Aids expert warns of new threat

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Science Correspondent

A strain of HIV that is spreading fast among the prostitutes and other sex workers of South East Asia may be more prone to transmission between men and women than strains found in the UK, according to an Aids scientist who warns of the danger to Western heterosexuals.

Thailand, which has seen a dramatic rise in the number of men and women infected with HIV since the late 1980s, has come under intense scrutiny because there appear to be two epidemics, one among heterosexuals and one among intravenous drug users.

Whereas less than 10 per cent of HIV transmissions in the West involve heterosexuals, the situation is reversed in Thailand where it is estimated that as many as 1 million men and women out of the population of 60 million are HIV positive.

An analysis of the genetics of samples of HIV taken from different groups reveals that heterosexuals in Thailand are predominately infected with a strain known as subtype E and drug users with subtype B, which is also the main subtype found in the US and Europe.

Max Essex, a virologist at Harvard School of Public Health, believes he has found evidence for believing that subtype E is more readily transmitted during heterosexual sex, whereas subtype B is more prone to being passed on during anal sex. This, he said, could explain why the HIV epidemic in the West is predominantly among gay men.

His evidence is based on test-tube studies showing that subtype E more readily infects cells lining the vagina and the tip of the penis than subtype B.

The corollary is that if subtype E should gain a foothold in Britain, then heterosexual transmission of HIV could see a similar dramatic increase.

Dr Essex's theory, however, does not entirely fit with other facts of the global epidemic. There is an equally dramatic heterosexual spread of the virus in Africa, where there are many different subtypes other than E, and heterosexual transmission of HIV is also common in Brazil and South America, where subtype B predominates.

Simon Wain-Hobson, an HIV expert at the Pasteur Institute in Paris, said Dr Essex's ideas were no more than hypothesis at present. ''It seems to be premature to be drawing these conclusions,'' he said.