First introduced in 1987, anti-retroviral drugs—ARVs for short—block H.I.V.'s assault on the body's immune system.
Silvia Ng'andwe, 28, in late March 2007, Zambia. Below, Silvia after just 40 days on anti-retroviral drugs. Photographs by Antonin Kratochvil.
on a hilltop on the outskirts of Rwanda's capital, Kigali, where some 7 percent of the population is infected with H.I.V., the human retrovirus that causes aids.