Acyclovir, a widely used drug for treating genital herpes, is being tested to evaluate whether suppressing the sexually transmitted disease can reduce HIV transmission.

The Partners in Prevention study is being conducted on over 1 000 discordant couples - where one partner is HIV positive - at 12 sites, including UCT, in seven African countries. The number of couples is expected to increase to 3 000 this year.

The University of Washington is undertaking the study with funding from the Bill and Melinda Gates Foundation.

In Africa, research has found that 50% of HIV-negative and 80% of HIV positive persons have genital herpes, suggesting a strong link between the two infections.