Natural history of HIV/AIDS

AIDS is caused by HIV types and 2. HIV affects 40 million people in the world, with 4.9 million new cases and 3.1 million deaths as estimated by the WHO in 2004. Two decades of study into the pandemic have given a wealth of information about the natural history of HIV. With the advent of antiretroviral drugs, prognosis has changed dramatically, with the potential for normal or near-normal life expectancy. HIV infection occurs by transmission of the virus to an uninfected individual by contact with blood or bodily fluids, by sexual contact or through breast milk. Most people seroconvert by 3 months and are HIV antibody positive; 40-90% have a seroconversion illness. This may be associated with an opportunistic infection as the CD4+ count transiently declines below 200/µl. After seroconversion, the CD 4 count usually increases again, but usually to a level below normal. Patients with a CD4+ count of 350-800/µl are invariably well. The length of time it then takes for an individual to develop late-stage disease or AIDS varies. During this period, patients may be completely asymptomatic. Without HIV therapy, eventually the CD4 count declines, and between 200 and 350 the individual becomes increasingly likely to develop non-AIDS-defining infections such as herpes zoster and oropharyngeal candidiasis. Below 200/µl, opportunistic infections and particular HIV-related tumours may develop. Since the introduction of highly active antiretroviral therapy, there has been an 80% decrease in mortality in industrialized nations.