The Main Carrier’s Function in the Natural Plague Focus

Each plague foci is characterised by its own enzootic triad: main carrier species, Yersinia pestis’ ecological variant and carrier flea species. Y. pestis is other party dependent, whereas rodent–flea system is self-sufficient and can exist outside the focus. Homeostasis is ensured by fluctuations of the main carrier resistance and Y. pestis population virulence within specific norms. Y. pestis populations are affected by the main carrier species resistance level. The main carrier change leads to Y. pestis population change, with the new virulence norm. Failure to explain some enzootic issues, discounting Y. pestis biology and the role of the main carrier resistance brings researchers to paradoxical conclusions about Y. pestis emergence from saprophytes and persistence in burrows as a critical factor of the focus existence. Parasitic systems regularities with specific development cycles are transferred onto bacteria. Main carrier habitat, Y. pestis virulence, flea’ transmissive ability are crucial within important foci boundaries. Environmental effect depends on geobiocenosis, related to epizootic activity fluctuations and cyclic manifestations. Rodents are most heavily affected by the environment. Influence on fleas is mitigated by the carrier. Rodents act as ambient environment for Y. pestis, thus the impact on the population is intermediated by the carrier organism.