Genetic diversity of pathogenic Leptospira spp. in small mammals of the Northwestern Federal District of Russia

Introduction. Leptospirosis is a dangerous zoonotic disease maintained by small mammal reservoirs. Studying the pathogen's genetic diversity in animal populations is crucial for epidemiological surveillance.

Aim — detection and molecular genetic characterization of leptospirosis pathogens in small mammals (rodents, insectivores, bats) in the Northwestern Federal District (NWFD) of Russia to assess their species diversity and potential epidemiological significance.

Materials and methods. From 2023 to 2025, 88 bat urine samples and organ specimens from 773 rodents and insectivores trapped in the Arkhangelsk, Leningrad, and Pskov regions, the Republic of Karelia, and Saint Petersburg were collected. DNA of pathogenic leptospires was detected by real-time PCR. Genotyping of positive samples was performed by Sanger sequencing the secY gene fragment followed by phylogenetic analysis.

Results. Genetic markers of Leptospira spp. were found in 11.4% of bat urine samples and in 2.5% of organ samples from rodents and insectivores. The highest infection rates were noted in Saint Petersburg (3.2%) and the Republic of Karelia (3.0%). Phylogenetic analysis revealed the circulation of three species of pathogenic leptospires: L. kirschneri (the dominant species), L. interrogans and L. borgpetersenii. Genetically distinct variants were found in bats, and one isolate (PV807621) showed only 95% similarity to reference strains of L. interrogans, suggesting the possible discovery of a new bat-adapted genetic variant.

Conclusion. This study is the first to demonstrate that small mammal populations in the NWFD are a reservoir for a wide range of pathogenic leptospires. The detection of potentially novel genetic variants in bats underscores their important role in the maintenance and evolution of Leptospira pathogens and highlights the need to consider this factor in epidemiological risk assessment.