A global medical forum on AIDS opened Sunday in Rome, bringing together thousands of scientists, researchers and health experts.

The conference, sponsored by the International AIDS Society, is expected to be dominated by last week's announcement of a possible breakthrough in preventing the spread of the HIV virus, which causes AIDS.

Two new studies, released last Wednesday, show that drugs designed to treat HIV can also help prevent people from contracting the virus. The U.S.-led studies found that taking daily doses of HIV medication reduced the risk of infection in heterosexuals.

A previous study had already shown treatment reduced HIV transmission among gay men. But these new findings were

the first to show a daily oral dose of antiretroviral drugs is effective among heterosexuals.

The conference in Rome will last four days and is being attended by top officials, including the head of the United Nations AIDS agency .