Immunodeficiency virus or HIV is a retrovirus that causes acquired immune deficiency syndrome (Aids), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections.

Immunodeficiency virus or HIV is a retrovirus that causes acquired immune deficiency syndrome (Aids), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections.

Previous names for the virus include Human T-Lymphotropic Virus-III (HTLV-III) and lymphadenopathy-associated virus.

Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, Cowper's fluid or breast milk. Within these body fluids HIV is present as both free virus particles and virus within infected immune cells.

The three major routes of transmission are unprotected sexual intercourse, contaminated needles and transmission from an infected mother to her baby at birth or through breast milk.

Screening of blood products for HIV in the developed world has largely eliminated transmission through blood transfusions or infected blood products in these countries.

HIV infection in humans is now pandemic. As of January 2006, the Joint UN Programme on HIV-Aids (UNAids) and the World Health Organisation estimate that Aids has killed more than 25million people since it was first recognised on December 1 1981, making it one of the most destructive pandemics in recorded history.

In 2005 alone, Aids claimed an estimated 2,4million lives, of which more than 570000 were children.

A third of these deaths occurred in sub-Saharan Africa, retarding economic growth and increasing poverty. - Wikipedia