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Origin of AIDS Virus

Less than 20 years ago, one of the modern menaces facing human culture was still unknown. It may seem remarkable that a new pathogen could suddenly appear “out of nowhere” and cause such devastation. Where did the human immunodeficiency virus come from? The answer to that question represents’ another of the mysteries surrounding AIDS. It is also a question that must be answered before we can eradicate this disease from our planet. The epidemic will not be controlled until all reservoirs are eliminated, including any still viable reservoir that harbored the virus before it entered the human population. Some scientists fear that these reservoirs may reintroduce the virus if it is eliminated from the human population.

Scientific evidence suggests that HIV evolved from similar viruses that infect monkeys and apes, although no virus identical to either of the HIV serotypes has been isolated from either of these primates. Genetic analysis however, has shown that HIV-2, the predominant form of the virus in the African population, shares at least 80% genetic homology with a virus found in the sooty mangabey, a West African monkey. There are several ways in which the virus may have been transmitted from the monkey to the human population in that area of the world. For example, monkeys are often caught for food and are butchered with few sanitary precautions. The virus could have easily been introduced into the cook who cut himself while preparing the monkeys carcass. Some monkeys are kept as pets or trapped for export. Scratches or bites may have introduced the virus into pet owners.
The reservoir of HIV-1 is less clear. So far the most closely related simian virus has been detected only in chimpanzees, but the two viruses are so dissimilar that it is questionable whether chimps are the recent source of human HIV-1. Perhaps an accidental inoculation occurred years ago and the human and animals viruses evolved along different paths. The original virus, for example, may not have been well adapted for human transmission or disease. There is evidence that immunodeficiency viruses will vary in pathogencity depending on the species infected. Sooty mangabey virus, for example, does not cause disease in the monkey but does cause disease if transferred to Asian macaques. Some have suggested that simian blood was transferred to humans as part f malaria experiments earlier in the century. “Other point to polio vaccines prepared in monkey kidney cell culture (there is no evidence to support this claim). It is also possible that HIV-1 entered both the chimpanzee and human populations from another as yet unidentified source.

If the human immunodeficiency viruses are derived from simian viruses, can AIDS be eradicated or controlled even with the development of a vaccine and effective chemotherapy? Some researchers are convinced that until we understand the dynamics of primate-to-human viral transmission, we are seriously handicapped in our ability to stop the introduction of new human pathogens, which may be continuing at a significant rate.
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