Ultrastructure of Tachyzoites, Bradyzoites and Tissue Cysts of Neospora caninum

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Abstract
Dividing tachyzoites of Neospora caninum were 4 .times. 3 .mu.m and had ultrastructural characteristics typical for the cyst forming coccidia. Unusual ultrastructural characteristics of fully-formed tachyzoites included no micropores, 8-12 anterior and 4-6 posterior rhoptries, and a few posterior micronemes. Most tachyzoites were located free in the host cell cytoplasm; only a few occurred within a parasitophorous vacuole. Parasite multiplication appeared to be rapid because most organisms were in various stages of endodyogeny. Neural tissue cysts of N. caninum were 24.3 .times. 19.2 .mu.m and contained 50-200 bradyzoites (7.3 .times. 1.5 .mu.m), which lacked micropores. The cyst wall was 0.74-1.12 .mu.m thick and consisted of the primary cyst wall (the parasitophorous vacuole membrane) and a thick granular layer with electron-dense vesicles.