American trypanosomiasis (Chagas disease) is an important cause of heart disease, megaesophagus and megacolon among people in Mexico, Central and South America. Many mammals can be infected with the parasite that causes this disease; however, among animals, clinical cases have been reported mainly in dogs. Chagas disease is transmitted by the bites of triatomine insects, or “kissing bugs.” Some infected insects occur in sylvatic environments, where humans are exposed only occasionally. These “sylvatic cycles” are found from the U.S. through South America. From Mexico through South America, triatomine insects have also become adapted to human dwellings, particularly substandard housing where the insects hide in cracks during the day and emerge to feed on humans and animals at night. Most human cases are acquired from insects in these “domestic cycles,” and campaigns to eliminate the bugs, together with testing to prevent congenital cases and transmission in blood transfusions, have significantly reduced the incidence of Chagas disease. Antiparasitic treatment is most effective early, before irreversible damage occurs to the heart or gastrointestinal tract.