• Serologically confirmed HIV infection [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  

• Occurrence and frequency of genital ulcers [ Time Frame: Throughout study ] [ Designated as safety issue: Yes ]
  
• Proportion of doses missed by study participants assigned to twice-daily acyclovir and twice-daily placebo [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  

Many studies have shown that prior HSV-2 infection is associated with an increased risk for HIV infection. Acyclovir is the most widely studied and clinically utilized antiviral for the suppression of HSV-2 infection. This study will evaluate the efficacy of twice-daily dosing of acyclovir in preventing HIV infection in both WSM and MSM with genital herpes. For this study, WSM will be enrolled in Lusaka, Zambia; Harare, Zimbabwe; and Johannesburg, South Africa; MSM will be enrolled in Lima and Pucallpa, Peru; Seattle, Washington, USA; New York City, New York, USA; and San Francisco, California, USA.

Participants will be enrolled for 12 months in this study and will be randomly assigned to one of two study arms. The first arm will receive 400 mg acyclovir twice daily; the second arm will receive placebo. Follow-up visits will occur monthly. Participants will be tested for STDs, including HIV and syphilis, at each visit and treated as necessary; participants will also be given adherence and condom counseling, risk behavior and sexual history questionnaires, and genital symptoms questionnaires at all study visits. Medical history will be assessed and participants will undergo blood work at Months 3, 6, 9, and 12.