Seventy-four cattle, from three farms endemic for tropical theileriosis in the north of Tunisia, were studied for tick populations from June 1991 to June 1992. Ticks were removed from cattle twice a month in the summer and every month the rest of the year. They were identified and assessed for Theileria infection. A total of 5083 Hyalomma adult ticks were collected and the major species found was H. detritum (84.3%). The activity of this species is limited between June and August with a peak in numbers observed at the end of June and the beginning of July. Amongst the 2356 Hyalomma ticks dissected, no evidence of salivary gland infection was found in either H. m. marginatum or H. a. excavatum. However, 12.4% (277/2230) of H. d. debitum dissected ticks were infected with Theileria species and amongst these, 62% had one to two sporoblasts in their salivary glands (range 1-91). The prevalence, but not the intensity, of infection was greater in females than in male ticks, and the cases of tropical theileriosis followed the peak of infected females. This suggests that female ticks have a more important role in theileriosis transmission than male ticks, A significantly lower number of adult H. detritum were collected from calves, at their first tick season, than from adult cattle. Finally, this study showed that the infestation level of cattle by H. d. detritum and the prevalence of Theileria-infection in these cattle varied between the three farms studied.
