A nine-year study of cougars in the Yellowstone National Park has found that nearly half of the big cats they tracked were infected with the plague-carrying bacteria Yersinia pestis at some point, according to a paper published last month in Environmental Conservation.
The Y. pestis bacteria is behind the Black Death, the mid-1300s epidemic of bubonic plague that in five years killed over 20 million people in Europe. These days, only about seven people catch Y. pestis each year in the United States. The bacteria lives in the soil, gets picked up by fleas living on rodents, and infects other creatures on its way up the food chain. The new evidence in cougars, also known as pumas and mountain lions, shows how flexible and dangerous the pathogen is in different hosts.