FACTORS INFLUENCING THE TRANSMISSION AND INCIDENCE OF TROPICAL THEILERIOSIS (THEILERIA-ANNULATA INFECTION OF CATTLE) IN MOROCCO

A longitudinal epidemiological investigation of tropical theileriosis was carried out in an endemic region of Morocco during the 1991 diseas e season. This involved approximately 220 cross-bred cattle on 15 farm s. Data were collected on the frequency of existing infections, the si ze of the vector tick population and the incidences of new infections and clinical disease, and these were then analysed using statistical m odels. The prevalence of subclinically infected carriers of Theileria annulata, the number of adult Hyalomma detritum, the vector, and the p robability of becoming newly infected with T. annulata increased signi ficantly with the age of cattle, although the age effect on new infect ions may be a result of increased tick numbers on older animals. The p robability of clinical disease in newly infected cattle was not signif icantly influenced by age or by the number of adult ticks, but was sig nificantly positively associated with the cattle population on the far m. The number of H. detritum nymphs counted on cattle in the autumn wa s related significantly to the previous adult tick count on the same a nimal.