Comparison of infectivity of Trypanosoma cruzi blood stream trypomastigotes and metacyclic trypomastigotes from Rhodnius prolixus.

Four strains of Trypanosoma cruzi (Y, BG, M and Peru) retain their ability to infect Rhodnius prolixus and to produce virulent infections in mice for from 12 to 39 years. About 60 or more metacyclic trypomastigotes were consistently lethal to mice. The mean number of metacyclics per bug ranged from 1.2 to 17.3 x 10(3). Comparative studies of virulence of metacyclics and blood trypomastigotes showed the blood forms to be slightly more virulent. The route of injection was shown to be more significant in varying the host response to infection, subcutaneous inoculation being the preferred route.