[Variations in the occurrence of Borrelia in the tick, Ixodes ricinus (L.) in the Olomouc District].

Examinations of 1,998 ticks Ixodes ricinus in the district of Olomouc revealed 182 cases of borrelia, i.e. in 9.1% ticks. Prevalence in males is 10.7%, in females 12.8% and in nymphs 7.0%. A certain coincidence was observed between mosquito incidence, in particular during the first half of the year, and borrelia prevalence in ticks in the course of the following year, with prevalence variations manifested in tick imagos only. A hypothesis is formulated that mosquitos feeding on larger animals, who are often attacked by nymphs of I. ricinus ticks, can increase the infection rate in the hosts by borrelia transmission and thus participate in the increase of tick imago prevalence during subsequent years.