Effect of Tenofovir on Genital Herpes Simplex Virus (HSV) Shedding

Inclusion Criteria: * Women age 18-50 * HSV-2 seropositive by the University of Washington (UW) Western blot * History of recurrent genital herpes, with more than 4 recurrences but less than 10 in the last year or, if currently on suppressive therapy, with more than 4 recurrences but less than 10 in the year prior to starting suppressive therapy * HIV negative * General good health * Willing to not use antiviral therapy (other than the study drug) for the duration of the study * Willing to obtain a swab from genital secretions twice daily for the duration of the study * Willing to use effective birth control * Able to provide written informed consent at screening and enrollment Exclusion Criteria: * HIV positive or at high risk for HIV acquisition (intravenous drug user or HIV+ sex partner) * Hepatitis B (HepB) antigen (Ag) positive, or at high risk for HepB acquisition and not vaccinated * Have a history of adverse reaction to tenofovir and/or adefovir * Immunosuppressive medications, except for intranasal or topical (not high potency) steroids. * Any kidney disease, or renal insufficiency, defined as serum creatinine \>1.5 mg/dl. Participants with a prior history of a single episode of pyelonephritis will be eligible. * Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \> 3 times upper limit of normal * Pregnancy, as confirmed by a urine pregnancy test, planning to become pregnant during the course of the trial, or breast-feeding. * Serious medical conditions or active infections * Any other conditions that in the judgment of the investigator would preclude successful completion of the clinical trial.