APPENDIX 8

Hosts for T. cruzi

Although triatomines are opportunistic blood feeders, the seven most important vector species (see Appendix 7: Vector species of T. cruzi in the Americas) show a preference for blood meals, with humans being the most desirable, then chickens and pigeons, and dogs and cats to a lesser degree. The nocturnal activity of cats saves them to a degree from these nocturnal predators. Guinea pigs are a delicacy to vinchucas in Bolivia and Peru, where Andeans traditionally raise them inside the kitchen. Guinea pigs have also been a factor for the spread of Chagas’ disease throughout Andean countries. Rats and mice play a lesser role in providing blood meals and a major role as predators of triatomine bugs, as are chickens and cats, thus somewhat suppressing triatomine populations.

An important ecological factor influencing transmission of Chagas’ disease is the association of triatomines with synanthropic animals (WHO 1991). Synanthropic animals are those animals that live around humans. They range from pets, livestock, and rodents to opossums, raccoons, foxes, deer, and other animals that, in part because of deforestation and encroachment upon forests, live close to humans. Because these animals serve as blood sources, they contribute considerably to maintaining or increasing population densities of domiciliary and peridomiciliary vectors. Animals also serve as vehicles to disperse triatomines to other parts of the world. The migratory wood stork (Mycteria americana), as one known example, carried Rhodnius prolixus from the north of South America to Central America and Mexico.

Epidemiologically, sylvatic and synanthropic animals serve as reservoir hosts for Trypanosoma cruzi. (Humans have become the principal hosts.) After Carlos Chagas (1909) found Trypanosoma cruzi in house‑dwelling triatomines, Panstrongylus megistus, he discovered that the two important mammalian hosts in the domestic environment in the transmission cycles were humans and cats. Three years later, Chagas discovered infections in armadillos and recognized Panstrongylus geniculatus as the vector in this purely sylvatic cycle in armadillos. Subsequently, throughout the countries of Latin America, a wide variety of mammals and triatomine vectors have been identified as involved in the transmission cycle of T. cruzi and related flagellates. More than 150 species of wild and domestic mammals have been found to be reservoirs of T. cruzi (see WHO 1991: Annex 4 for list).

Certain animals are better reservoir hosts than others. Dogs, cats, and rodents are the prime reservoir hosts within the peridomestic arena, and opossums (Didelphis species) and armadillos within the sylvatic arena. T. cruzi infections in dogs have been reported from fifteen countries and infections in cats from seven, with great variability in infection rates (from 4.5 percent to 100 percent in dogs and from o.5 percent to 60.9 percent in cats). Dogs are important reservoir hosts due to their close contact with humans during the night, the age‑independent persistence of parasitemia in dogs, and the possibility of congenital or lactogenic infection of dogs, as has been indicated by a study in Argentina. Guinea pigs are bred indoors in Bolivia and Peru, where high rates of infection have been reported (Bolivia, 10.5‑61.1 percent; Peru, 19.2 percent [Gürtler et al. 1990; WHO 1991]).

Other domestic animalscattle, goats, pigs, donkeys, and horseshave rarely been found infected. They are not considered to play an important role as reservoirs because of their low population density, their less‑close contact with humans, and their low rates of parasitemia (WHO 1991:25). Some species, such as goats and certain rats, appear to be able to eliminate the infection. Although they serve as blood meals, chickens, turkeys, ducks, and pigeons are not susceptible to T. cruzi infection (see Appendix 10: Immune Response). This is also true for all other birds as well as reptiles. Chickens are used in laboratories to blood feed sterile vinchucas that are used for xenodiagnosis. Veterinary researchers and animal environmentalists need to assess the considerable impact Chagas’ disease has upon domestic and sylvatic animals.