[Plague in the modern era, understanding the transmission of Yersinia pestis by fleas].

Plague, caused by the bacterium Yersinia pestis, remains a deadly disease on a global scale. This pathogen is primarily transmitted by fleas, in which it adapts to the hostile environment of the digestive tract, multiplies, and forms a dense biofilm that obstructs the entry of blood. This obstruction promotes bacterial transmission through regurgitation during a blood meal. This process relies on a molecular program initiated in the rodent and sustained within the insect. In this review, we describe the environment in which Y. pestis evolves to infect fleas, as well as the modes of transmission and the molecular mechanisms involved, while adopting a critical perspective to better understand the interactions between Y. pestis and its vector, and to explore new strategies to control the spread of the plague agent.