What is HIV?In 1981 an epidemic of a previously unknown acquired immune deficiency syndrome (AIDS) was described in the USA. A lentivirus (subfamily of retroviruses) was subsequently identified. Lentus (in Latin = slow) denotes the long latent phase between infection and the development of symptoms. Retroviruses use the enzyme reverse transcriptase (RT) to generate proviral DNA from RNA (reverse of the usual direction of genetic transcription). The term human immunodeficiency virus (HIV) was accepted in 1986. In the same year a related virus (HIV-2), endemic in W. Africa, and sharing common features including the induction of immune deficiency, was identified.
Origin of HIVThere are structural and genomic organizational similarities between HIV and simian immune deficiency virus (SIV). Despite similarity between HIV-1 and 2, there is little sequence homology with HIV-2 more closely related to SIV than to HIV-1. Phylogenetically, HIV-1 and HIV-2 cluster with chimpanzee (Pan Troglodytes) and sooty mangabey simian retroviruses, respectively. SIVcpz is almost identical to HIV-1. It appears likely that the virus at some point crossed species from chimpanzees to man.
Evidence that the virus existed for some time before its effects became clinically apparent in 1981 is supported by the following:
Prevalence of HIV38 million people, 2.1 million of them children, were living with HIV/AIDS by the end of 2003 (two-thirds in sub-Saharan Africa). An estimated 4.8 million new infections occurred in 2003.
The number of people living with HIV is ↑ because of the continuing epidemic and the availability of life prolonging drugs. Infection rates are likely to ↑ in countries with poverty, inadequate healthcare, and limited resources for prevention. The socio-economic impact is greater in developing countries.
HIV Viruses and Their Epidemiology
HIV-1 and HIV-2Differ in several aspects:
HIV-2Divided into group (rather than subtype) A to G.
|HIV : History of HIV : HIV Symptoms : How Do you Get HIV : How to Prevent HIV : HIV Treatment : Types of HIV : HIV Infection : HIV AIDS : HIV Facts : HIV Myths : HIV Life Cycle : HIV Prevention : HIV Rash : HIV Statistics HIV Test : HIV Virus : HIV Helplines|