Prostitutes from the slum may hold key to Aids cure

Monica Marwa is a 25-year-old prostitute living in the notorious Majengo slum on the outskirts of the Kenyan capital, Nairobi. She charges between 30 and 50 Kenyan shillings (between 33 and 55 pence) for sex. There is nothing extraordinary about her line of work nor about her fees - it is estimated that more than half of the women in Majengo sell their bodies for such paltry rewards.

What is surprising is that, despite years of unprotected sex and exposure to the HIV virus, Monica seems to be immune to Aids.

Hers is one of some 40 similar cases in Majengo which scientists believe could hold the key to an Aids cure. In a programme bringing together the University of Nairobi with Oxford University and two universities in North America, researchers are mapping the genes of Majengo's HIV-resistant women in an effort to discover what it is that protects them from infection.

"We are taking blood from the HIV-negative women and their relatives as well as from some women who have tested positive," says Dr Ephantus Njagi, whose work at the Majengo clinic for commercial sex workers is at the forefront of the research programme. "At the moment we believe some women have a genetic make-up which enables them to produce something which kills off the virus.

"Eventually, we hope it will be possible to produce a vaccine which will immunise people against Aids."

HIV-resistance is considered the "hottest" area of Aids research. To date, most studies on the subject have been confined to homosexual men in the United States.

Nearly 1,900 commercial sex workers have been documented since the clinic at Majengo was opened just over 10 years ago. In that time, 400 of the women have died of Aids. More than 90 per cent of the clinic's clients are HIV-positive.

"I'm really surprised I'm negative," says Monica on the day she calls at the clinic for a biannual blood test. "When I started in 1991, I never asked the men to use a condom. I only began insisting on it in 1993. Quite a few of my friends have died of Aids. I thank God, I'm very lucky."

When Monica comes to the clinic she takes three cartons containing 144 condoms each. Although they are free, condom usage is estimated at only 70 per cent among Majengo's prostitutes.

Even the HIV-negative women are advised to use condoms as their immunity cannot be guaranteed.

Monica has an average of four or five clients a day though towards the end of the month, when workers are paid, that number can rise to 15 or 20 a day.

The evidence that HIV resistance could be genetic is persuasive. Two of the HIV-resistant women attending the clinic, categorised as Nos 887 and 893, are sisters. No 887 has three daughters, all prostitutes, who have consistently proved to be HIV-negative. No 893 has two daughters who work as prostitutes and are also HIV-negative.

Yet, resistance to the virus is not automatically inherited by all family members. Mastura Adam, anotherprostitute, is HIV-negative despite exposure to the virus. Both her aunt and her sister are sex workers. Yet while the former has proved immune to HIV infection, the latter is seropositive.

The HIV-resistant women at Majengo show no trace of the HIV antibodies normally associated with people who indulge in high-risk sexual behaviour. Yet they regularly become infected with sexually transmitted diseases so must also be frequently exposed to HIV. Cases like theirs are fuelling speculation that some people are genetically programmed to produce specialised cells which neutralise the virus after it enters their bodies.

It is estimated that in Kenya a million people - more than 7 per cent of the population - are HIV positive. In some areas of Nairobi, 20 to 30 per cent of women coming for prenatal check-ups are infected with the virus.