By DAGI KIMANI
Kenya's apparently HIV-resistant commercial sex workers have their genes to thank for it, a report presented at the 16th International Aids Conference in Toronto says.
According to the report by researchers from the University of Manitoba, genetic variations explain why the sex workers continue to be Aids-free despite engaging in extremely high-risk behaviour, even as some of their colleagues succumb to the disease. The report was based on follow-up studies of more than 850 commercial sex workers at the Nairobi Majengo slum, historically the city's red light district.
Over a three-year period, most of the women became HIV-positive but at least 130 remained negative despite each having unprotected sex with at least 500 men. Some of the sex workers, research data compiled by University of Nairobi researchers says, routinely have as many as 30 clients in a day.
According to the report presented in Toronto, the sex workers protection may be based on a gene called human leukocyte antigen-G, or HLA-G, which helps the immune system recognise viruses such as HIV.
Discovery of the infection-resistant commercial sex workers in the late 1990s led to the development of a test vaccine by researchers drawn from the universities of Nairobi, Oxford and Manitoba. The test vaccine was subsequently tested in dozens of volunteers in both Kenya and Britain. In 2004, researchers involved in the project announced that although the trial vaccine had been found to elicit some immune response, this was not enough to make it clinically viable.
Earlier, researchers involved in the vaccine search said that the sex workers apparent immunity was due to an immune response involving killer-T cells, which are a specialised form of white blood cells that are particularly potent against disease-causing organisms. Continuous exposure to HIV on a daily basis due to multiple clients, the researchers theorised, made the immune systems of the sex workers produce high levels of killer-T cells, thus conferring immunity. The failed test vaccine was designed to provoke this reaction without the danger of actual infection.
The findings from Majengo that there could be a genetic basis for immunity against HIV will boost the unpublished theory that there are a significant number of people who are naturally immune to HIV, although these are far out-numbered by those who are susceptible. Natural immunity, Aids experts say, could explain the high number of long-term discordant couples in regions such as East Africa with high prevalence rates. Studies elsewhere have indicated that about 3 per cent of Caucasians cannot contract HIV even when exposed.
Elsewhere, the head of Kenya's National Aids and Sexually Transmitted Infections Control Programme (Nascop), Dr Ibrahim Mohammed last week attributed the dramatic decline in HIV prevalence rates to behaviour change among the country's youth, traditionally the most vulnerable group.
In a review paper authored together with Dr Mark Dybul, the US global Aids co-ordinator of the President's Emergency Plan for Aids Relief (Pepfar), Dr Mohammed said that faithfulness to one partner among men aged 20-24 years had risen dramatically between 1998 and 2003, with those reporting contact with more than one sexual partner in the past year declining from 35 to 18 per cent.