Emergence, global dispersal, and local adaptations of Yersinia pestis , the agent of plague

Yersinia pestis, the causative agent of plague, is a zoonotic bacterium that split at least 6,000 years ago from Yersinia pseudotuberculosis through plasmid acquisition, gene loss, and point mutations. These genetic events enabled a shift from the fecal-oral route to vector-borne transmission and facilitated systemic spread. In the course of its evolutionary history, Y. pestis has caused an unaccountable number of human outbreaks, at both regional and pandemic scales, of which three global pandemics have been documented from historical sources. The bacterium currently persists in sylvatic (enzootic) natural foci across Africa, Asia, and the Americas. Its persistence depends on the co-occurrence of reservoir hosts (mainly mammals) and competent vectors, primarily mammal ectoparasites, and their occurrence is shaped by environmental conditions. However, ecological variation among foci and limited epidemiological data still hinder our understanding of plague dynamics. This review examines the genetic evolution of Y. pestis, traces the bacterium's history, including its global spread, and presents the main actors of sylvatic plague involved in the bacterium's maintenance, with a special emphasis on the knowledge of vectors and hosts in countries that have reported cases of plague over the past decade. The global dispersal of Y. pestis has led to its adaptation to several distinct environments, highlighting the need for a comprehensive surveillance strategy for a better understanding of the ecological drivers of Y. pestis persistence and transmission within each of the geographical regions it is maintained in the natural environment.