Infection - HIV

Question 1

Which is more common in the UK - HIV, Hep B or Hep C?

Answer 1

Hep C (1 in 200 people), then HIV (roughly 100,000 people), then hep B (1 in 1000 people)

Question 2

Why is HIV called a ‘retrovirus’?

Answer 2

It travels ‘backwards’ from ssRNA to DNA to ssRNA

Question 3

How does HIV cause symptoms?

Answer 3

It replicates inside body cells, destroying the cell and causing inflammation. It then spreads to/infects more cells

Question 4

How does HIV replicate inside the cell?

Answer 4

• virus binds to CD4 molecule and a co-receptor, then fuses with cell
• contents of virus are emptied into the cell
• ssRNA from virus converted into DNA by reverse transcriptase
• viral DNA combined with cell’s DNA by integrase, so when when infected cell divides, viral proteins are made too
• viral chains come together and immature virus breaks free of the infected cell
• protein chains in new viral particle are cut by protease into individual proteins to make a working virus

Question 5

How is HIV transmitted?

Answer 5

Contact of infected bodily fluids with mucosal tissue/blood/broken skin. Can be through sexual contact, transfusion, contaminated needles or perinatal transmission

Question 6

Why is there an initial drop in CD4 cell count after HIV infection which then recovers?

Answer 6

The viral load increases dramatically after infection, but the immune system then kicks in and begins to decrease the viral load and CD4 count recovers

Question 7

What happens when the CD4 count of a HIV-sufferer drops below 200?

Answer 7

They develop AIDS and have severe symptoms

Question 8

What are the factors that affect how easy it is to transmit HIV between people?

Answer 8

• type of exposure (type of sexual act, transfusion/needle stick/mucous membrane)
• viral load in blood
• condom use
• breaks in skin/mucosa

Question 9

What is the difference in life expectancy between that of the general population and someone with HIV?

Answer 9

As long as they have early detection, adhere to treatment and live healthily (no smoking, alcohol or metabolic problems) then they should have same life expectancy (77 years)

Question 10

How is serology used to detect HIV?

Answer 10

• shows HIV antigen (Ag) which indicates whether viral protein is present
• shows HIV antibody (Ab) which indicates immune response to antigen
• result can be given on same day

Question 11

How can PCR be used to diagnose HIV?

Answer 11

• detects HIV nucleic acid
• very highly sensitive, detects early infection
• disadvantages: expensive, results slow
• used more to test the follow-up response to treatment rather than initial test

Question 12

What are the aims of HIV treatment?

Answer 12

• to have an undetectable HIV viral load
• reconstitute CD4 count
• reduce general inflammation
• reduce transmission risk
• good quality of life
• normalise lifespan

Question 13

How are people with HIV treated?

Answer 13

They are given two nucleoside reverse transcriptase inhibitors, and a non-nucleoside reverse transcriptase inhibitor/ protease inhibitor/ integrase inhibitor = 3 in total

Question 14

Why do we give three anti-retrovirals?

Answer 14

There are millions of rounds of viral replication every day and the virus mutates every 2-3 rounds, so resistance to drugs can develop in days. This is harder with 3 drugs

Question 15

How can HIV spread be prevented?

Answer 15

• increase condom usage
• prevent mother-child transmission
• ARV treatment as prevention
• medical circumcision
• post-exposure prophylaxis
• pre-exposure prophylaxis