Transovarial transmission of Yersinia pestis in its flea vector, Xenopsylla cheopis.

is the causative agent of bubonic plague, a deadly flea-borne disease responsible for three historic pandemics. Today annual cases of human disease occur worldwide following exposure to . infected fleas that can be found within the rodent population where plague activity cycles between epizootic outbreaks and extended periods of apparent quiescence. Flea transmission of is most efficient in "blocked" fleas that are unable to feed, whereas mammalian transmission to fleas requires a susceptible host with end-stage high titer bacteremia. These facts suggest alternative mechanisms of transmission must exist to support the persistence of between epizootic outbreaks. In this work, we addressed whether vertical transmission could be a mechanism for persistent low-infection across generations of fleas. We demonstrate that infection of the Oriental rat flea, , spreads to the reproductive tissues and is found in eggs produced by infected adult fleas. We further show that vertical transmission of from eggs to adults results in midgut colonization indicating a strong probability that it can reenter the sylvatic plague cycle.