7. Retrovirus (HIV)

Question 1

Retrovirus:

Answer 1

A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, changing the genome of that cell.

• contains positive stranded RNA
• reverse transcriptase (RNA-dependent DNA polymerase) produces provirus (cDNA)
• provirus integrates into host genome
• transcription of provirus forming viral RNA
• vRNA & proteins assembled in to virus particles, which bud from the cell

Question 2

First retrovirus?

Answer 2

Rous sarcoma virus causing tumour in chickens

Question 3

What distinguishes retrovirus from other microbes?

Answer 3

RNA-dependent DNA polymerase

Question 4

Dentists suffers from needle-stick injury while operating on a HIV-positive patient, now has to undergo PEP. What does he have to take?

Answer 4

He has to take 2NRTIs and 1 integrase inhibitor

NRTI: nucleotide reverse transcriptase inhibitors

Question 5

What is PEP?

Answer 5

Post-exposure prophylaxis. Medicine to prevent HIV after possible exposure

Question 6

HIV is a ——-virus?

Answer 6

Lentivirus.

Lentivirus is a genus of retroviruses that cause chronic and deadly diseases characterized by long incubation periods, in humans and other mammalian species.

Question 7

Gp 120 on HIV binds to which part of T cell?

Answer 7

CD4 receptor

Question 8

Acute HIV symptoms appear after

Answer 8

1-6 weeks/ a month

Question 9

Immune effector cell that keeps HIV down

Answer 9

CD8

Question 10

The Western Blot Test tests for?

Answer 10

HIV antibodies

The Western blot test separates the blood proteins and detects the specific proteins (called HIV antibodies) that indicate an HIV infection.

Question 11

Needle stick HIV transmission risk is

Answer 11

0.4%

Question 12

Standard test for HIV:

Answer 12

1. ELISA test: test for p24
2. Western Blot test: to confirm a positive ELISA/rule out false +ve, test for HIV antibodies, gp120/160 (responsible for marked lines)

Question 13

What is ELISA?

Answer 13

• enzyme-linked immunoassay
• test to detect antibodies in the blood
• most widely used to detect or diagnose virus infections, esp infection of blood borne viruses e.g. HBV, HCV, HIV and HTLV

Question 14

How long does it take for HIV to progress into AIDS?

Answer 14

8-15yrs

Question 15

What is responsible for marked lines on a HIV western blot test?

Answer 15

Antibodies (specifically, gp120/160)

Question 16

How is HIV transmitted?

Answer 16

• by blood, semen & vaginal secretions
• NOT by saliva/casual contact ( cannot exist in cell-free state in saliva)

Question 17

Why cant HIV survive in saliva?

Answer 17

• cannot exist in cell-free state in saliva
• IgA group antibodies in saliva neutralise infectivity of virus => lose infectivity in 30min
• high mucin conc entrap virus
• salivary leukocytes protease inhibitor block all cell surface receptors, needed for HIV entry into cells

Question 18

The highest rate of transmission of HIV occurs due to..

Answer 18

Injecting drug users (highest rate of transmission of HIV)

Other causes of transmission:
1. Vaginal sex
2. Oral sex
3. Needle stick injury