Host-parasite relationship of Trypanosoma corvi in Ornithomyia avicularia.

The first description of an electron microscopic study of Trypanosoma corvi in the vector Ornithomyia avicularia is reported. There is a close association between vector and parasite in the midgut, ileum and rectum of the vector. The midgut distribution of parasites is determined by the peritrophic membrane, which confines the early infection to the endoperitrophic space. Parasites escape from the ruptured region of the peritrophic membrane at the pylorus to gain access to the ectoperitrophic space, where intense multiplication occurs. The resulting, smaller epimastigotes attach to the cuticle in the pylorus, ileum and rectum, where they continue multiplying to give rise to mature, short, stumpy trypomastigotes (metacyclics) that are not attached. Attachment to these cuticularly lined regions occurs by the formation of dense, hemidesmosome-like plaques at the extremities of the expanded flagella. A fibrous matrix surrounds the parasites in the ileum. For the first time, intracellular midgut forms are reported for T. corvi in O. avicularia. These parasites enter the cells between the microvilli and penetrate deeply between the folds of the midgut. In the midgut of O. avicularia, the cells of a mycetome region are packed with Rickettsia-like organisms. The significance of these intracellular parasites in the relationship of T. corvi in O. avicularia remains unknown.