For the first time natural leptospirosis focus was revealed in the Irkutsk suburb in 2012 - 2014 during epizootological inspection of a pond-marsh complex. Total 74 small animals (14 species) were examined, specific fragments of Leptospira DNA were found in 16,2%; positive in microagglutination test results were in 1,6% of the samples. Two pathogenic Leptospira strains were isolated from tundra common shrews (Sorex tundrensis) and one isolate - from a water vole (Arvicola terrestris). Circulation of pathogenic Leptospira in a city line represents a potential risk of infection for local population that requires the planning and realization of appropriate preventive actions.

Background. In presence the epizootiological situation on leptospirosis in the territories adjacent to Lake Baikal is not studied well. The showing up of natural focus, discovering of host animal’s species composition and etiological structure of leptospirosis causative agents are essential to plan any epidemiological response and to organize the specific prophylaxis.Aim: to analyze contemporary characteristics of leptospirosis natural foci at the territories adjacent to Lake Baikal.Materials and methods. From 2011 till 2020 the territory of nine Irkutsk Region's administrative districts was investigated. Trapping has been done at four kind of sites (wetland, meadow, forest-shrub, steppificated meadow) and boroughs. 1152 small mammals which belonged to 35 species were collected. Collected samples were studied by complex of methods. Serogroup belonging was detected by micro agglutination and decomposition test, and genomic species – by Microflex LT mass analyzer.Results. A leptospirosis natural foci in the Irkutsk city boundary was newly founded and there were isolated (from small mammals) four pathogenic cultures of leptospiras belonging to Javanica serogroup. Main hosts of causative agents at the territories adjacent to Lake Baikal were defined (insect-eating mammals: tundra shrew, largetoothed Siberian shrew, even-toothed shrew, shrew-mouse, and rodents: root vole, ground vole, narrow-skulled vole, sewer rat). By micro agglutination were defined pathogenic leptospirosis serogroups (Icterohaemorrhagiae, Grippotyphosa, Javanica, Pomona, Sejroe, Autumnalis, Australis), all over 2.4 ± 0.45 % seropositive. Antibody dilution at survey animals ranged from 1 : 20 to 1 : 640. On the grounds of PCR results the mean value of infected animals in studied sample was 16.4 ± 1.14 %. Positive PCR findings were at 19 from 35 animal species.Conclusion. At the territories adjacent to Lake Baikal In the Baikal region, the proportion of animals that have had contact with pathogenic leptospira is quite high. Natural focus of this infection are highly pervasive in this region, they are evolved mainly in dewy sites.