Longitudinal study of Lyme borreliosis in a high risk population in Switzerland.
Zhioua E, Gern L, Aeschlimann A, Sauvain MJ, Van der Linden S, Fahrer H.
Department of Parasitology, University of Neuchatel, Switzerland.
Orienteers from all parts of Switzerland (n = 416) were included in a longitudinal study for Lyme borreliosis. In spring 1986, the seroprevalence was 28.1%. At the beginning of the study, 84.3% of orienteers reported a history of tick bite, and 3.8% reported a past history of Lyme borreliosis. During the first (spring 1986-autumn 1986), second (autumn 1986-spring 1987) and third (spring 1987-autumn 1987) period, rates of seroconversion were 0.6%, 2.7% and 2.1% respectively. During the first and second period, clinical incidence were 1.0% and 0.25% respectively. No active Lyme borreliosis was detected during the third period. Among orienteers who seroconverted during the study (n = 16), only two developed clinical symptoms. Hence, Borrelia burgdorferi infection is often asymptomatic.