In Peru, Andean leishmaniasis affects agricultural populations of the slopes and valleys of the Western Andes. Treatment of lesions with drugs is a difficult, lengthy, and expensive process, often requiring hospitalization. Drastic and painful practices causing disfiguration are used. The transmission of the disease is related to the working habits of the population. Farmers and their families travel to their fields and remain there for varying periods of time (ranging from several days to several weeks) using provisional shelters. As these shelters are open, people are exposed to sandfly bites. Peak rates of transmission occur while people are in the crop fields. Disease transmission is intensely focused near ravines scattered throughout agricultural land and grazing fields. These ravines, conspicuous for being rocky and having sparse vegetation and few trees, are resting places for sandflies. There is evidence that indicates a marked decrease in sandfly population after the planting of eucalyptus trees.