Giving women the power to shield themselves from HIV could prove to be the turning point in the battle against Aids, the philanthropist Bill Gates has told a global conference on the disease.

One way to do this would be to give women access to a microbicidal gel or cream which they could administer without anyone knowing to protect themselves from transmission of the virus, the Microsoft founder said.

The Bill and Melinda Gates Foundation, which Mr Gates runs with his wife, has so far contributed $1.9 billion (£1 billion) and recently announced a further $500 million grant to a Geneva-based fund that helps those suffering from the virus.

Mr Gates told the opening session of the 16th International Aids Conference in Toronto, which has attracted 24,000 scientists, activists and health workers, that the search for a vaccine to prevent the HIV virus, and universal treatment of those infected, remained his foundation's top priorities.

“At the same time, we have to understand that the goal of universal treatment - or even the more modest goal of significantly increasing the percentage of people who get treatment - cannot happen unless we dramatically reduce the rate of new infections,” he said.

"We want to call on everyone here and around the world to help speed up what we hope will be the next big breakthrough in the fight against Aids – the discovery of a microbicide or an oral prevention drug that can block the transmission of HIV."

"This could mark a turning point in the epidemic, and we have to make it an urgent priority."

Sixteen microbicides, usually vaginal gels or creams that help kill block sexually transmitted diseases, are currently undergoing clinical evaluation against HIV,five of them in major advanced studies.

They range from gels based on carrageenan, taken from sea algae and already used widely in foods and toiletries, to HIV drugs put into a gel or cream that could be applied vaginally.

Researchers hope that the first successful cream could be available as soon as 2009, so women could protect themselves without having to ask their husbands or partners to use a condom or to abstain from sex.

"We need to put the power to prevent HIV in the hands of women," Mr Gates said. "We are determined to help medical science discover these new drugs and get them to the people who need them."

Both Mr and Mrs Gates have called for greater advocacy to break the stigma of HIV/Aids for women in impoverished nations. He said that he would step up funding for research into preventative measures and asked governments and other donors to do the same.

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