Human Immunodeficiency Virus & Lab Diagnosis

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    Human Immunodeficiency Virus

    The Virus & The Laboratory Diagnosis

    Dr. Sudheer Kher

    Prof & Head, Dept ofMicrobiology

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    HIV Genes

    Three basic genes

    gag encodes matrix, capsid, nucleic acid

    binding proteins

    pol encodes reverse transcriptase

    env - encodes surface glycoproteins,

    transmembrane proteins

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    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 proteinspromoting maturation and release of progeny

    virus from cells.

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    HIV Antigens

    Major surface/envelope glycoproteinsgp120

    gp41 anchors gp120 to virusMajor capsid proteins

    p24

    P18Other minor surface & structural proteins

    p55

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    Laboratory Diagnosis

    Test

    Serology ELISA

    Latex Agglutination

    Western Blot

    Immunofluorescence

    Virion

    RNA, RT-PCR P24 antigen

    Isolation of virus

    Lymphocyte CD4:CD8 T cell ratio

    Objective

    Initial Screening

    Initial Screening

    Confirmatory test

    Confirmatory test

    Detection of virus in bloodEarly marker of infection

    Test not readily available

    Correlate of HIV Disease

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    Laboratory tests for diagnosis of

    HIV infection

    Simple tests- Particle agglutination

    Rapid tests

    - Latex agglutination- Dot blot assay

    Western Blot

    /Virus isolation

    /Immunofluorescence

    Detection of viral nucleic

    acid- In situ hybridization- PCR

    Detection of p24 antigen

    ELISA

    Confirmatory testsScreening tests

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    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 docounseling before askingfor the test?

    Are you prepared tocounsel the patient afterthe test?

    Are you prepared to takeinformed written consentof the patient beforesending the sample?

    Are you aware that HIVtest is no substitute for

    your precautions?

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    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

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    Strategy-II

    Serum reactive withone E/R/S retestedwith second E/R/Susing different Ag/test

    principle. If reactive,reported positive.

    Use Unlinkedanonymous HIVSurveillance

    Strategies for HIV testing in

    India

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    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

    Strategies for HIV testing in

    India

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    -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 ratio2:1. Reversed in AIDS to0.5:1.

    Hypergammaglobulinaemia

    Diminished CMI Candidial, tuberculin tests.

    Lab diagnosis of

    opportunistic infections

    Malignancies