Domiciliary reduviid bugs and the epidemiology of Chagas' disease in Panama (Hemiptera: Reduviidae: Triatominae).

Abstract

A continuing field survey of domiciliary reduviid bugs in Central Panama over a 3-year period indicates that Rhodnius pallescens (Barber 1932) is overwhelmingly predominant over other heniatophagous Reduviidae frequenting native houses there. Triatoma dimidiata (Neiva 1914) mentioned prominently in the literature as an important vector of Chagas& disease in Panama, while occurring next in frequency in the house collections, was comparatively rare. Other species were taken so uncommonly that they can be considered as only occasional visitors or accidental invaders in houses. An average of 36.58% of 3283 bugs (virtually all R. pallescens ) taken in house collections contained trypanosomes, 32.71% of the total containing Trypanosoma cruzi (Chagas 1909) in the feces, while from 4.2–8.1% contained the non-pathogenic henioflagellato, Trypanosoma rangeli (Tejera 1921). The infection rate of the 2 sexes of adult bugs with T. cruzi was almost equal, or about 60% in both males and females, while about only 20% of the younger stages were so infected. In an effort to evaluate the potential role of the links in the transmission chain from the infection pool in nature to domesticated bugs living close to the human host, an exploration of peri-domestic and sylvatic ecologic niches was made. R. pallescens was found most frequently in chicken houses and pig pens, although only bugs from the former location contained trypanosomes. Out of a dozen strictly sylvatic sites explored, bugs were found only in trees harboring either animals or animal nests. Opossum nests were the most fruitful, yielding 28 bugs from 6 nests, of which 3 were positive for trypanosomes. Experimental laboratory studies on the defecation time after feeding indicated that R. pallescens , as compared to R. prolixus (Stal 1859) is a tardy defecator. The speculation is made that this delayed defecation may partially account for the apparent inefficiency of R. pallescens as a vector of T. cruzi in Panama. A precursory survey of small terrestrial and arboreal wild animals taken from forests near the native houses revealed that of 209 animals of 8 different species, 41 of 128 opossums examined, or 32.03%, were infected with T. cruzi . None of 43 armadillos examined harbored trypanosomes. Marmosets, anteaters, coatis and sloths were found occasionally infected, but the opossum seems to be the most likely wild vertebrate reservoir.