Ultrastructural observations on the epimastigote stages of Trypanosoma avium in Simulium rugglesi

Epimastigotes of variable size, shape, and density were observed adjacent to the cuticular lining of the hindgut and rectum of Simulium rugglesi that had fed 5 days previously on Trypanosoma avium infected ducks. The parasites were aligned with their flagellar ends towards the cuticle with which they formed zonal hemidesmosomes. Cytoplasmic components of the epimastigotes included free ribosomes, a well-developed anteriorly and posteriorly directed, branched mitochondrial tube with associated kinetoplast, two types of lipid inclusions, homogeneous electron-dense vesicles, and lysosomelike bodies. Dividing epimastigotes were numerous and often possessed two kinetoplasts and flagella, and four basal bodies. Intranuclear spindle tubules were observed in some dividing nuclei, but were unfortunately poorly preserved.