Excretion of Trypanosoma cruzi by various stages of Rhodnius prolixus

The uptake and excretion of Trypanosoma cruzi by all developmental stages of Rhodnius prolixus were studied. In addition, attempts were made to assess the effects of repeated infections on the excretion of T. cruzi in the excreta of adult bugs (male and female). To estimate the uptake, the size of blood meal on infected animals was measured for each bug and the number of parasites ingested was calculated. The bugs were given subsequent meals on normal animals and parasites were counted in their faeces and urine after each feed. There was no direct correlation between the total number of parasites present in an infected blood meal and the appearance of parasites in the excreta. The initial excretion (faeces) contained most parasites; often in the epimastigote form. On the other hand, later specimens (urine) contained fewer parasites but mostly in the metacyclic trypomastigote form. The number of parasites excreted was initially low but gradually increased in subsequent excretions, especially in female bugs. Male and female bugs showed no appreciable difference in the excretion of T. cruzi in preadult stages while in the adult stage females excreted a significantly higher number of parasites indicating that they were more effective transmitters of T. cruzi than males. All immature bugs, at any stage, which were fed on an infected animal subsequently excreted both epimastigotes and metacyclic trypomastigotes. Some of the adult bugs failed to excrete any forms of the parasites. Finally the excretion of parasites was not appreciably altered by exposing the bugs to repeated infections.