3 HIV

Question 1

what family does HIV belong to

Answer 1

Retroviridae family

Question 2

how is cDNA replication intermediate made

Answer 2

RNA viruses which use RNA-dependent DNA polymerase (reverse transcriptase) to make a cDNA replication intermediate

Question 3

what are the 4 HIV-1 groups

Answer 3

M
N
O
P

Question 4

what is group M HIV-1

Answer 4

majority

cause of the global HIV-1 epidemic; many strains

Question 5

what is group N HIV-1

Answer 5

non-O/non-M

Question 6

what is group O HIV-1

Answer 6

outlier

Question 7

what does HIV-2 cause

Answer 7

Non-pandemic

Question 8

where is HIV-2 found

Answer 8

largely restricted to West Africa

Question 9

why is HIV-2 restricted to West Africa

Answer 9

HIV-2 may less efficiently transmitted than HIV-1

Question 10

which is most pathogenic

Answer 10

HIV-1

Question 11

effect of HIV-2 infection - symptoms

Answer 11

HIV-2 infected persons seem to remain symptom-free longer than persons infected with HIV-1

Question 12

what may protect against HIV-1

Answer 12

prior HIV-2 infection

Question 13

what does HIV-1 give rise to

Answer 13

HIV-1 gives rise to Group M, which leads to HIV pandemic

HIV-1 gives rise to Group P, O and N

Question 14

gene structure of HIV

Answer 14

Two copies of +sense RNA
Diploid genome – two copies of RNA, genomes can recombine = generate diversity
Surface of lipid membrane have spikes that allow it to attach to membrane
Long terminal repeats on ends

Question 15

what are genes are present in all HIV

Answer 15

All have Gag, Pol and Env gene

Question 16

what additional genes for HIV are there

Answer 16

HIV has additional genes that are involved in replication and that allow it to escape from normal protective mechanisms

Question 17

HIV replication - replication and antiretrovirals

Answer 17

Virus bind to CD4
Virus enters where reverse transcription occurs
DNA made, integrated into host chromosome
- can stay dormant (rare)
or
- immediately start making new viruses – translation
Assembly of virus, viral budding – released from cell

Question 18

how is variability formed

Answer 18

point mutations as reverse transcriptase has no proof reading capability

Question 19

HIV against immune system

Answer 19

immune escape by changing/masking antigenic determinants

- CTLs and Abs

Question 20

what causes resistance to anti-retroviral drugs

Answer 20

• Point mutations in enzymatic proteins

Question 21

effect of point mutations in enzymatic proteins

Answer 21

> RT - resistance to nucleoside and non-nucleoside analogues

> Protease - resistance to protease inhibitors

Question 22

what causes altered cytopathogenicity

Answer 22

Env mutations alter co-receptor usage

Question 23

effect of Env mutations alter co-receptor usage

Answer 23

> Different cell tropism, eg. Macrophages, T-cells,

> Different tissue tropisms, e.g. brain

Question 24

Transmission

Answer 24

Transcutaneous
Sexual
Vertical

Question 25

Transcutaneous transmission

Answer 25

- IVDA - Needle-stick injury - Contaminated blood and blood products

Question 26

sexual transmission

Answer 26

homosexual | heterosexul

Question 27

vertical transmission

Answer 27

(mother-infant) (if child has HIV, will get AIDs very quickly)

Question 28

Clinical Features of HIV Infection (progression)

Answer 28

1. Acute Primary Infection Syndrome 2. Asymptomatic Infection 3. Symptomatic HIV Infection and AIDS

Question 29

Acute Primary Infection Syndrome

Answer 29

Flu-like illness, with high levels of virus replication until the infection is brought under immune control

Question 30

Asymptomatic Infection

Answer 30

No outward sign of disease, although there is a slow decline in the CD4 count, and very active viral replication. This stage can persist for 10+ years

Question 31

Symptomatic HIV Infection and AIDS

Answer 31

The immune system ceases to function and disease progresses, resulting in death

Question 32

Acute Phase HIV-1 antibody type

Answer 32

antibody negative

Question 33

Acute Phase HIV-1 RNA antigen type

Answer 33

antigen positive

Question 34

Acute Phase virus co-receptor

Answer 34

Virus usually uses CCR5 co-receptor

Question 35

effect of HIV on cell count

Answer 35

HIV causes CD4 cell count to become low = 200/ul blood or less = clinical AIDS

Question 36

effect of seroconversion - acute phase

Answer 36

- HIV-1 antibody positive | - Decreased viraemia (RNA , Antigen )

Question 37

Asymptomatic Phase

Answer 37

Active replication within lymph tissue

Question 38

Symptomatic Phase | General dissemination of virus

Answer 38

CNS, other non-lymph tissue

Question 39

Symptomatic Phase | Opportunistic infections/tumours

Answer 39

TB, Kaposis sarcoma

Question 40

what has an Inexorable battle between

Answer 40

the virus and the host

Question 41

viral phenotypes

Answer 41

Transmission and Asymptomatic – virus that exists use CCR5

Question 42

resistance to HIV infection

Answer 42

Homozygote 32/ 32 - CCR5

Question 43

HIV-1-Exposed Seronegative Sex-Workers protection

Answer 43

Protection associated with rare HLA types | - Targeting highly conserved T-cell epitopes

Question 44

how do viruses escape the immune system

Answer 44

Point mutations in key epitopes bound to HLA molecules (which are recognised by cytotoxic T-cells) Some mutations neutral, but some induce fitness cost

Question 45

what causes a large cost to virus to escape immune system

Answer 45

mutating epitopes recognised by the ‘protective’ HLA types results in large fitness cost to virus