Birthplace of AIDS found

May 29 2006

After a 10-year search for the origin of HIV, scientists say they have finally traced the initial source of the global pandemic presently affecting more than 40-million people worldwide.

Researchers believe that back in the 1930's two colonies of chimpanzees in the south-east Cameroon is where the virus first jumped species from chimpanzees to humans, way before HIV began its devastating spread among people.

The finding provides a crucial link between HIV, which causes AIDS in humans, and the simian immunodeficiency virus (SIV), a strikingly similar virus that infects monkeys and chimpanzees.

HIV destroys the immune system and those infected are left vulnerable to wide range of diseases and infections and it was in those days difficult to diagnose.

Scientists suspect it was first carried by people travelling along the rivers and surreptitiously spread to Kinshasa, where the first human epidemic began to grow.

Researchers believe the virus infected humans and was gradually spread by river travel as all the rivers in Cameroon run into the Sangha, which joins the Congo River running past Kinshasa.

A team of researchers at Nottingham University joined forces with scientists in Montpellier and Alabama to search for signs of the virus in 10 chimpanzee populations throughout Cameroon, where SIV was known to be circulating.

Two different subspecies of chimpanzee call Cameroon home and the country is naturally divided into north and south by the Sanaga River.

While tests on chimpanzee faeces found north of the river showed no traces of SIV, it was found in colonies immediately on the southern side.

Beatrice Hahn, a virologist at the University of Alabama-Birmingham and the researchers located two colonies, living deep in the south-east corner of the country near the Ngoko River bordering the Democratic Republic of Congo.

They collected 599 samples of chimpanzee feces from 10 forest sites in the southern region of Cameroon and tested them for SIV and found that chimpanzee faeces had an SIV very similar to the HIV that causes AIDS in humans.

The scientists say that in some communities they detected SIV specific antibodies and viral genetic information in as many as 35% of chimps.

Professor Paul Sharp, a genetics expert at Nottingham University says the discovery represents the last piece of the puzzle; he says the viruses in south-east Cameroon are so close to HIV that it is difficult to envisage there could be any which could be closer and this is probably where HIV started.

Over the years researchers have offered various theories as to how the virus jumped to humans, but the commonly held belief is that hunters became infected when they caught and butchered infected chimps and as SIV appears to cause no outward signs of illness, they were unaware of it.

Sharp says chimps and humans are extremely similar genetically, and yet a virus that is seemingly harmless in chimps, jumps into humans and suddenly causes AIDS.

In order for SIV to cause a pandemic in humans, it would have first mutated into a form that could readily be picked up from infected chimpanzees and then adapted until it was infectious enough to be passed from person to person.

The first positively identified case of AIDS was reported in the United States in 1981, but epidemiologists believe that by the 1960s as many as 2,000 people in Africa may already have had AIDS.

1980 saw some one million people infected, and the virus was officially named a year later.

Of the 40-million people living with HIV now, more than two-thirds are in sub-Saharan Africa, where 77% of the women with HIV also live.

The spread of the disease has been relentless and last year alone there were nearly five million new HIV infections, 4.2-million among adults and 700,000 in children under 15 along with 3.1-million deaths from AIDS, more than half a million of whom were children.

Identifying the source of the HIV pandemic represents far more than finding the last piece of a puzzle and an understanding of how the virus infects chimpanzees.

Why it does not appear to cause disease in such a similar genetic species, could reveal useful clues about how the virus works in humans and what happened to the virus when it made the leap to humans.

The research appears in the journal Science.