Human immune deficiency virus (HIV) is closely related to the
simian immunodeficiency virus which is found in monkeys
and apes. HIV-I is closely related to the strains of SIV found in
chimpanzees, and HIV-II is closely related to the strains of SIV
found in the sooty mangabeys. In 1999 some scientists
found a strain of SIV ( called SIVcpz) in chimpanzees that was
closely related to HIV-I in humans. It was then concluded that
this proved that chimpanzees were the source of HIV-I and
had crossed species to humans at some point in time. Furthermore
it was thought that these chimpanzees got the SIV
virus by eating two smaller monkeys (red-capped mangabeys
and greater spot nosed monkeys) and became infected with
two strains of SIV. These two strains joined together to form
the SIVcpz strain which has the ability to infect humans.
This was followed by the concept of the hunter who ate these
chimpanzees and became infected or the viruses were able to
access the hunter through wounds and cuts. Ocassionally the
hunter would be able to ‘fight’ off this SIV, but sometimes they
were able to survive in humans as HIV.
HIV-II comes from SIVsmm in sooty mangabey monkeys rather
than chimpanzees. The crossover to humans is believed to
have happened in a similar way (through the killing and consumption
of monkey meat).
It is far rarer, and less infectious than HIV-1. As a result, it infects
far fewer people, and is mainly found in a few countries
in West Africa like Mali, Mauritania, Nigeria and Sierra Leone. There are four groups of HIV strains M,N,O,P with M being
the most common with nine subtypes (A-D,F-H,J,K). There are
so many strains because in the attempt to enter and adapt to
survive within the human system the SIV had to evolve into
several strains the most successful being able to survive the
new environment.
Researchers have come to the conclusion that this “zoonotic”
infection of humans with this virus started around 1920 in the
Democratic Republic of Congo. The same area is known for
having the most genetic diversity in HIV strains than anywhere
else, reflecting the number of different times SIV was passed
to humans. Many of the first cases of AIDS were recorded
there too. The extensive transport routes in that part including
the railways, rivers and road networks together with the
high migrant population and growing sex trade all supported
the spread of the HIV virus. The lack of transport routes in the
north and east of the country accounted for the lower reports
of infections from these regions at the time. By 1980, half
of all infections in DR Congo were in locations outside of the
Kinshasa area, reflecting the growing epidemic.
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