Laboratory Studies Of Trypanosoma Cruzi Infections

All 5 larval stages and the adults of Rhodnius prolixus and adults of Triatoma infestans, T. protracta , and T. maculata were allowed to engorge once only on laboratory rats with heavy parasitaemias of the BH, Sonya or Y strains of Trypanosoma Cruzi . Fourteen or more days after ingesting the trypanosomes, infection rates for metacyclic forms or crithidia in bug feces were between 78% and 92% for larval R. prolixus , the older larvae being least susceptible, and between 64% and 100% for the adults of the 4 species. Adults of R. prolixus were less susceptible (64–98% positive) than those of the other 3 species (97–100% positive). Many years of inbreeding in the laboratory had not diminished the susceptibility of R. prolixus . There was slightly diminished susceptibility in laboratory inbred T. infestans compared with complete susceptibility (100% positive) to all three strains of T. cruzi in more recent isolates of T. infestans from Argentina, Brazil or Venezuela. Sex of adult bug was not important to infection in any of the bug species. Differences in susceptibility to infection in individual bugs appeared to exist as observed from variable densities of motile flagellates in bug feces, occurrence of negative bugs in certain series, and reversion of some of the positive larvae of R. prolixus to a negative condition by the time they were adults. Negative bugs could be infected, or re-infected, but many of them only after repeated feedings on rats with heavy parasitaemias; the feces of a few bugs persisted negative even after 4 or 5 infecting meals.