[Current characteristics of natural nidality of tick-borne encephalitis: new or well forgotten?].

A number specialists' opinion as to which the rise in the incidence of tick-borne encephalitis at the turn of the centuries is due to the new features of the epidemiology of this infection and to global climatic changes is analyzed. There are no objective evidence suggesting the ongoing expansion of a natural habitat of the major vectors--taiga (Ixodes persulcatus) and wood (I. ricinis) ticks and the noticeable increase in their size and virus infection rates. The notion of the recent penetration of ticks into the metropolises where natural focuses have emerged and human beings are infected is inconsistent with the multidescribed facts. There is no significant evidence for the expansion of a nosoarea of tickborne encephalitis. The impact of reformed anthropurgic foci and that of the proportion of town-dwellers in the general structure of morbidity on the epidemic situation have been evaluated. The intensity of an epidemic manifestation of natural foci is always determined by two most important parameters: 1) the loimopotential of foci and 2) the intensity of the population's contact with them. The nature of an interaction between these factors, which has caused a rapid surge of morbidity rates and their subsequent long-time reduction, is considered.