In a study launched on Tuesday, researchers want to find out whether antiretroviral drugs normally used by people already carrying the HIV virus could protect those at higher risk of infection, a concept referred to as pre-exposure prophylaxis (PrEP).

"It's early days but very exciting. It's another strategy, it gives us hope that maybe we can beat this epidemic," researcher Linda-Gail Bekker told Reuters at the sidelines of the launch of the study.

The study targets men who have sex with other men because they have been found to be at higher risk of HIV infection than other sexual groups.

South Africa has one of the world's highest incidences of the HIV virus which can lead to AIDS, with an estimated 500,000 people infected each year. About 1,000 die every day from AIDS-related illnesses.

"In terms of concept ... it (PrEP) looks like it has a chance of working," Bekker said, likening it to oral contraceptives used to help prevent pregnancy.

"I'm not sure that it's going to be the silver bullet, I doubt that. I think its going to be, hopefully, another strategy in our armour," she added.

South Africa is the only African country selected to participate in the international study, which includes Brazil, Ecuador, Peru, Thailand and the United States.

Results from the global PrEP study, which will enrol 3,000 high risk men who have sex with men, is expected towards the end of 2010.