Coupon Accepted Successfully!

Human immunodeficiency viruses

a. Two antigenic types HIV 1 & HIV2
Differences between hiv1 and hiv2
Related to Chimpanzee simian immunodeficiency virus Sooty manageably simian immunodeficiency virus
Geographical distribution World wide West Africa
Virulence More virulent Less virulent
Envelope antigens
Spike antigen
Transmembrane pedicle antigen
gp 41
gp 36
Matrix protein antigen p17 p16
Capsid protein antigen p24 p26
Groups & subtypes Divided into three groups based on even gene sequences
M (major), N (new), O (outlier)
M comprises of 8 subtypes or clades (A,B,C,D,F,H,J, K)
comprises of 9 subtypes
India commonest: C
Western countries: B
5 subtypes (A-F)
b. The genome of HIV contains:
i. Three structural genes:
  • Gag (group-specific antigen): Core protein : p24 and Matrix protein: p17
  • Pol (polymerase): Reverse transcriptase: p51, Protease: p11, Integrase: p32
  • Env (envelope): Outer envelope glycoprotein: gp120 and Transmembrane envelope glycoprotein: gp41
ii. Six non-structural genes:
  • Vif,
  • vpr,
  • vpu (vpx instead of vpu in HIV2),
  • rev,
  • tat  
  • nef odes of transmission:
Route Efficacy
Blood transfusion >90%
Perinatal 13-40%
Sexual intercourse
1% per episode
0.1% per episode
Intravenous drug use 0.5-1%
Needle stick injury 0.3%

c. In India commonest mode of transmission is by heterosexual route

  1. Receptor for HIV: CD4
  2. Co-receptors: CXCR4, present on lymphocytes; CCR5, present on macrophages; coreceptors are require for the fusion of viral envelope with cell membrane.
  3. AIDS is a unique sexually transmitted disease without local genital manifestations at any time during the infection but with grave systemic manifestations.
  4. Infection of resident macrophages and submucosal lymphocytes in the genital tract or rectum→ virus transported to draining lymph nodes→ replication→ after 2-3 weeks viraemia→ fall in CD4+ T cells, glandular like fever→ within one month viraemia declines and illness subsides→ followed by long asymptomatic period, average 10 years→ low titres present in blood, but high level in lymph nodes→ slow destruction of CD4+ T cells→ when count falls below 500/μl, person becomes susceptible to opportunistic infections & cancers→ death due to opportunistic infections & malignancy

Receptor of HIV (AIPG 09)
A. CD 4                          
B. CD 8                    
C. Plasma cell                  
D. CD56


Ans. A

Laboratory diagnosis
i. Screening  (E/R/S) tests:
    Rapid tests: time less than 30 minutes, donot require expensive equipment, but more expensive per test than ELISA, Dot blot assay, Particle agglutination (gelatin, RBC, latex), HIV spot & comb test
    Simple tests: time 1-2 hours, do not require expensive equipment
ii. Supplemental tests:
  • Western blot assay
1. Immunofluorescence test
iii. Confirmatory tests:
  • Virus isolation
  • Detection of p24 antigen
  • Detection of viral nucleic acid: in situ hybridization, PCR
d. Strategies for HIV testing
  1. Strategy I: the serum is tested with one E/R/S test and if reactive, sample is considered positive and if nonreactive it is considered negative. Used for testing blood for transfusion
  2. Strategy II: the serum reactive with one E/R/S test is retested with a second E/R/S test based on different antigen or different test principle. If found reactive on second test it is reported as positive, otherwise negative. Used for HIV surveillance
  3. Strategy III: the serum reactive with two E/R/S tests is retested with third E/R/S. The third test should be of different antigen system of different principle. A serum reactive in all three tests is considered as positive while serum sample nonreactive in third E/R/S test is considered equivocal/ borderline. Such individuals should be retested after three weeks. Used for diagnosis of HIV infection in an individual case
e. Postexposure prophylaxis
i. Exposure code

Exposure to blood, body fluid or instrument contaminated with one of these substances
  • No: no PEP required
  • Yes: Type of exposure
  • Intact skin: no PEP required
  • Mucous membrane/ skin integrity compromised : PEP required
ii. Volume
  • Small/ short duration: EC1
  • Large/ long duration: EC2
iii. Percutaneous exposure
  • Less severe (solid needle/ superficial scratch): EC2
  • More severe (hollow needle/ deep puncture): EC3
iv. Source code
  • HIV negative: no PEP required
  • HIV positive
  • Low titre exposure (asymptomatic/ high CD4 count): SC1
  • High titre exposure (AIDS, primary HIV infection, low CD4 count): SC2
Postexposure prophylaxis
Exposure code Source code Pep regimen
1 1 May not be required
1 2 Basic
2 1 Basic
2 2 Expanded
3 1 or 2 Expanded
f. Prophylaxis
i. Basic regimen
1. Zidovudine 300mg BD or 200mg TDS for 4 weeks
2. Lamivudine 150mg BD for 4 weeks
ii. Expanded regimen
1. Basic regimen + indinavir 800mg TDS for 4 weeks

Test Your Skills Now!
Take a Quiz now
Reviewer Name