Abstract
Objective of the study was to determine the origin of Y. pestis strains that widely disseminated in natural plague foci of Northern, North-Western Caspian Sea region and Fore-Caucasus in the second half of the XX century. Materials and methods . We have carried out the investigation of properties and whole genome sequencing of 22 Y. pestis strains, isolated between 1923 and 2003 in five natural foci of the souslik type, situated in Northern and North-Western Caspian Sea region and Fore-Caucasus. Phylogenetic analysis was conducted using the data of whole genome SNP-typing, based on 1348 identified SNPs. The search of SNPs in the core genome was performed with the help of Wombac 2.0 software. Phylogenetic relations were analyzed using Maximum Likelihood dendrogram, GTR model. Results and discussion . All the studied strains from the foci of Northern, North-Western Caspian Sea region and Fore-Caucasus fall into phylogenetic branch 2. MED1of medieval biovar. On the basis of whole genome SNP-analysis, existence of two groups of closely related strains, comprising the strains dated 1923-1945 and 1962-2003, has been revealed. The predecessors of the 1962-2003 strains from the Northern, North-Western Caspian Sea region and Fore-Caucasus on the phylogenetic tree are the strains from Northern Aral Sea region that go back to 1945. It testifies to the fact that synchronized activation of a group of natural foci in Caspian Sea lowland and Fore-Caucasus in 1975-1979, after prolonged 20-37 year long breaks, could be caused by the dissemination of the strains from the Northern Aral Sea region. The data of epizootic observations indicate that activation of Volga-Ural sandy plague focus in 1960s preceded the start of registration of plague epizooties in the territory of natural foci of souslik type in Northern, North-Western Caspian sea region and Fore-Caucasus.