Simian source found for Aids



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, the capital of what is now the Democractic Republic of Congo (DRC), where the first human epidemic began to grow.


Cameroon is home to two subspecies of chimpanzee, separated by the the Sanaga river, which slices the country into north and south. North of the river, tests on chimpanzee faeces found no traces of SIV, but it was present in colonies immediately on the southern side.

As the search for the source of HIV moved further south, researchers located two colonies, living deep in the southeast corner of the country near the Ngoko river bordering the DRC.Tests on chimpanzee faeces here revealed an SIV strikingly similar to the HIV that causes Aids in humans. In some communities they detected SIV-specific antibodies and viral genetic information in as many as 35% of chimps.

"For us, this is really the last piece of the puzzle," said Paul Sharp, a professor of genetics at Nottingham University. "This is where it probably all started. We've got these viruses in southeast Cameroon, which are so close to HIV, and it's difficult to envisage there could be any which could be closer." The research appeared in the journal Science last month.

Researchers have various theories on how the virus jumped to humans. The most widely held view is that hunters became infected when they caught and butchered infected chimps. SIV appears to cause no outward signs of illness, so hunters would not have known if they were catching infected animals.



Researchers believe that 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 built up in the human population.


The first clearly identified case of Aids reported in the United States was in 1981, though it seems an African-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 2,000 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.

Last year there were nearly 5m new HIV infections, 4.2m among adults and 700,000 in children under 15. In the same year there were 3.1m deaths from Aids, more than half a million of whom were children.

Identifying the source of the HIV pandemic is more than filling in a missing link in the disease's progression. Understanding how the virus infects chimpanzees, and why it does not appear to cause disease in such a similar genetic species, could provide clues about how the virus works in humans and which changes happened to the virus when it made the leap to humans.