The two viruses that cause AIDS, HIV-1 and HIV-2, crossed over into the human population on at least 10 separate occasions during the 20th century
Gus Cairns:
But the vast majority of the world’s HIV epidemic arose from a single transmission event between an unknown chimpanzee and an unknown human in a small corner of south-east Cameroon, the conference said.
Paul Sharp of the University of Nottingham told the conference that he had narrowed down the chimpanzee equivalent of the virus that gave rise to most of the worldwide AIDS epidemic – the HIV-1 M subtype – to a small population of wild chimpanzees living in Cameroon close to the borders of the Republic of Congo and the Central African Republic.
This area is directly connected by river to Kinshasa, the capital of the Democratic Republic of Congo, where the first sample of blood containing human HIV was isolated in 1959 and where HIV in the human population continues to show the widest diversity today.
Sharp explained that HIV comes in two varieties as different as cats and dogs – HIV-1 and HIV-2. HIV-2, which is less easy to catch and causes a milder version of AIDS, is restricted to west Africa and is pretty much the same as the simian or monkey immunodeficiency virus (SIV) found in the sooty mangabey monkey.
HIV-2 seems to have crossed into humans at least seven times, but five of these genetically distinct versions of HIV-2 have only ever been found in one human apiece, showing that monkey-to-human virus transition may be a relatively common phenomenon but rarely gives rise to an epidemic.
The variety of HIV-2 found in almost all human cases (it remains concentrated in west Africa and among west African immigrants in countries like Portugal) has been found in sooty mangabeys in a forest in the south-west corner of the Ivory Coast.
When it comes to HIV-1, which causes most of the world’s AIDS, it was already known that it came from the SIV carried by chimpanzees, and that this SIV was itself a mixture of viruses carried by two other kinds of monkey.
Sharp’s team narrowed human-style HIV-1 in chimps down to the subspecies that lives in central west Africa in countries like the Republic of Congo (not the Democratic Republic, which lies on the other side of the Congo River), Gabon, and southern Cameroon.
They also knew that HIV-1 must have crossed into humans at least three times because it exists in three varieties called M, N and O – the latter two being rare.
Sharp’s team went to west Africa and spent months collecting droppings from wild chimps and testing them for SIV. They found SIV of the type that crossed into humans only existed among chimps in southern Cameroon. They found type N in one site in the centre of the country. And they found type M – M for mainstream, which infects 40 million humans today – in two sites in the extreme south-east of the country.
Sharp showed on a map that there is a direct river connection between that area and Kinshasa.
His team is also narrowing in on the specific genetic mutation which, they believe, enables SIV viruses to change their nature so they can infect humans.
By comparing human and chimp type M viruses he found a single genetic change in the HIV matrix protein, produced by a viral gene called gag, where the amino acid methionine in chimps has been replaced by arginine in humans.
When he re-infected chimps with human HIV, the amino acid switched straight back to the chimp version.
He also found that – even though they are quite different species of virus – exactly the same mutation has happened in HIV-2, and speculates that this crucial change is what enables SIV viruses to infect humans.
Exactly what this part of the matrix protein does in HIV is as yet unclear, but it appears to interact with human proteins and subvert natural antiviral defences.
If Sharp’s team can find out exactly, they might find a defence against the cellular machinery that enabled SIV to invade humans and spark off a worldwide epidemic about 50-60 years ago.
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posted by Adam Lawson @ 3:33 PM
3 comments
3 Comments:
This fits with my theory that General De Gaulle's bizarre attempt to conscript a black army in the Congo, during WWII, set off the epidemic. When a new pathogen is very rare, it will likely need some huge, unnatural amplifying factor to get it established. De Gaulle planned to march his army of draftees across the Sahara, showing the mad ruthlessness and scorn for their needs that he had. Any survivors of this exercise, who left blood samples in France or elsewhere, as from the 1960's or later, could be searched for and tested. Science should want to know how this happened, not be afraid of some group taking blame. Now we have some scientists who are brave in researching the exact zero point of the start of the epidemic.
I worked{lived] in Africa for seven years-Nigeria,Uganda,Sudan,Chad,Benin,and more-mainly west and central Africa.The initial outbreak of Lasa fever,as we became aware,ocurred in1971,then there was a virus deemed "green monkey fever",finally collectively called AIDS.It only came to prominence when a faggot Air France steward introduced it into Canada/NY in 1972,and the CDC became involved.One has to be aware of African mores to understand the following.If you don't know what "on the down low"means,forget it. In Africa,believe it or not,virginity in females is highly regarded,and the little males usually have an alternate source-a monkey just outside the compound,tied to a tree/stake for such purposes.If the monkey is pissed,it's easier to use one of your peer group[any thing you do before manhood]does not count.
There is little so rewarding as having respectable company expend efforts to juxtapose themselves to one's opinions.
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