Explanation AIDS is believed to have originated in Central Africa. Studies have indicated that HIV is closely related to a chimpanzee virus and may have been introduced to humans in Central Africa from the chimpanzees. AIDS was first recognized in USA in 1981 and the causal agent, HIV, was identified by laboratories in France and USA soon. It has subsequently been identified in 71 countries throughout the world. It was estimated that 23 million people were infected with HIV in 1995. As of today (2003) about 34.3 million people worldwide are living with HIV/AIDS. HIV is an RNA virus that replicates inside human cells by first making DNA copies of itself. HIV binds to the CD4 receptor present on macrophages and T lymphocytes. The viral RNA enters the host cell and is transcribed by the enzyme Reverse Transcriptase into DNA. The viral DNA is incorporated into the chromosomal DNA of the host. The viral DNA may remain dormant for sometime and then suddenly produce new HIV particles, which are budded off the infected host cell. The viruses spread and infect many other T lymphocytes and eventually kill them. This destruction of the body's T cells damage the immune response resulting in the onset of AIDS, with cancers and opportunistic infections, free to attack the defenceless individual. A blood test is used to determine whether a person is HIV infected or not. Persons infected with HIV go through 4 phases: After infection by HIV, the first phase is characterized by flu-like illness; skin rash and swollen lymph nodes. The second phase is characterized by the antibody positive phase or HIV positive phase. This is the phase between infection and the onset of clinical symptoms. This period may last from a few weeks to ten or more years. The third phase is characterized by AIDS-related complex (ARC). At this stage the patient may succumb to a variety of 'opportunistic' infections like common bacterial, viral and fungal infections. But the infections are not life threatening. Loss of body weight may be seen up to 10% of body mass. Diseases of organs and the development of secondary cancers characterize the fourth phase. Opportunistic infections caused by protozoa, virus, bacteria and fungus occurs, which fail to heal. Some individuals may lose a great deal of weight. The fourth phase shows onset of AIDS, the patient requires hospitalization and very few patients survive longer than five years. The risk of HIV transmission from an infected individual to a healthy individual during the course of day-to-day contact is essentially non-existent. An effective vaccine to combat HIV is yet to be developed. The virus has the ability to change its genetic structure, which alters the proteins on the surface of the virus that the antibodies recognize, thus making it difficult to develop a vaccine. The drug AZT (Azidothymidine) inhibits virus replication and has helped a number of patients. But it has side effects. As of today, prevention of HIV infection is the only answer to AIDS. Suggested preventive methods are: Taking adequate protection (such as using condoms) during intimate sexual relationship. Absence of promiscuity and restriction to one sexual partner to reduce the risk of infection Usage of sterilized disposable needles. Always using blood from registered blood banks. AIDS is not transmitted by: Shaking hands Eating with HIV infected individuals Contact with clothing and other articles used by an HIV infected person Sharing toilets and bathrooms with HIV infected individuals.