Epidemiology of tropical theileriosis (Theileria annulata infection of cattle) in an endemic region of Tunisia: characterisation of endemicity states.

A serological survey on tropical theileriosis was conducted on a sample of 54 farms in a region within the semi-arid bioclimatic zone of Tunisia. Screening of cattle sera at a dilution of 1/160 using the indirect immunofluorescent antibody test with the schizont antigen of Theileria annulata, revealed the presence of animals with positive sera in 92.15% of the sampled farms. The exposure of calves to infection in the first season was shown to be significantly lower than in older cattle. Three endemic situations were identified based on the serological profiles of herds and the incidence and age distribution of disease cases. Endemic stability was observed in farms showing a sero-prevalence of 100% in cattle of four theileriosis seasons or more and by the incidence of the highest disease levels in cattle at their second and third theileriosis season. High endemic instability was identified on the basis of low sero-prevalence rates and the occurrence of the highest disease incidence in cattle at fourth theileriosis season or more.