Rhodnius pallescens has become increasingly domiciliated, invading houses from its breeding places in palm trees. In Panama, 59 percent of its blood feeds were from humans, followed by preferred feeding on opossums and poultry. Chagas’ disease has been more on the increase in central Panama than in western areas of that country because of the association of R. pallescens with the opossum (Didelphis marsupialis). In western Panama, the principal vector of Chagas’ disease is Triatoma dimidiata.
In the United States, triatomines thus far have not adapted to household ecotopes (Ryckman 1986). Rhodnius prolixus and Triatoma dimidiata are the most important vector species from Mexico to northern South America. In Ecuador, Triatoma dimidiata is the primary domiciliary vector species. Rhodnius prolixus is the main vector in Colombia, French Guiana, Guyana, Suriname, and Venezuela. Triatoma venosa and T. maculata are found in homes in Colombia but have only secondary importance. In Peru, major vectors are Panstrongylus lignarius in the north and T. infestans in the south. P. megistus is found in limited areas in Bolivia and Paraguay. T. sordida covers the eastern part of Bolivia, a broad band in southern Brazil, and areas in Argentina, Paraguay, and Uruguay (WHO 1991).
Several species of triatomines are naturally infected with T. cruzi in Brazil. As in Bolivia, T. infestans is the most important, and it has dispersed northwards, reaching the northeastern states of Pernambuco and Paraba. Second in importance, P. megistus has a wide geographical distribution and high rates of natural infection. It is domiciliary in parts of northeastern and eastern Brazil. In northeastern Brazil, T. brasiliensis is the main vector, with T. sordida and T. pseudomaculata generally replacing the main domiciliary species after fumigation. T. sordida and T. pseudomaculata have low rates of natural infection with T. cruzi.
Percentages of infected triatomines are smaller in countries of Central America than in South America, especially Bolivia and Brazil, where averages are around 50 percent. Table 2 shows the infection rate of triatomine bugs with T. cruzi parasites in Central America.
T. dimidiata and R. prolixus frequently harbor the Chagas’ parasite in Central America. T. dimidiata has a much higher rate of infection than R. prolixus in El Salvador and Nicaragua; but, in Honduras, the rates of infection of both species are similar, 34.7 percent and 32.2 percent, respectively, for R. prolixus and T. dimidiata. In Costa Rica, T. dimidiata is the principal vector, with an infection rate of 30.9 percent; and, in Panama, R. pallescens is the principal vector, with an infection rate of 32.7 percent. Within the Panama Canal zone and the provinces of Panama, Colon, Chiriqui, and Bocas del Toro, percentages of infected R. pallescens ranged from 68.7 to 84.1 percent (Sousa and Johnson 197I). In one house alone, approximately 100,000 triatomines were found.
Table 2 RATES OF T. CRUZI VECTORS IN CENTRAL AMERICA (Cedillos 1987:47) | Countries | Triatomine Sp. | Number | % pos. | Source |
| Costa Rica | T. dimidiata | 3276 | 30.9 | Zeledon et al. 1975. |
| El Salvador | R. prolixus | 2068 | 13.6 | Pefialver et al. 1965. |
| T. dimidiata | 1767 | 30.8 | Pefialver et al. 1965. |
| Guatemala | T. dimidiata | 5747 | 23.4 | Pefialver, Fajardo Aguilar 1953. |
| Honduras | R. prolixus | 3238 | 34.7 | Ponce and Zeledon 1973. |
| T. dimidiata | 791 | 32.2 | Ponce and Zeledon 1973. |
| Nicaragua | R. prolixus | 282 | 9.6 | Urroz 1972. |
| T. dimidiata | 18 | 39.0 | Urroz 1972. |
