AIDS

    in full Acquired Immunodeficiency Syndrome , fatal transmissible disorder of the immune system that is caused by the human immunodeficiency virus (HIV). In most cases HIV slowly attacks and destroys the immune system, the body's defence against disease, leaving the infected individual vulnerable to malignancies and infections that eventually cause death. AIDS is the last stage of HIV infection.

Although researchers discovered HIV in a stored plasma sample dating to 1959, the first full-blown cases of AIDS were diagnosed in Los Angeles, California in 1981. Initially most cases of AIDS in the United States were diagnosed in homosexual men, who contracted the virus primarily through sexual contact, and intravenous drug users, who became infected mainly by sharing contaminated hypodermic needles. The agent responsible for the disease, HIV, was isolated in 1983, and by 1985 sero-logic tests to detect the virus had been developed. HIV is contracted mainly through exposure to blood, semen and other genital secretions, and breast milk. Although it is a transmissible virus, it is not contagious and it cannot be spread through coughing, sneezing, or casual physical contact. The major mode of transmission worldwide, that accounts for 70 per cent of all HIV infections, is heterosexual intercourse. The virus also can be spread from mother to child during childbirth or through breast milk. Many individuals, including a number of haemophiliacs, were infected from contaminated blood and blood products before screening procedures were introduced in the late 1980s.

An estimated 38.6 million people world-wide were living with HIV at the end of 2005. An estimated 4.1 million became newly infected with HIV and an estimated 2.8 million succumbed to AIDS. Overall, the HIV incidence rate (the proportion of people who have become infected with HIV) is believed to have peaked in the late 1990s and to have stabilized Subsequently, notwithstanding increasing incidence in several countries.

The United Nations estimates that 5.7 million Indians were infected at the end of 2005, compared with an estimated 5.5 million South Africans. The reason for such a high estimate of HIV-infected individuals in India is relatively low condom use, an uneven public health system, and a large population of floating and migrant workers-a natural client base for prostitution.  

The course of HIV infection usually involves a number of stages. An average interval of 10 years exists between infection with HIV and development of the conditions typical of AIDS. Within the first few weeks of infection, persons often develop an acute mononucleosis-like illness that usually resolves within two to three weeks. During this time a variety of symptoms may occur; they include general malaise, nausea, joint and muscle soreness, fever, rash, sore throat, diarrhoea, stiffness, swollen lymph glands, dementia, and unexplained weight loss. After this stage the infected individual may remain without symptoms for years. As the immune system deteriorates, however, the infected individual becomes susceptible to a variety of diseases. These include infections caused by organisms that do not ordinarily cause disease because they are easily combated by a healthy immune system. In addition, HIV-infected individuals have an unusually high incidence of certain cancers, such as Kaposi's sarcoma, tongue and rectal cancers, and non-Hodgkins B cell lymphoma. The development of one or more of these conditions usually marks the onset of AIDS. Pneumonia is a common disease seen in AIDS patients. Many individuals suffering from AIDS develop a wasting syndrome and become emaciated. Death ultimately results from the relentless attack of diseases or from the body's inability to fight off malignancies.

A small proportion of individuals infected with HIV have survived longer than 10 years without developing AIDS. Many of these -survivors show no signs that the disease is progressing. It may be that such individuals mount a more vigorous immune response to the virus or that they are infected with a weakened strain of the virus.

Two predominant strains of the virus, HIV-1 and HIV-2, are known. The two strains act in a similar manner, but HIV-2 causes a form of AIDS that progresses much more slowly than that caused by HIV-1. No vaccine or cure has yet been developed that can prevent HIV infection. Efforts at prevention have been focussed primarily on changes in sexual behaviour such as abstinence, monogamy, the use of barrier contraceptives, and other "safe sex" methods. Attempts to reduce intravenous drug use and to discourage the sharing of hypodermic needles have also led to a reduction in infection rates in some areas. Therapy was initially limited to treatment of the individual infections as they arose. However, several drugs are now used to slow the development of AIDS once an individual has become infected with HIV.  

At a historic special session of the United Nations General Assembly in 2001, leaders from 189 member states charted the Declaration of Commitment on HIV/AIDS, committing themselves to comprehensive, time-bound targets for the delivery of the effective HIV prevention, treatment, care, and support needed to halt and reverse the global epidemic by 2015.