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Human immunodeficiency virus

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The human immunodeficiency virus (HIV) is considered to be one of the most devastating infectious diseases to have emerged in the recent history.

  • it is a chronic condition characterized by progressive immunodeficiency, a long clinical latency period and opportunistic infections (1)
  • HIV is the cause of the acquired immune deficiency syndrome (AIDS)

HIV is a member of the lentivirus genus of the Orthoretrovirinae subfamily of the Retroviridae family of viruses (2)

  • various different primates are naturally infected with more than 40 different lentiviruses, termed simian immunodeficiency viruses (SIVs)
    • these viruses are largely nonpathogenic in their natural hosts
  • cross-species transmissions of these SIVs from different primates resulted in the emergence of HIV (3)

HIV targets primarily CD4 positive cells (CD4+) and replicates rapidly within these cells throughout all stages of the infection

  • normally a healthy human has a CD4+ count of 800 to 1200 cells per mm3 of blood
  • HIV causes qualitative defects in function and progressive destruction of CD4 cell count which results in an immunological decline
    • initially replacement of CD4 cells matches the rate of destruction, but in AIDS the gap between destruction and replacement widens and immunological failure occurs
    • usually it takes a number of years for CD4 counts to reduce to levels which will compromise the immune system
      • once the CD4+ count drops below 500 cells/mm3, minor infections including cold sores (herpes simplex), condyloma (warts) and fungal infections, thrush and vaginal candidiasis, may occur
      • as the CD4+ count drops below 200 cells/mm3, patient becomes susceptible to the serious opportunistic infections and cancers characteristic of end stage HIV infection
    • many of the characteristic consequences of AIDS are due to immunological failure (4,5).

An individual is said to have a HIV infection when he /she is recognized with HIV infection regardless of the clinical stage (which includes severe or stage 4 clinical disease also known as AIDS) and confirmed by laboratory criteria according to country definitions and requirements (3).

There are two distinct types of HIV:

  • type 1 (HIV-1) - causes the majority of infections throughout the world
  • type 2 (HIV-2) - seen mostly in West Africa, although individual cases have been reported in other parts of Africa, Europe, the Americas and Asia (India) (6).

Reference:


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