From the Black Death to Modern Biosecurity: The Continuing One Health Importance of Yersinia pestis

Yersinia pestis, the bacterium that causes plague, is a highly virulent zoonotic pathogen maintained in complex ecological systems involving wild mammals and their ectoparasites, especially fleas. Plague has caused three recognised pandemics and profoundly influenced demography, commerce, warfare, and public health practice. It remains endemic in natural foci across Africa, Asia, and the Americas. From 2019 to 2026, most cases reported to the World Health Organization occurred in the Democratic Republic of the Congo and Madagascar. People are infected mainly through bites from infected fleas, direct contact with infected animals or tissues, or inhalation of infectious respiratory particles. The principal clinical forms are bubonic, septicaemic, and pneumonic plague. Cats are particularly susceptible and can transmit infection to owners and veterinary personnel, while dogs more often serve as sentinels, mildly affected hosts, or carriers of infected fleas. Rapid clinical progression, high mortality without treatment, the potential for respiratory transmission, and a history of deliberate misuse make Y. pestis a high-consequence biological agent. The organism itself is not prohibited: peaceful research, surveillance, diagnosis, treatment, and vaccine development remain legitimate. International law prohibits its development, production, acquisition, stockpiling, transfer, or use for hostile purposes. This review synthesises evidence on bacterial evolution and virulence, historical pandemics, pathogenesis, human and animal disease, zoonotic transmission, biosecurity, and integrated One Health preparedness. Emerging priorities include genomics-informed surveillance, field-deployable diagnostics, antimicrobial-resistance monitoring, ecological forecasting, improved vaccines, and stronger coordination across medical, veterinary, wildlife, environmental, and security sectors.