A Plague of Fleas—Survival and Transmission of Yersinia pestis

T he gram-negative bacterium Yersinia pestis, which undergoes an obligate flea-rodent-flea life cycle, causes bubonic plague, a rapid and highly fatal zoonotic disease that was responsible for at least three pandemics (in the 5–6th centuries, the 8–14th centuries, and the 19–21st centuries). During the mid-1940s, researchers began studying a series of Y. pestis virulence determinants to learn how this pathogen causes disease in its mammalian hosts. More recently over the past decade, researchers have renewed an interest in this pathogen’s interactions with its flea vector, seeking factors that enable the bacteria to persist in these insects. This revived interest in plague-flea interactions helped lead researchers to identify two bacterial factors, called hemin storage phenotype (Hms) and Yersinia murine toxin (Ymt), that are important in maintaining the vector cycle of Y. pestis. Although much remains uncertain about these factors, ongoing efforts to identify and characterize flea survival and transmission factors eventually will illuminate fleaplague interactions that are proving nearly as complex as plague-mammalian host interactions.