Ecological Mechanisms Underlying the Persistence of Yersinia pestis Within an Integrated Model of Natural Plague Focus Stability

Plague remains a significant natural-focal infection, yet the mechanisms underlying the long-term persistence of Yersinia pestis during inter-epizootic periods remain incompletely understood. This study integrated published evidence with epizootiological monitoring data from Kazakhstan (1990–2025) and detailed field and laboratory investigations conducted during 2021–2023 to develop an integrated ecological model of plague focus stability. Abiotic and biotic niches, including soil and burrow substrates, soil biota, free-living amoebae, plants, reservoir hosts, fleas, and adaptive states of Y. pestis, were evaluated. Long-term persistence appears to depend on interconnected ecological niches rather than a single dominant mechanism. Key components include soil and burrow microenvironments, the great gerbil (Rhombomys opimus), flea populations, and stable enzootic cores. Field investigations covered approximately 120,000 km², with 3,058 field samples examined by real-time PCR, of which 34 were positive for Y. pestis DNA. Ectoparasite suspensions showed the highest PCR positivity rate (3.3%). Twenty-four Y. pestis strains belonging to the Medievalis biovar were isolated by bacteriological methods. These findings support the concept of natural plague foci as self-regulating, multilevel ecological systems integrating abiotic niches, reservoir hosts, vectors, and pathogen adaptive states, thereby helping to explain prolonged inter-epizootic persistence and recurrent epizootic activation.