Date: Tue May 23 15:25:19 2000
Posted By: Brian Foley, Post-doc/Fellow Molecular Genetics
Area of science: Virology
ID: 957699075.Vi
Message:
The short answer is "YES".
The long answer is that there are actually several AIDS
viruses, and each of them came from a non-human primate. The
virus that is causing the main AIDS epidemic worldwide is the
HIV-1 M group virus, which most likely came from a subspecies of
chimpanzee. Two other chimpanzee viruses also jumped from chimp
to man, and became named HIV-1 O group and HIV-1 N group. The
HIV-1 O and N groups have not spread out of Africa very much.
HIV-2 came from sootey mangabeys, and just as there
were at least 3 transfers from chimps to humans to create
the 3 groups of HIV-1, there were at least 5 transfers from
sooty mangabeys to humans. Again only one of theose transfers
resulted in an epidemic, and the HIV-2 epidemic is quite small,
similar to the HIV-1 O group epidemic.
We don't yet know exactly how or when any of these
transfers from non-human primates to humans ocurred. Almost
everyone has a strong opinion about this, but nobody has any
real proof yet. Some of the strong opinions are not based on
any scientific evidence at all, and I won't discuss them here
in a science discussion. The ideas/opinions that do have some
basis in science include:
- The "cut hunter theory". Many people (both native
Africans and Europeans on safari) have killed and eaten many
different species of monkeys and apes. Eating the cooked meat would
not likley transfer a virus, but if a person cut himself or herself
and got monkey blood into the fresh would during the killing and
butchering process, viruses would be quite likely to transfer.
Arguments for this theory are that we know for sure that people do
kill and butcher many species of monkeys and apes, both to eat
them, and in the process of capturing them for zoos or pets or
other reasons. Arguments against it are that people have probably
been killing monkeys and apes for millions of years, and yet the
global AIDS epidemic seems to be less than 100 years old.
- The "oral polio vaccine theory". There was an oral
polio vaccine given to roughly 500,000 children and infants in
the Ruzizi valley (western boarder of Uganda/Rwanda/Burundi) in
1957-1959. The people who made this vaccine are known to
have used chimpanzees to test the vaccine, and the theory is that
they may have also used chimpanzees to develop the vaccine. If
they did use chimpanzee kidneys to grow the vaccine, the virus
could possibly have been in the vaccine, and if it was in the
vaccine, then children with bleeding mouths (just lost a tooth
for example) could have become infected. Arguments against this
are that it might possibly explain HIV-1 M group alone but that
still leaves us looking for the source of 2 other HIV-1 group
transfers and 6 HIV-2 transfers. Also, the origin of the HIV-1
M group appears to have been prior to 1940, and most likely
closer to Cameroon than to the Ruzizi valley. Arguements for it
are that we don't have any solid record of HIV-1 in humans before
1959 (the "before 1940" date is theoretical), and that it
is possible that HIV-2 and the other HIV-1 groups were caused by
other vaccines.
- The "coevolution theory". HIV-1 could have evolved
with humans over millions of years, just as SIV-CPZ evolved
with chimpanzees and SIV-AGM evolved with African green monkeys
and SIV-SMM evolved with sooty mangabeys. The similarity between
HIV-1 and SIV-CPZ could be because we are more similar to chimpanzees
than to other primates. This theory does not seem to be valid at
all, because again the AIDS epidemic seems to be less than 100 years
old, and HIV-2 was very clearly the result of at least 6 cross-species
transmisson events.
Even if we someday narrow down when and how the
different HIV-1 and HIV-2 strains were transferred from non-human
primates to humans, we will still be wondering when and how the
primates got the virus. It is clear that all lentiviruses are
related, and it is clear that either primates got the virus
from other mammals (goats, sheep, cattle [Asian buffalo and
domestic cattle], cats [lions, pumas, housecats, etc], horses,
and other species) or that the other mammals got the virus from
the primates. We can tell it was a single transfer, but we
can't tell which direction it went. We also cannot yet get even
a rough estimate of when the primate/other mammal transfer took
place. Viruses are too small to leave any fossils, and we don't
have a lentivirus from a wolley mammoth or other frozen ice-age
mammal to study yet. As far as I know, nobody has even looked
for one yet (they've found mammoths and sabertooth tigers, but
have not looked for viruses in them).
Brian Foley
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