- NEW YORK (Reuters
Health) - The scientists who first reported evidence that the HIV epidemic
got its start in west-central African chimpanzees have found that the monkey
counterpart to HIV does occur in chimps in the wild--but perhaps only rarely.
- Dr. Beatrice H. Hahn and her colleagues had previously
found that the west-central African chimpanzee subspecies Pan troglodytes
(P. t.) troglodytes harbor strains of simian immunodeficiency virus (SIV)
that are closely related genetically to HIV.
- Researchers had long suspected that HIV arose as a result
of a viral ``cross-species jump'' from primates to humans. The theory is
that, through contact with chimpanzee blood--possibly through hunting them
and eating the meat--humans were exposed to SIV. Some scientists speculate
the HIV epidemic took off in Africa due to modern-day cultural changes
such as increased population movement and breakdowns in traditional lifestyles.
- Hahn told Reuters Health that her team's new finding
''confirms and extends'' the belief that an African chimp population--most
likely the west-central population--are the origin of HIV.
- Their original finding of the HIV-related SIV strains,
called SIVcpz, were confined to chimpanzees in captivity, she explained.
- ``Our critics,'' she said, ``rightfully pointed out that
we have no clue what's going on in the wild.''
- In looking at urine and fecal samples from 58 wild chimpanzees
in three African nations, her team found that SIVcpz does occur in the
wild. But they found it in only one chimp, according to the report published
in the January 18th issue of Science.
- This one chimp lived in Gombe National Park in Tanzania,
in the easternmost part of the chimpanzee range, the researchers report.
The animal was also a member of the subspecies P. t. schweinfurthii--meaning,
Hahn said, that her team's original findings have been extended to another
African region and another chimp subspecies.
- But the very low incidence of SIVcpz her team found was
''surprising,'' Hahn said.
- She pointed to some possible explanations, however. For
one, SIVcpz, by all appearances, does not spread very ''efficiently'' among
chimps--a point that Hahn said will be the subject of more study.
- And, she added, Gombe National Park, where the new case
was found, has been isolated ``like an island'' for the past decade or
so. This fact, coupled with a sharp decline in the chimp population, suggest
that SIVcpz could have recently become uncommon in this region.
- ``We don't know what it was like 50 years ago,'' Hahn
- But there is no indication that chimps in this area might
be the origin of the current HIV epidemic. Hahn's team found that the Gombe
chimp's strain of SIVcpz was quite different from both the west-central
African SIV strains and the major HIV groups.
- She said she believes the west-central chimps remain
the ''most likely'' source of HIV.
- SOURCE: Science 2002;295:465.