[Risk of human infection with Ixodes tick-borne relapsing fever in different regional subzones of the Perm region].

Serological and epidemiological surveys covered 2407 persons in 20 populated localities situated in all large geographical and regional subdivisions (subzones) in the Perm Region. Indirect immunofluorescence tests revealed serum immunoglobulins to Borrelia burgdorferi sensu lato. Antibodies in 1:40 or higher dilution were found in nearly 5 to 11% of the dwellers of localities in the subzones of south taiga, coniferous broad-leaved forests, and forest steppe; about 3-7% and 1-6% of them were present in the populations of mountain and middle taigas, respectively. According to the frequency of tick suction and the proportion of an immune interlayer among the population within the Perm Region, four districts were identified by varying risks for infection (epidemic hazard) with Ixodes tick-borne relapsing fever. The populations living in the subzones of south taiga, coniferous, broad-leaved forests, and forest steppe run the greatest risk. An area at average infection risk area corresponds to the south part of a mountain taiga subzone and that at lower risk does to the south part of a middle taiga subzone. There is no possibility of relapsing fever contamination outside the area of Ixodes persulcatus ticks at all. Comparison of their own findings and official statistics has made the authors conclude that there is a great hyperdiagnosis of relapsing fever in the region in question.