256442 hiv

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Detecting Recent Human Immunodeficiency Virus Type 1

infection

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Review

HUMAN IMMUNODEFICIENCY VIRUS• Retrovirus• Lead to acquired immunodeficiency syndrome

PREVIOUS NAMES

• Lymphadenopathy- associated virus (LAV)

• Human T Lymphocyte Virus Type III (HTLV III)

• Human Immunodeficiency Virus (HIV)

• AIDS –Associated Virus (ARV)

TWO SPECIES

• HIV- TYPE I- more virulent

- easily transmitted

- cause of majority of

- infections globally

• HIV- TYPE II- less transmittable

- largely confined to West Africa

THREE MAJOR ROUTES

• Unprotected sexual intercourse• Blood or blood products• Mother- to- child transmission

Mechanism of entry to the cell

MORPHOLOGY OF VIRUS

Morphology of HIV

• Viral diameter 120 nm• Roughly spherical• 2 copies of positive single stranded RNA

• Viral envelope composed of 2 layers of phospholipid

• Envelope consists of cap made up 3 molecules called glycoprotein 120

• Stem composed of three glycoprotein 41

HIV- I RNA OR p24 antigen test

P24 antigen

• Sandwich ELISA

DETECTING RECENT HUMAN IMMUNODEFICIENCY VIRUS

TYPE I INFECTION

• Seroconversion – antibody production following exposure to an antigen

• Current serologic window period – 3 to 4 weeks – HIV infection cannot be demonstrated using antibody tests

• p24 antigen test – about 1 week

ELISA plate

Less sensitive enzyme immunoassays

• Less-sensitive (LS) HIV enzyme immunoassays (EIAs) can distinguish persons who have recent HIV infections from those who have long-standing HIV infection.

• Used to test prevalent HIV-positive people and to detect recent seroconversion (within 130 days).

• In most cases the EIA (enzyme immunoassay), used on blood drawn from a vein, is the most common screening test used to look for antibodies to HIV. A positive (reactive) EIA must be used with a follow-up (confirmatory) test such as the Western blot to make a positive diagnosis. There are EIA tests that use other body fluids to look for antibodies to HIV. These include:

• Oral Fluid Tests – use oral fluid (not saliva) that is collected from the mouth using a special collection device. This is an EIA antibody test similar to the standard blood EIA test. A follow-up confirmatory Western blot uses the same oral fluid sample.

• Urine Tests – use urine instead of blood. The sensitivity and specificity (accuracy) are somewhat less than that of the blood and oral fluid tests. This is also an EIA antibody test similar to blood EIA tests and requires a follow-up confirmatory Western blot using the same urine sample.

• When used as a second step in an algorithm to test known positives, it can help identify recent infections, the approach known as serologic testing algorithm for recent HIV seroconversion or STARHS.

• This method measures antibody levels quantitatively; hence their performance in divergent subtypes depends on the extent of cross-reactivity.

Maturation of Humoral Response

• Antigen or epitope specific response

• Antibody Titer• Antibody Affinity• Proportion of HIV-IgG• Antibody Isotypes

IgG- capture EIA

• Uses microwells coated with goat antihuman IgG which captures both HIV and non-HIV – IgG from the serum.

• Increasing levels of HIV-specific antibodies can be detected by this assay from up to two years following seroconversion.

Incidence calculation

• From test results of cross sectional cohort translated to rate of new infections occuring per year taking into account the numbers of individuals at risk.

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