Abundance and Condition of Populations of Small Mammals as Carriers of Natural Focal Human Diseases in the Karelia North-East Ladoga

Summing up the results of the long-term studies of population ecology and dynamics of small mammals for more than half a century (1966–2018). Small mammals are involved in the formation and functioning of natural-focil of human vector-borne diseases common in the North-Eastern Ladoga region. Encephalitis and tularemia circulate intensively in the Ladoga region under conditions of intensive anthropogenic transformation of taiga ecosystems. Local landscapes belong to the subzone of the middle taiga forests. Most of the studied species of small mammals are located in the northern periphery of this area. Here representatives of the native taiga fauna of Micromammalia constantly experience powerful anthropogenic pressure, which leads to a decrease in their abundance and correlation of the species. Of the total amount of 22 species of small mammals collected here, Sorex araneus and Myodes glareolus dominate. Next, the species prevalent (according to the degree of predominant species) in the counts are Microtus agrestis, Sorex minutus and Sorex caecutiens. Other species are relatively rare and appear in smaller numbers. Myodes glareolus has main role in the feeding of ticks and, accordingly, in the circulation of infections in nature, the differentiated contribution of individual intrapopulation groups in maintaining the number of vectors and the activity of pathogens. Shrews are important for the development of the larval stages of the tick. In the research area, were recorded total index of trap catch of abundance of small animals with trap lines from 0.34 to 18.5 individuals per 100 snap traps-nights (average of 7.8 ind.) and with pitfall traps recorded from 2.7 to 25.4 individuals per 10 ditch-nights (average of 14 ind.). This indicates that the studied area has smaller amount of mammals compared to other regions in Southern Europe. Nevertheless, the studies determine a rather tense epidemic situation in the studied area. Population of small mammals of boreal ecosystem steadily affect the mass feeding of carriers of natural focal infections.