Temporal risk assessment for lyme borreliosis in Denmark

The prevalence of Borrelia burgdorferi sensu late in Ixodes ricinus nymphs in Denmark was found to be approximately 5%. The mean abundance of infected nymphs varied from 0.3 to 4.4 per 100 m(2) according to site. The seasonal occurrence of infected nymphs in a beech forest coincided with seasonal di stribution of neuroborreliosis cases, In order to establish a working hypot hesis, it was assumed that the availability of habitats and human habitat p references is one of the factors leading to low number of neuroborreliosis cases in the spring. In addition, this paper gives a description of the neu roborreliosis cases in Denmark in the period 1985-97 and offers a possible explanation for the variation in cases. The explanation is based on an asse ssment of tick density, which by comparison with the number of neuroborreli osis cases provides information on the infectivity of ticks. The model sugg ests that high temperatures and low precipitation in the autumn is essentia l for the transmission of B. burgdorferi sensu late to reservoir hosts or d evelopment of B. burgdorferi sensu late within ticks, which secures high ti ck infectivity in the following season.