever
• Weight loss
• Malaise
• Headache

Basically similar to a normal cold/flu etc during acute phase.

Question 6

What are the conditions associated with severe HIV (i.e.: >200 cell/uL)

Answer 6

Serious infections including

• Cytomegalovirus (CMV)
• Cryptococcal meningitis
• Reactivation of TB
• Body wasting away
• Opportunistic viruses able to thrive

Question 7

What factors affect HIV transmission?

Answer 7

• Type of exposure - e.g.: type of sexual act
• Viral load - high viral load more likely to infect
• Condom use - large preventative factor
• Breaks in skin/mucosa - increases risk of transmission
• Pro-exposure prophylaxis (PEP) within 72 hours of exposure reduces risk of serious infection

Question 8

What tests are done for diagnosis of HIV?

Answer 8

1) Serology - blood tests for HIV antigen (Ag) or HIV antibody (Ab)
2) PCR - detects viral nucleic acid (expensive)
3) Rapid tests - detects antibody (low cost) - e.g.: saliva or finger-prick blood test. Confirm with serology.

Question 9

How is HIV treated?

Answer 9

• Anti-retroviral drugs

1) CCR5 inhibitors (entry inhibitor)
2) Integrase inhibitors (present incorporation of viral DNA)
3) Reverse transcriptase inhibitors (NNRTI (non-competitive) or NRTI’s (competitive))

HAART = 2 x NRTI’s + NNRTI or protease inhibitor