Plague, once known as ‘Black Death’ is caused by the bacterium Yersinia pestis. It spreads via infected fleas through many animal populations, including human. Among its common targets are prairie dogs, a type of burrowing rodent. What was not understood until recently was how the plague returns to decimate new prairie dog towns when there are no survivors to maintain it. In other words, where does the bacteria reside in between epidemics (or epizootics, in the case of animals)? Is it hiding in secondary hosts? In the soil? In puddles of fresh water?
Daniel Salkeld and his colleagues from Stanford and from the University of California Fullerton have found the plague reservoir: a carnivorous mouse called the grasshopper mouse (Onychomys leucogaster). These mice feast on insects, worms, scorpions and yes, dead prairie dogs. In so doing, they give infected fleas time to jump aboard the mice, which can then carry them to new, previously uninfected, prairie dog towns.
This result has implications for many diseases that may reside in rodent-infesting fleas, such as hantavirus, or anthrax. It’s not unusual for epidemics (or epizootics) to wax and wane mysteriously. Now researchers can be on the lookout for mice connecting one site of infection to the next.
Top left: grasshopper mouse (Onychomys leucogaster).
Top right: black-tailed prairie dogs (Cynomys ludovicianus).