Ecological Aspects of the Outbreak of Hemorrhagic Fever with Renal Syndrome in the Territory of the Saratov Region

Hemorrhagic fever with renal syndrome (HFRS) is classifed as a most widely spread natural-focal zoonotic infection in the forest and forest-steppe regions of Russia, taking a leading position by the incidence rate among the population. The Saratov region is enzootic as regards to HFRS, but it is not included in the list of constituent entities characterized by sustainably high morbidity rates. In some years, given favorable ecological conditions, explosive growth in the numbers of the red vole (the main carrier of Hantavirus) is registered, which leads to epidemic complications. In the winter 2018–2019 season, an intensive subniveal breeding of the red vole occurred, which led to an increase in the numbers of the species in the spring. The density of such animals increased, they began to spread widely across the territory. Intensive and extensive epizooties in rodent settlements developed in the natural foci of HFRS. This was especially evident in the territory of the forest park zone “Kumysnaya Polyana,” located in the vicinity of the regional center. The numbers of rodents in ravine and floodplain deciduous forests increased everywhere and amounted to 37.6% in spring and 53.7% in autumn per 100 capture gears, which was 1.6–2 times higher than the average long-term level. The index of dominance of the red vole has also doubled and amounted to 69.5%. In general, the infection rate of rodents increased by 2–3 times in the region. This indicator in the territory of the Saratov forest park was 20.6% in spring and 35.3% in autumn. Against this background, a record outbreak of HFRS was registered in 2019, namely, 109.7 cases per 100 thousand of the population, which was ten times higher than the long-term indicator (7.2). The results of this research should be taken into account when organizing and conducting epizootiological monitoring and preventive measures in the natural foci of HFRS and other zoonotic infections.