A simple method of transmission risk assessment in enzootic foci of Lyme borreliosis.

The proposed method consists in examining individual host-seeking vector ticks of the Ixodes ricinus complex by microscopy for borreliae and evaluating the proportion of ticks with more than 100 borreliae. The investigations were carried out in a deciduous oak forest habitat in South Moravia, Czech Republic, over four years (1991-1994). In May (i.e., at the peak of seasonal activity of I. ricinus), about 150 nymphal and 200 adult ticks were examined each year. It was found that annual incidence of human Lyme borreliosis in the region correlated better with the proportion of heavily infected ticks than with the overall infection rate of the ticks.