Etiological Structure of Leptospira interrogans in Natural Foci of the Baikal Region

Introduction: Studying the functioning of natural foci of leptospirosis, analyzing the structure of pathogens and the species composition of animal carriers are important parts of assessing the current epizootic situation in natural foci, necessary for planning and organizing anti-epidemic measures, including specific prevention of this bacterial disease. Objective: To establish Leptospira interrogans serogroups in natural foci in the Baikal Region. Materials and methods: In 2011–2021, we conducted zoological surveys of the territories of the Irkutsk Region within the borders of 10 administrative districts. In total, 1,255 small mammals of 36 species were caught in their natural habitats in accordance with the guidelines of the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing (Rospotrebnadzor). The animals belonged to five orders, including rodents (Rodentia) – 74.2 %, insectivores (Eulipotyphla) – 24.7 %, hares (Lagomorpha) – 0.6 %, predators (Carnivora) – 0.4 %, and bats (Chiroptera) – 0.2 %. Samples collected from the animals were tested using bacteriology, microscopy, and serology methods. Results: Of all the samples collected, 2.3 % gave a positive test result for Leptospira interrogans. Its main carriers in the Baikal Region were representatives of the order of insectivores: tundra borer (Sorex tundrensis Merriam, 1900) and rodents: housekeeper vole (Alexandromys oeconomus Pallas, 1776), water vole (Arvicola amphibius Linnaeus, 1758), long-tailed ground squirrel (Urocitellus undulatus Pallas, 1779), muskrat (Ondatra zibethicus Linnaeus, 1766), and narrowcrusted vole (Lasiopodomys gregalis Pallas, 1779). The serogroups detected included Icterohaemorrhagiae, Grippotyphosa, Javanica, Australis, Pomona, Sejroe, Autumnalis, with the antibody titers ranging from 1:20 to 1:640. Conclusions: Natural foci of leptospirosis are widespread in the Baikal Region. Compared with the results of studies conducted in the 20th century, the relative number of seropositive animals has increased slightly while the landscape of Leptospira serotypes has undergone changes.