The innate resistance of Kenana cattle to tropical theileriosis (Theileria annulata infection) in the Sudan.

A study was carried out to assess the innate resistance of the indigenous Kenana breed of cattle in the Sudan to tropical theileriosis, Theileria annulata infection of cattle. Nine susceptible Kenana calves were obtained from an area free from tropical theileriosis and the vector tick Hyalomma anatolicum anatolicum and were found negative to T. annulata antibodies in the indirect fluorescent antibody test. They were infected by inoculation of 1.0 mL T. annulata sporozoite stabilate. Three Friesian calves were also infected and served as susceptible controls. The percent of schizont parasitosis (Macroschizont Index, MSI) in the Kenana cattle was reduced by 70% compared to the Friesian calves. The percent of piroplasm parasitemia was also significantly lower in the Kenana calves. The rate of white blood cell reduction was significantly greater in the Friesian calves (P < 0.05). These differences were attributed to the high rate of schizont multiplication in the control cattle. Seventy-eight percent (7/9) of the Kenana cattle recovered spontaneously, and only 22% required treatment compared to 100% mortality in the Friesian controls. These differences were attributed to the high rate of schizont multiplication in the control cattle and, on the other hand, ability of the Kenana cattle to limit the MSI, resulting in less severe damage to the lymphoid tissue during the acute phase of the disease.