MadSci Network: Virology

Re: Did the AIDS virus come from monkeys?

Date: Tue May 23 15:25:19 2000
Posted By: Brian Foley, Post-doc/Fellow Molecular Genetics
Area of science: Virology
ID: 957699075.Vi

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:

  1. 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.

  2. 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.

  3. 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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