The acquired immunodeficiency syndrome (AIDS) was first recognized in 1981 and has since become a major worldwide pandemic [see figures 1, 2, 3, 4]. Abundant evidence indicates that AIDS is caused by the human immunodeficiency virus (HIV) [see figure 5], which was discovered in 1983. By leading to the destruction and/or functional impairment of cells of the immune system, notably CD4+ T cells, HIV progressively destroys the body's ability to fight infections and certain cancers.

Why Is There Overwhelming Scientific Consensus That HIV Causes AIDS?

Before HIV infection became widespread in the human population, AIDS-like syndromes occurred extremely rarely, and almost exclusively in individuals with known causes of immune suppression, such as chemotherapy and underlying cancers of certain types. A marked increase in unusual infections and cancers characteristic of severe immune suppression was first recognized in the early 1980s in homosexual men who had been otherwise healthy and had no recognized cause for immune suppression. An infectious cause of AIDS was suggested by geographic clustering of cases, links among cases by sexual contact, mother-to-infant transmission, and transmission by blood transfusion. Isolation of the HIV from patients with AIDS strongly suggested that this virus was the cause of AIDS. Since the early 1980s, HIV and AIDS have been repeatedly linked in time, place and population group; the appearance of HIV in the blood supply has preceded or coincided with the occurrence of AIDS cases in every country and region where AIDS has been noted. Individuals of all ages from many risk groups -- including men who have sex with men, infants born to HIV-infected mothers, heterosexual women and men, hemophiliacs, recipients of blood and blood products, healthcare workers and others occupationally exposed to HIV-tainted blood, and male and female injection drug users -- have all developed AIDS with only one common denominator: infection with HIV.

HIV destroys CD4+ T cells, which are crucial to the normal function of the human immune system. In fact, depletion of CD4+ T cells in HIV-infected individuals is an extremely powerful predictor of the development of AIDS. Studies of thousands of individuals have revealed that most HIV-infected people carry the virus for years before enough damage is done to the immune system for AIDS to develop; however, with time, a near-perfect correlation has been found between infection with HIV and the subsequent development of AIDS. Recently developed, sensitive tests have shown a strong correlation between the amount of HIV in the blood and the subsequent decline in CD4+ T-cell numbers and development of AIDS. Furthermore, reducing the amount of virus in the body with anti-HIV drugs can slow this immune destruction.

These issues and other evidence that HIV causes AIDS are discussed in more detail in the documents and other resources below.

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