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 Health & Beauty | May 2006 
Scientific Sleuths Trace HIV Back to Cameroon Chimps
 Ian Sample - The Age Company
| | This chimpanzee mother, in Tanzania, is SIV-positive. (AP) |
Scientists searching for the origin of HIV, the global pandemic infecting more than 40 million people, believe they have finally tracked its source to two colonies of chimpanzees in a corner of Cameroon.
The finding culminates a 10-year hunt for the source of the pandemic and provides a crucial link between HIV, which causes AIDS in humans, and the simian immunodeficiency virus (SIV), a similar virus that infects monkeys and chimpanzees.
Researchers believe the virus first jumped from chimpanzees to humans in south-eastern Cameroon before HIV infection began spreading among people as far back as the 1930s.
At the time, HIV, which destroys the immune system, leaving those infected vulnerable to myriad diseases, was difficult to diagnose. Carried by people travelling along the rivers, it spread unnoticed to Kinshasa, where the first human epidemic began to grow.
Researchers at Nottingham University, England, joined scientists in Montpellier in France and Alabama in the US to search for signs of the virus in 10 chimpanzee populations throughout Cameroon, where SIV was known to circulate.
Cameroon is home to two subspecies of chimpanzee, separated by the Sanaga River, which slices the country into north and south. North of the river, faecal tests found no traces of SIV, but it was present in colonies to the south.
 As the search moved further south, researchers located two colonies in the south-east corner of the country near the Ngoko River bordering the Democratic Republic of Congo.
Tests on faeces here revealed an SIV strikingly similar to the HIV that causes AIDS. In some communities they detected SIV specific antibodies and viral genetic information in as many as 35 per cent of chimps.
"For us, this is really the last piece of the puzzle," said Paul Sharp, a professor of genetics at Nottingham. "This is where it probably all started. We've got these viruses in south-east Cameroon, which are so close to HIV, and it's difficult to envisage there could be any which could be closer."
Researchers have various theories on how the virus jumped to humans; the most widely held view is that hunters became infected when they butchered infected chimps. SIV appears to cause no outward signs of illness, so hunters would not have known if they were catching infected animals.
"When people hunt chimpanzees, they tend to butcher them on the spot and then there's a lot of blood flying around," said Professor Sharp. "If the hunter has any open wounds, then that's an opportunity to get infected."
"Chimps and humans are extremely similar genetically, but here we have a virus that is seemingly harmless in chimps, jumps into humans and suddenly causes AIDS."
Researchers believe the virus infected humans some time before the 1930s and was gradually spread by river travel. All of the rivers in Cameroon run into the Sangha, which joins the Congo River running past Kinshasa.
Trade along the routes could have spread the virus, which slowly built up in the human population.
For SIV to cause a pandemic in humans, it must have first mutated into a form that could readily be picked up from infected chimpanzees. Then it adapted until it was infectious enough to be passed from person to person.
The first clearly identified case of AIDS reported in the US was in 1981, though it seems an American teenager died of it in St Louis in 1969.
Epidemiologists who have studied the growth of the pandemic suggest that by the 1960s about 2000 people in Africa may have had HIV, which was as yet unnamed. By 1980, closer to 1 million people were infected, and the virus was named a year later.
Of the 40 million people living with HIV now, more than two-thirds are in sub-Saharan Africa, which is home to 77 per cent of the women with HIV.
Understanding how the virus infects chimpanzees could reveal clues about how it works in humans and what changes happened to the virus when it made the leap to humans. |
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