Lack of manipulation of Rhodnius prolixus (Hemiptera: Reduviidae) vector competence by Trypanosoma cruzi.

Behavioral implications of Trypanosoma cruzi Chagas infection in Rhodnius prolixus Stål were observed. Feeding and defecation behaviors of infected versus uninfected insects were assessed on an artificial membrane-feeding system and on live guinea pigs. Based on a defecation index, fifth instars were the most efficient vectors, followed by adult females, fourth instars, and adult males. Bugs fasted for longer periods (5-6 mo) took smaller blood meals but defecated significantly earlier than bugs fasted for shorter periods (2-3 mo). Multiple blood feeding, degree of fasting, life stage, T cruzi infection, and gender affected the vector potential of R. prolixus. Our data indicate that T. cruzi and R. prolixus have not coevolved to facilitate the transmission of T. cruzi, which suggests that this parasite-host relationship may be relatively recent.

Parasite polymorphism may serve to enhance fitness in different host environments.

Phenotypic expression of trans-sialidase (TS) by Trypanosoma cruzi (Silvio strain) is restricted to a subpopulation (20-30%) of broad trypomastigotes (TS+ parasites), while the larger subpopulation of slender trypomastigotes lacks TS expression (TS- parasites). Rhodnius prolixus nymphs were infected with fractionated T. cruzi parasite populations (Silvio strain). Bugs ingesting TS- parasites produced significantly higher parasite loads than bugs ingesting either TS+ parasites or unfractionated populations. The addition of 1.0 microg of TS monoclonal antibody (TCN-2)/ml of blood meal to TS+ populations increased parasite populations to levels comparable to those of TS- populations. In contrast, the addition of exogenous TS to TS- parasite blood meals significantly reduced parasite loads to levels comparable to bugs ingesting TS+ parasites. These results suggest that T. cruzi trypomastigote polymorphism may serve to enhance survival in different host environments.