Lyme Borreliosis Incidence in Two French Departments: Correlation with Infection of Ixodes ricinus Ticks by

We conducted a prospective study to estimate the Lyme borreliosis incidence in two rural French departments, Meuse and Puy-de-Dôme. Concurrently, we investigated the prevalence of ticks infected with Borrelia burgdor-feri sensu lato (sl) and Anaplasma phagocytophilum. The incidence of Lyme borreliosis decreased from 156 to 109/100,000 inhabitants in Meuse and from 117 to 76/100,000 inhabitants in Puy-de-Dôme in 2004 and 2005, re-spectively, corresponding to a decrease in the density of Ixodes ricinus nymphs infected with B. burgdorferi sl. During the same period, the density of adult ticks increased. Interestingly, B. valaisiana, a nonpathogenic species, infected adult ticks more often than nymphs. These results confirmed the correlation between the Lyme borre-liosis incidence and the density of infected nymphs, a stage preferentially infected with B. afzelii. In contrast, we found a low rate of infection by A. phagocytophilum, ranging from 0 % to 0.4 % in Puy-de-Dôme and from 0.8 % to 1.4 % in Meuse, suggesting a low risk for humans. Key words: Lyme borreliosis incidence—Ixodes ricinus—Ticks— Density—B. burgdorferi sl—France. 50