Using large selections the unified system of landscape districting of HFRS natural foci with allocation of special geo-botanical provinces has been developed. This permits to avoid various deviations were found to appear during association of epizootiological and epidemiological indexes of separate towns and rural districts when estimating regional parameters. Adequacy of the offered system in confirmed by five-fold increase of the correlation between HFRS epizootiological parameters and antibody prevalence rate in humans. The steady maximum of all parameters was registered in the province situated in broad-leafed oak-line forests. Minimal values are found to correspond to one located in forest-steppe (with birch and asp forests) which poor fodder potential for rodents is well known. Other provinces between these ones are characterized by consecutive decrease of all index values according to the landscape type. According to estimated natural activity rate all the provinces are divided to three groups. The first one (antibody prevalence rate is above 5%) unites the high activity HFRS natural foci. Their common geographical location is on the territories with highest rodent population rates. The second group (antibody prevalence rate--2-4%) includes HFRS foci with average activity, and the third one (antibody prevalence rate is below 2%)--with low activity. The most of the last group provinces are situated on periphery or behind the bank vole living area.

Lungs of 9127 small mammals of 17 species trapped in Khabarovsk region, Magadan, Amur, and Sakhalin regions in 1982-1987 were examined, among them 11 species are reservoirs of HFRS virus. Most frequently infected are striped field mice and Japanese field mice, red voles and large-toothed red-backed voles which are the dominant species of the appropriate landscape formations. Circulation of two HFRS virus serotypes among small mammals was demonstrated. The main epidemiological role belongs to the striped field mouse in HFRS foci of the meadow-field type, and to Asiatic field mouse in forest foci in the territories examined.

For the first time in the study of epizootology of hemorrhagic fever with the renal syndrome (HFRS) in wild animals data are presented indicating certain relationship between true infection rate of bank voles with HFRS virus and the content of the circulating antigen of HFRS virus and antibody to this virus in these animals. Different age groups of animal populations were shown to have different intensity of immunity: it was more marked in animals of older age groups, and less in young animals. On the contrary, live virus was most frequently found in young animals. It has been shown that for successful isolation of the virus from bank voles it is necessary to take into consideration the characteristics of acute infection in rodents: the presence of HFRS virus antigen in their lung tissue and the lack of antibody to the virus in the blood.