The Geography of Natural-Infection Foci of Tick-Borne Encephalitis in the Territory of the USSR

A map of the habitat of tick-borne encephalitis is compared with maps of distribution of various physical-geographic elements to determine significant factors in the formation of natural-infection foci of tick-borne encephalitis. Key factors are found to be a stable climate with annual sums of temperatures close to 2000° C., a dissected terrain, high-grade forest stands with a rich grassy ground vegetation, which supports the domesticated or wild mammals that serve as hosts of adult ticks, and landscapes in which the original forest cover is being re-established after overgrazing or overcutting. Provinces of distribution of infection foci are distinguished in terms of these factors.