Transmission of Flea-Borne Zoonotic Agents^*

Flea-borne zoonoses such as plague (Yersinia pestis) and murine typhus (Rickettsia typhi) caused significant numbers of human cases in the past and remain a public health concern. Other flea-borne human pathogens have emerged recently (e.g., Bartonella henselae, Rickettsia felis), and their mechanisms of transmission and impact on human health are not fully understood. Our review focuses on the ecology and epidemiology of the flea-borne bacterial zoonoses mentioned above with an emphasis on recent advancements in our understanding of how these organisms are transmitted by fleas, maintained in zoonotic cycles, and transmitted to humans. Emphasis is given to plague because of the considerable number of studies generated during the first decade of the twenty-first century that arose, in part, because of renewed interest in potential agents of bioterrorism, including Y. pestis.