Babesia divergens in France: descriptive and analytical epidemiology.

Babesia divergens cause of bovine babesiosis transmitted by Ixodes ricinus, is widely spread especially in West, Central and South-West parts of France. It occurs with two annual peaks, in spring and autumn. The study was carried out during a period of two years (1991-1993) in four farms in the Sarthe area, in order to know the distribution and the ecology of I. ricinus, and to show the presence of B. divergens. Cattle are parasitised as early as March essentially by adult ticks, according to a seasonal distribution (spring, autumn). The flag method allows to catch essentially the larvae and the nymphs on the pastures; nymphs appear as early as March, and larvae one to two months later. Ectoparasite collection on trapped micromammals (Apodemus sylvaticus, Clethrionomys glareolus, etc.) in pastures hedges, is used to detect small I. ricinus populations, mostly larvae. A new ELISA method has been used for the study of the kinetics of anti-B. divergens antibodies in 236 cattle during two years. Most of the animals (60%) show a high antibody level, essentially at the end of the pasture season; the percentage of positive animals decreases during winter and increases again during the pasture season. Calves become seropositive since their first months on pastures. Adults show asymptomatic infections several times along the year, mostly during spring and autumn; only three clinical babesiosis cases have been observed during the whole study, in animals exhibiting nevertheless a high specific antibody level.