Some preliminary observations on the susceptibility and resistance of different cattle breeds to Theileria parva infection.

Theileria parva-naïve Friesian (Bos taurus), Boran (Bos indicus) and Maasai Zebu steers (B. indicus) were infected with a T. parva sporozoite stabilate dose which had previously been shown to induce an estimated 50% mortality rate in Boran cattle. All the cattle developed patent infections with no significant differences in the length of the prepatent period to development of macroschizonts (P > 0.05) between the three groups. Clinical theileriosis occurred in all eight the Friesians (100%), five out of nine Borans (55.6%) and two out of five Zebus (40%). Three of the Friesians (37.5%), and two of the Borans (22.2%) died of theileriosis. The different cattle types were equally susceptible to the infective dose used as indicated by the length of the prepatent periods, but there was a marked difference in their development of clinical theileriosis. The gradation in resistance to disease confirms the findings of earlier less critical studies and identifies these cattle breeds as suitable for investigations into the mechanisms of resistance to theileriosis.