HIV - (Human Immunodeficiency Virus)

(HIV) - Human Immunodeficiency Virus belongs to the subfamily of retroviruses which have an RNA genome. HIV has a core consisting of the RNA genome and core protein surrounded by an envelope with high lipid content, rendering it sensitive to organic solvents. HIV gains entry to host cell by binding to the CD4 receptor using the viral surface membrane glycoprotein gp 120. Host target cells of preference, therefore,carry the CD4 molecule which is recognized by the virus, but in addition other cell surface molecules act as receptors and co-receptors for the virus. The RNA viral genome is transcribed to DNA copy by reverse transcriptase enzyme.Then the DNA copy integrates into host cell genome in cell nucleus via integrase enzyme. Following cell activation viral DNA is translated to RNA copies in cytoplasm. Viral peptide chains are translated from cytoplasmic viral RNA. HIV proteinase cleaves functional viral proteins from polypeptides. Virion assembly occurs.Viral release from cell surface by cell lysis.
There is a huge diversity amongst HIVs, which occurs in 2 main types: HIV 1 and HIV 2. Disease caused by HIV 2 is similar to disease caused by HIV 1 but is generally milder, slower to progress and poorly transmitted vertically. HIV 1 is responsible for most of the disease seen world-wide.HIV 1 is divided into several subtypes,and there are atleast five subtypes of HIV 2.
The acquired immune deficiency syndrome (AIDS), caused by the HIV-1 RNA retro virus, is the most common acquired immune deficiency in the United States. AIDS is currently the most common cause of death in black men and women from 25 to 44 years of age.
The acute phase of HIV infection develops within 2- 4 weeks of contracting the virus. It is characterized by fatigue, sore throat and lymphadenopathy, the CD4 counts are normal to low, with an increase in the P24 antigen which is an indicator of disease activity. In approximately 4 -12 weeks (window period) antibodies against gp 120 and other antibodies are not detected. ELISA test which are positive are confirmed by western blot analysis, which detects more than one HIV antibody (eg; p24 and gp41). After the acute phase, patient enters an asymptomatic latent phase, in which the actively proliferating virus is present within the dendritic cells located in the lymph nodes.After an average span of 4- 10 years, patients enter the late phase of the disease, where the CD4 count drops below 400 cells/microlitre, the p24 antigen resurfaces, and opportunistic infection develops. AIDS is a multisystem disorder with the lungs representing the most frequently involved site.
An opportunistic infection or a CD4 count of less than 200 cells/microlitre is sufficient to diagnose AIDS. The average life span from the beginning of infection to death of the patient is 10 years.
HIV infection is confirmed by demonstrating the presence of antibodies to HIV in serum.The enzyme -linked immunosorbent assay (ELISA) test used for detecting antibodies to HIV is simple and cheap and has the advantage of a very low false negative rate so that the infected cases are unlikely to be missed. All the positive results are normally confirmed by the more precise western blot test, which also detects the presence of anti- HIV antibodies.Serial testing may be required following a high risk of exposure to HIV to exclude infection. Following HIV infection the production of detectable antibodies to various components of the virus,including antibody to the gag protein, integrase and reverse transcriptase may not occur for 6-12 weeks and sometimes much longer. Antibody detection test are unhelpful and misleading in neonates who may be infected because of the presence of transplacentally acquired maternal antibody. The polymerase chain reaction (PCR) can be used in this situation to detect the presence of viral genome in the peripheral blood lymphocytes.However, ELISA remains the routine screening test and is used by centers offering same day or rapid testing services.The advantage of knowing that an individual is HIV-seropositive include appropriate medical care and prophylactic measures which will benefit health, prolong life, and avoid infection to others. When an HIV test is negative the patient should be advised to practice safe sex and to abstain from avoidable risk factors, such as sharing needles for intravenous drug use.
There are three possible modes of transmission of HIV; sexual, perinatal, parenteral. Infection with HIV essentially requires exchange of semen, vaginal or other body secretions, milk or blood or blood products infected by virus. The risk of HIV transmission is greatest with vaginal and anal intercourse. The risk of transmission during intercourse is further increased by presence of sexually transmitted disease, such as any genital ulceration.
Perinatal transmission is increasing globally as a direct result of the increase in number of women with HIV infection who are of child bearing age. HIV during parturition on contact with HIV-containing fluids in the vagina accounts for around 80% of vertical transmission. Neonates of HIV infected women have a 13-52% chance of acquiring HIV from the mother. In utero the virus may infect the fetus by crossing the placenta. Intravenous drug users (IVDUs) are at risk of HIV infection as a result of sharing needles, which allows transmission of HIV infected blood from one individual to another. Transmission of HIV among health-care workers following occupational exposure is a rare event, the major risk factor is a needle stick injury with HIV contaminated blood from an infected patient.
PREVENTION MEASURES FOR HIV TRANSMISSION:
SEXUAL - public awareness campaigns for HIV, safe sex practice like avoidance of penetrative intercourse and use of condoms, targeting safe sex methods at sex industry workers, and control of sexually transmitted diseases.
PARENTERAL- Routine screening of blood or blood products for HIV, needle exchange programmes of Intravenous drug users (IVDUs).
PERINATAL - Routine HIV testing at antenatal clinics, avoidance of pregnancy if HIV- seropositive, Anti-retro viral therapy during pregnancy, delivery or postnatally.