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Tuesday, March 5, 2013

An Introduction to HIV-Human Immunodeficiency Virus and AIDS-Acquired Immunodeficiency Syndrome

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Today we will learn about the properties, genetics and diseases caused by HIV- Human Immunodeficiency Virus.

Human immunodeficiency virus (HIV) is an RNA virus that causes Acquired Immunodeficiency Syndrome (AIDS). There are two types of HIV virus - HIV 1 and HIV 2 - and they both cause AIDS.

HIV 1 is found worldwide but HIV 2 is found primarily in West-Africa.

    Properties of HIV virus

    1. HIV belongs to the lentivirus subgroup of retrovirus family (which is known for causing infections that develop slowly over a long period of time). It can take from a year to 10-15 years to develop AIDS. 
    2. They are single stranded, RNA, enveloped virus. 
    3. Contains reverse transcriptase enzyme. 
    4. Not oncogenic but cytolytic. 
    5. Incubation period is long: 6 months to 6 years or more. 
    6. It has a bar-shaped (type D) core surrounded by an envelope containing virus specific glycoprotein (gp-120, gp-41). 
    7. The genome of HIV consist of two identical molecules of SS, positive polarity RNA and is said to be diploid. 

    Structure of HIV

    HIV is one of the two important human T-cell lymphotrophic retroviruses (HTLV) that preferentially infects and kills helper (CD4) T lymphocytes, resulting in the loss of cell mediated immunity and a high probability that the patient will develop opportunistic infection and malignancy in the long run. Read more about the pathogenesis of HIV.
    Other cells (macrophage and monocyte) that have CD4 proteins on their surface are also infected by HIV.

    What are the diseases caused by HIV virus?

    1. AIDS (Acquired immunodeficiency syndrome)

    AIDS is considered the most severe manifestation of infection with HIV characterized by severe loss of the body's cellular immunity which greatly lowers the resistance of the body to infection and malignancy.

    2.ARC(AIDS related complex)

    A set of symptoms, such as lymph node enlargement, fever, loss of weight, diarrhea, and minor opportunistic diseases associated with a weakened immune system, which indicates a less severe form of infection by the HIV virus than AIDS itself. Persons with ARC do not have true AIDS, but exhibit abnormal laboratory findings and certain clinical conditions which are attributed to an HIV infection.

    Genetics of the HIV virus

    The HIV genome contains: 

    1. Group specific antigen (gag) gene: which encode internal core protein eg P24, P17. 
    2. Polymerase (pol) gene: encodes several proteins including virion eg Reverse transcriptase which synthesizes DNA by using genome RNA. 
    3. Envelop (env) gene: encodes gp 160 a precursor of glycoprotein that is cleaved to from two enveloped glycoproteins, eg gp 120 and gp 41. 
    The genome also contains 6 regulatory genes:

    • Trans-Activator of Transcription (tat) and Regulator of Virion Expression (rev) genes: These genes are required for replication of HIV virus.
    • Negative Regulatory Factor (nef), Viral infectivity factor (vif),Viral Protein R (vpr) and Viral Protein Unique (vpu) genes: These are called accessory genes as they are not required for replication but they do play a role in evading the immune system.
    HIV Test at PersonaLabs

    That's all for today!
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