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Epidemiology and Pathology

Fig. 4.2 Transmission of Chagas' disease.

Chagas' disease is primarily an infection of children and young adults living in mud huts in rural areas. T cruzi is transmitted by several species of reduviid bugs (especially triatomes) and has been found in some bedbugs and ticks. The most important South American species are Triatoma infestans, Rhodnius prolixus and Panstrongylus megistus (Fig. 4.1). They become infected after feeding on man, an armadillo, or other animal host (Fig. 4.2). There are many local names for the insect, such as kissing bug, assassin bug, Mexican bedbug, cone-nose bug and wild bedbug. Most of these bugs, by preference, bite sleeping children around the face at night. Some species have a painless bite, but others have a powerful salivary toxin which produces intense local pain. The bugs live in cracks in the walls and thatched roofs of rural homes made of mud, adobe, or cane, and also in the burrows of armadillos and the nests of opossums (Fig. 4.3). Reduviids have also been found in stables, in pig sties, and in wood piles within, or adjacent to, houses.

The natural reservoirs of T. cruzi are man and domestic and wild animals. Approximately 150 animals harbor T. cruzi but the most important of these in hyperendemic areas appear to be domestic dogs and cats, and sylvatic opossums and armadillos; skunks, pigs, monkeys, guinea pigs, rats, raccoons and bats also carry the organism. The reduviids become infective within 8-10 days after ingesting trypomastigotes of T. cruzi during a blood meal from one of the animal reservoirs and may remain infective for 2 years. The parasites multiply by binary fission within the digestive tract of the bugs and are transformed first into crithidia or epimastigotes. By the tenth day, these differentiate into infective metacyclic trypomastigotes in the insect's rectum and are passed in its feces. Man becomes infected when the feeding site becomes contaminated by the bug's feces which are loaded with trypomastigotes. Because the bug's bite causes irritation and itching, usually at night when a child or other victim is asleep, the person may rub the contaminated feces into the site of the bite or into the eye. T. cruzi may also penetrate directly through the mucous membranes of the lips or conjunctiva.

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Fig. 4.3 Epidemiology of Chagas' disease. (A) Primitive housing in an area outside Panama City showing thatch roofed adobe and mud huts which are the typical breeding grounds for Chagas' disease. Triatomes or bedbugs (B and C) are found in the burrows of armadillos and the nests of opossums (D) and in the cracks of walls of rural homes made of mud, adobe or cane, where the bugs concentrate near sleeping areas (E). In (C ) the triatome vector is taking a blood meal from a guinea pig. The proboscis is penetrating through the gauze mesh and the abdomen of the bug is greatly swollen by blood that it has ingested during feeding. The opossum in (D) is a Didelphis caught near one of the adobe houses in the upper Maranon River valley of Peru. This animal was naturally infected with T. cruzi, T. rangeli and numerous helminths.

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