The initial stages of infection of cattle cells with Theileria parva sporozoites in vitro.

Large numbers of Theileria parva sporozoites were separated from Rhipicephalus appendiculatus adult ticks by filtration and were then concentrated by centrifugation. The sporozoites were incubated at 37 degrees C with leucocytes from 6 cattle of Bos indicus and B. taurus types. Giemsa-stained smears and living preparations under interference contrast microscopy were used to follow the course of the infection of the leucocytes with sporozoites. Sporozoites were seen to attach rapidly to about 25% of the leucocytes which they penetrated. After penetration by the sporozoites the morphology of the cells changed to show an increase in cytoplasm and an enlargement of the Golgi apparatus, with which the parasite appeared to become associated. The early intracellular or preschizont stages resembled Babesia parasites. From day 3, the parasite showed the typical morphology of the macroschizont of T. parva. Multiple infections were frequent and up to 8 schizonts were observed arranged around the Golgi apparatus. Multiple infected cells did not survive in culture but some of the cells infected with a single parasite divided to produce 2 infected daughter cells and infected lymphoblastoid cell lines were established in all 21 attempts.