Borrelia-infection rates in tick and insect vectors accompanying human risk of acquiring Lyme borreliosis in a highly endemic region in Central Europe

The methods of spatial statistics were applied to assess the geographical p attern of risk of Lyme borreliosis in Central Bohemia, the Czech Republic, based on retrospective data on disease contractions. The statistical risk w as then compared at 15 selected localities with the infection challenge pre sented by ticks and insects carrying borreliae. Over 5,000 Ixodes ricinus ( L.) ticks and 390 haematophagous dipterans were screened by direct immunofl uorescence method, and the spatial and seasonal variance of infection rates were studied. Infected ticks were found at each locality throughout the wa rm 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 summ er, and from 7% to 20.6% with a mean of 13.6% in autumn. The statistical ri sk was found to correlate well with an average nymphal infection challenge, i.e. I. ricinus nymphal abundance x infection rate, at a given locality. S tatistically significant cumulation of insect-history recalling patients in to several, generally wetland, areas was ascertained; borreliae were reveal ed in 0.5% of the dipterans examined.