Development of Theileria sergenti schizonts in the lymph node of experimentally infected cattle.

Schizogony of Japanese Theileria sergenti of cattle was studied by light and electron microscopy. Schizonts were detected in the draining lymph node between 4 and 8 days after sporozoite inoculation. Macroschizonts (the phase of nuclear division having invaginations) were formed 6 days after inoculation. Subsequently, microschizonts (the phase of merozoite formation displaying rosette-like appearance) were observed 8 days after inoculation. Multiple infections of a host cell with sporozoites were suggested to occur since different stages of schizonts were simultaneously detected in the same cell. Host cells of schizonts were considerably enlarged by parasitism. However, morphological characteristics of the developmental stages of T. sergenti schizonts resembled those of malignant Theileria species (e.g. T. parva). Schizogony of T. sergenti observed in this study seems to be the primary generation.