Introduction

Plague control remains a pressing issue to date. Despite mature studies of Yersinia pestis and its carriers, stability of plague epizootics isn’t completely determined. Along with altered virulence population establishment principles, Y. pestis variability and selection mechanisms remain unidentified. Mutagenesis modelling using acids, salts, UV and X-rays cannot be applied to natural processes because its contact with wild strains is either impossible or host-mediated. Meanwhile, the influence of host defenses of the Y. pestis habitat carrier is largely neglected. The discovery of mutagenic effects of oxidants, animal phagocyte effectors, on bacteria, revealed potential Y. pestis mutation induction mechanisms in nature. Y. pestis involves different carriers and vectors into biocenosis, becoming a perfect model to study pathogenicity and variability. Benefits from mature studies of microbial and carrier properties, genome stability that determines genetic similarity, and specific flexibility, facilitating an adaptation to varying ecological conditions. Such flexibility owes to regulatory mechanisms and is manifested phenotypically in Y. pestis population properties. Failure to explain longstanding existence of plague foci, disregard for the agent population virulence, the main carrier’s resistance and pathogenetic features caused some researchers to doubt the very existence of the epizootic process and question the idea of Y. pestis occurrence from saprophytes, as a result of snapshot variability.