Trypanosoma cruzi in the scent glands of Didelphis marsupialis: the kinetics of colonization

This study examined the dynamics of colonization of Trypanosoma cruzi in th e scent glands of the opossum Didelphis marsupialis following direct inocul ation with 10(5) epimastigotes of isolate G-49 (an opossum-derived strain). One, three, and five days, 1 month, and 1 year after inoculation, scent gl ands were fixed for analysis using brightfield and electron microscopies. O ne day after inoculation the parasites, mainly as epimastigotes, were rando mly distributed into the lumen. From the third day on, the parasites still in the form of epimastigotes tended to concentrate closer to the epithelium . The flagellates reached the definitive distribution pattern on the fifth day, when they formed huge clusters deep into the foveae. In samples collec ted 1 month and 1 year after inoculation, the ratio of epimastigotes:trypom astigotes was 1:1, with epimastigotes predominating near the epithelium and trypomastigotes far from it. Our observations suggest that 1: cruzi grows continuously in the scent glands and does not depend on adhesion to promote metacyclogenesis. Metacyclogenesis far from the epithelium seems to be an important selective advantage to both host and parasite, since it assures t he elimination of the infective forms of the parasite when the host expels the glands' contents, which occurs in frightening situations or at times of stress. The morphological characteristics of infected and noninfected scen t glands using transmission and scanning electron microscopies were also de scribed. (C) 2001 Academic Press.