The AIDS lentivirus from the family of retroviruses has puzzled the scientists since the illness came to limelight in the early 1980s. Its origin has been blamed on apes and chimpanzees. Its spread blames to an irresponsibly handled vaccine program, to biological weapons, to a promiscuous flight attendant. But where did it truly originate?
Numerous gay men in the USA began to develop cancers and stubborn opportunistic infections resistant to any treatment. There were various repeated cases of certain symptoms - but this syndrome hadn't been christened yet. As the number of cases increased, the curiosity of the medical scientists piqued; research into the causes of this syndrome, lead to the discovery of the Human Immunodeficiency Virus (HIV).
The How:
The HIV, like all viruses, attacks the Immune System. It is a lentivirus - lenti means slow, hence it is a slow virus. This means it takes a long period of time to manifest any adverse effects on the host's body. These viruses have been found in domestic animals, but the lentivirus which provided most information into the HIV mystery is the Simian Immunodeficiency Virus(SIV); simian means higher primates. Could it be that the jump of the SIV from our cousins (who differ only by 2% of genetic material from us) has occurred? Could it be that the SIV mutated and infected humans? The Mystery remains. However this is the generally accepted theory as the HIV1 and HIV2 viruses closely resemble to certain SIV strains.
In 1999, Nature magazine published a paper on a 10-year study by Dr Beatrice Hahn of the University of Alabama and Dr Paul Sharp of Nottingham University. It said that the HIV1 was similar to SIVcpz virus found in chimpanzees of Western Africa, known as Pan troglodytes. They had studied this particular strain that was identified in the frozen sample taken from a captive member of these chimpanzees and this sample proved that these SIVcpz could be the source of HIV1, they could have at some point mutated or crossed species from chimpanzees to humans. The HIV2 was suggested to be the hybrid of the SIVsm and SIVcpz that infected red-capped Mangabeys and greater spot-nosed monkeys, after they had hunted and fed on two smaller species of monkeys. Viruses can cross over species and this phenomenon, is known as Zoonosis. Five Zoonosis theories have been suggested - the Contaminated Needle Theory, the Hunter Theory, the Oral Polio Vaccine Theory, the Colonialism Theory, last but not the least, the Conspiracy Theory.
Also, Susan S, Hunter, in 2003 published her book called Black Death: AIDS in Africa, wherein she compares epidemic of AIDS with the ravaging of the Maya and Incas of Mesoamerica by smallpox brought by Spanish conquistadors and Percales' death by plague in Athens and its effect on the Peloponnesian War. She says that the AIDS epidemic was sequestered in Africa but as our world is well-connected and well-traveled it has reached every continent and has become a pandemic, instead of remaining an epidemic.