Human Immunodeficiency Virus & Lab Diagnosis

Human Immunodeficiency Virus The Virus & The Laboratory Diagnosis Dr. Sudheer Kher Prof & Head, Dept of Microbiology

HIV Genes Three basic genes – gag – encodes matrix, capsid, nucleic acid binding proteins – pol – encodes reverse transcriptase – env - encodes surface glycoproteins, transmembrane proteins

Regulatory genes  tat ( transactivator of transcription)  rev (regulator of expression of viral protein)  nef ( negative expression factor)  vif (virion infectivity factor)  vpr (stimulating promoter of virus)  vpu (HIV-1) & vpx (HIV-2) small viral proteins

promoting maturation and release of progeny virus from cells.

HIV Antigens Major surface/envelope glycoproteins – gp120 – gp41 anchors gp120 to virus

Major capsid proteins – p24 – P18

Other minor surface & structural proteins – p55

Laboratory Diagnosis Test  Serology    

ELISA Latex Agglutination Western Blot Immunofluorescence

Objective Initial Screening Initial Screening Confirmatory test Confirmatory test

 Virion  RNA, RT-PCR  P24 antigen  Isolation of virus

 Lymphocyte  CD4:CD8 T cell ratio

Detection of virus in blood Early marker of infection Test not readily available Correlate of HIV Disease

Laboratory tests for diagnosis of HIV infection Screening tests

Confirmatory tests

ELISA

Western Blot /Virus isolation /Immunofluorescence Detection of viral nucleic acid - In situ hybridization

Rapid tests - Latex agglutination - Dot blot assay

Simple tests - Particle agglutination

- PCR

Detection of p24 antigen

Before you ask for HIV test  Are you asking for the test

because you feel it is mandatory?  Are you asking for the test out of fear?  Have you acquired basic knowledge of HIV/AIDS?  Do you value human rights? Are you aware that your patient too has rights?

 Are you prepared to do

counseling before asking for the test?  Are you prepared to counsel the patient after the test?  Are you prepared to take informed written consent of the patient before sending the sample?  Are you aware that HIV test is no substitute for your precautions?

Strategies for HIV testing in India  Strategy-I  Serum tested by one of

the E/R/S.  If reactive, sample considered positive  If not reactive, sample considered negative  Use – Transfusion safety  Highly sensitive & reliable kits used

Strategies for HIV testing in India  Strategy-II  Serum reactive with

one E/R/S retested with second E/R/S using different Ag/test principle. If reactive, reported positive.  Use – Unlinked anonymous HIV Surveillance

Strategies for HIV testing in India  Strategy –III  Serum reactive with two

E/R/S tests is retested with a third E/R/S.  Or two of the ERS followed by confirmatory test.  Use – Diagnosis of HIV infection

-Non-specific tests for HIV  Blood counts – Leucopenia – Lymphocyte count less than 400/cmm – Thrombocytopenia

 T-cell subset assay – CD4 count below 200/cmm – Normal CD4:CD8 ratio 2:1. Reversed in AIDS to 0.5:1.

 Hypergammaglobulinaem

ia

 Diminished CMI – Candidial, tuberculin tests.

 Lab diagnosis of

opportunistic infections  Malignancies