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The first case of the human immunodeficiency virus (HIV) was
reported in the USA in 1981. However, research into the origin of
the disease has since shown that the virus was present in man long
before it was documented.
HIV belongs to the lentivirus family of retroviruses. Lentiviruses
are characterised as slow-growing viruses and normally found in
non-human primates (monkeys). One of the lentiviruses found in
monkeys is the simian immunodeficiency virus (SIV). Research on the
human immunodeficiency virus has found a close resemblance to the
simian immunodeficiency virus.
Studies on chimpanzees in the 1980s to determine if a link existed
between the viruses showed that when deliberately injected with
HIV, the monkeys did not develop HIV/AIDS. In 1999, a clear link
was established between SIV and HIV based on genetic testing
performed on frozen blood and tissue samples taken from a
sub-species of chimpanzee (found in central-west Africa).
In other research, the presence of the HIV infection in humans was
found in a blood sample dating back to 1959, and in separate tissue
samples taken in 1969 and 1976. However, it is not known why HIV
did not emerge then. Some researchers believe that in the 1970s
there was an event or series of events in the mutation of the virus
within humans that changed its structure to become a virulent
deadly virus.
Combined, these scientific findings form the basis of the current
theory that SIV crossed over from monkey to man (perhaps on
numerous occasions) sometime earlier in the 20th century and
mutated within man and emerged as the human immunodeficiency virus.
How and when it passed between the species is not known.
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