Severe encephalomyelitis with myelomalacia in two young sheep was associated with an unidentified sporozoan parasite that was passing through a schizogonic cycle in astrocytes. Mature merozoites were 5-7 μm in length, had a conoid, subpellicular micro-tubules, paired organelles and many micronemes. Their morphology is compared with that of Toxoplasma and other related sporozoans. The apparent absence of gametogony suggests that the schizogonic cycle in the central nervous system could be an aberrant dead-end cycle.
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