[BRIEF NOTE] HIV-1 kills chimpanzees

[rfmcdonald]

The fact reported in the title of Michael L. Wilson's recent New York Times article, "Study Finds Chimps Die From Simian AIDS, Dispelling Widely Held Belief", isn't all that surprising.

The finding upsets a widely held scientific belief that chimpanzees, the closest relatives to humans, can get the virus that causes simian AIDS but without harm.

It also suggests that an outbreak of AIDS is contributing to the declining chimpanzee population in Africa, said the leader of the research team, Dr. Beatrice Hahn of the University of Alabama at Birmingham.

She said that comparisons of the viruses that cause AIDS in chimpanzees and humans could lead to new insights into the responses of the immune systems in both species.

“Our findings allow us to look at H.I.V. from a new angle, comparing and contrasting chimpanzee and human infections,” Dr. Hahn said in an interview. Her team’s study is being reported in the journal Nature on Thursday.

As researchers conducted autopsies on the bodies of the dead chimps they could find, they detected evidence of organ and tissue damage similar to that in late-stage human AIDS. Infected chimpanzees were also found to have a 10 to 16 times greater risk of dying than uninfected ones. Infected females were less likely to give birth. If they did, they could pass the virus to their infants, and they had a higher infant death rate than that of uninfected females.

[. . .]

The simian virus, known as S.I.V.cpz, is considered the precursor of H.I.V.-1, which crossed the species barrier sometime in the past 100 years.

“We cannot date exactly when chimpanzees first got infected, but we certainly suspect that it was much, much longer than 100 years ago,” Dr. Hahn said. “Our gut feeling is that the chimp virus infection is not quite as” damaging as H.I.V.-1 is in humans. The difference in the way the virus damages tissue, she said, “leads us to speculate that chimps may be one step ahead in adapting to the virus, and identifying that step would be important.”

More than 40 simian immunodeficiency viruses are known to infect African primates. African monkeys infected with the virus that causes simian AIDS have rarely developed AIDS. Only seven chimpanzees naturally infected with S.I.V.cpz have been studied in captivity, and five of them died of unknown causes as infants. The only chimpanzee that was naturally infected with the simian virus and underwent standard virological and immunological tests showed none of the typical damage of AIDS, like low CD-4 cell counts and damaged lymph nodes. Two other chimpanzees injected with S.I.V.cpz in captivity did not show such changes.

The simian immunodeficiency virus is ultimately the source of the various human immunodeficiency viruses, with more than forty different variants. The two major types of HIV producing the HIV/AIDS epidemic are HIV-1 and HIV-2, originating in viruses hosted by chimpanzee and sooty mangabeys. HIV-2 is a virus indigenous to West Africa's primate population, apparently introduced throughout Guinea-Bissau in the 1960s by Portuguese medical campaigns. HIV-2 tends to be less virulent than HIV-1, more difficult to transmit than HIV-1, the viral strain largely responsible for the AIDS epidemic; in fact, HIV-2 is limited primarily to West Africa and former Portuguese colonies, HIV-1 dominating elsewhere.

If a virus is more virulent in humans, it's not very surprising that its more virulent in the chimpanzees from which the virus originated. To me, a non-biologist somewhat familiar with HIV and AIDS, that is.