The contribution of woodiniee (Apodemus sylvaticus), yellow-necked mice (Apodemus flavicollis) and bank voles (Clethrionomys glareolus) was compared in a focus of Lyme borreliosis in Switzerland during a 7 months’ study. All three species of mice and one species of shrews (Sorex araneus) were shown parasitized by infected Ixodes ricinus immatures. About 14% of larvae and 50% of nymphs collected on small mammals were infected with B. burgdorferi. Spirochetes were isolated from blood of 3 woodmice and one yellow-necked mouse. The infectious status of rodents was estimated by tick xenodiagnosis. Prevalence of infected rodents ranged from 20% to 44%. Mice presented a higher potential infectivity than voles. The prevalence of infected rodents showed a seasonal variation.
The methods of spatial statistics were applied to assess the geographical pattern of risk of Lyme borreliosis in Central Bohemia, the Czech Republic, based on retrospective data on disease contractions. The statistical risk was then compared at 15 selected localities with the infection challenge presented by ticks and insects carrying borreliae. Over 5,000 Ixodes ricinus (L.) ticks and 390 hacmatophagous dipterans were screened by direct immunofluorescence method, and the spatial and seasonal variance of infection rates were studied. Infected ticks were found at each locality throughout the warm season; in nymphs, sample infection rates ranged from 4.9% to 23.1% with a mean of 14.5% in spring, from 7.7% to 28.7% with a mean of 16.1% in summer, and from 7% to 20.6% with a mean of 13.6% in autumn. The statistical risk was found to correlate well with an average nymphal infection challenge, i.e. I. ricinus nymphal abundance x infection rate, at a given locality. Statistically significant cumulation of insect-history recalling patients into several, generally wetland, areas was ascertained; borreliae were revealed in 0.5% of the dipterans examined.