AIDS

Abstract

Acquired immune deficiency syndrome (AIDS) is a severe immune deficiency caused by infection with human immunodeficiency virus (HIV). This is an RNA retrovirus of the subfamily Lentivirnae, members of which typically have a slow progression from infection to overt disease. In addition to a propensity to opportunistic infection, the disease is often also associated with central nervous system degeneration, lymphadenopathy and anaemia. Initially it was thought that the virus had tropism for T cells with the CD4 receptor, mainly helper T lymphocytes, where it replicates and becomes part of the host cell’s genetic material. It is now known that the virus may infect a variety of tissues such as brain, gastrointestinal tract, kidney, lung and possibly heart (Levy 1990). Although the virus core is composed of a single strand of RNA reverse transcriptase, it enables transcribed double-stranded DNA to become permanently imprinted into infected cells. Fully expressed AIDS usually occurs after replication has caused progressive destruction of the body’s cellular immune system. In 1981 the Centres for Disease Control in the USA first drew attention to a new syndrome, predominantly affecting homosexual men, and causing Kaposi sarcoma, Pneumocystis carinii pneumonia and other opportunistic infections (Anonymous 198la, b). Since then, seropositive testing of a specimen taken from a patient in Zaire in 1959 has indicated that the disease had long existed at a low level of prevalence and awareness (Nahmias et al. 1986). Shortly thereafter an additional virus was identified and reported to cause a similar syndrome in West Africa (Clavel et al. 1987). The viruses are now distinguished as types 1 and 2. HIV-2 still has a restricted geographic distribution, but is reported to occur on continents other than Africa.