Scientists believe they could be a step closer to developing a new way of stopping the transmission of HIV without using condoms.

The microbicide gel was tested on macaque monkeys

Researchers from the US and Britain found for the first time that a microbicide - a chemical that kills microorganisms - can block the spread of the virus which can lead to Aids.

Correspondents say the research - published in the Journal Nature Medicine - could eventually benefit women whose partners refuse to use condoms.

Recent figures show that women are being hit hardest by the HIV epidemic, with the number of women infected with the virus increasing steadily worldwide.

Simian tests

The microbicides - possibly in the form of gels, foam sponges or pessaries - could be used by women before sexual intercourse.

HIV/Aids epidemic

Total number of people with HIV/Aids 42 million Women with HIV/Aids19.2 million Under-15s with HIV/Aids: 3.2 million Aids-related deaths in 2002: 3.1 million Figures from Dec 2002 - UNAids

They work to stop the virus from getting near the vulnerable cells it infects and increasing the body's defences.

In this case, the scientists applied a microbicide gel which contained a human antibody in the vaginas of macaque monkeys.

They found that the gel protected the macaques from infection with the simian HIV virus for more than seven hours.

Wider protection

It is estimated there are now two million more women with HIV in Africa than men.

This is despite the fact that Aids agencies believe that more than half of all women in sub-Saharan Africa tend to have only one sexual partner - most often their husband.

They are at risk of infection if their partners are not monogamous and if they refuse to use condoms.

Specialists say that microbicides offer more choice and control than other HIV barriers.

Among other things, they remove the stigma which is often attached to using condoms.

Research has shown that women and their partners in both the developed and the developing world want this type of product for HIV prevention.

BBC science reporter Ania Lichtarowicz says microbicides could also help women in industrialised countries.

Some of the 60 compounds now being tested can also be used as contraceptives, while others protect against sexually transmitted diseases like chlamydia and gonorrhoea - which are growing problems in developed countries.