Yellowstone's Cougars Are Testing Positive For The Plague


Tom Hale

Senior Journalist

clockApr 10 2020, 12:20 UTC

The cougar, also known as the puma or mountain lion, is the second-heaviest cat in the New World after the jaguar. Baranov E/Shutterstock

While much of the world is gripped in a battle with a novel infectious disease outbreak, cougars in Yellowstone are dealing with a much older pathogenic enemy: the plague.

After noticing cougars were dying in mysterious circumstances during the winter of 2006, researchers tested 28 cougars (aka mountain lions and pumas) in the greater Yellowstone area for Yersinia pestis, the bacteria responsible for the bubonic plague that swept through Europe in the 14th century. Their results found that nearly half had been exposed to the plague between 2005 and 2014.


As reported in the journal Environmental Conservation last month, the researchers found antibodies to Y. pestis were detected in 47 percent of the tested cougars, indicating that almost half had come into contact with the pathogen. They also found the bacteria itself in four out of the 11 necropsies carried out on deceased cougars. 

The disease could perhaps be even more prevalent in cougars than these results suggest, too. One puma, known as M21, tested negative twice over a 3-year period, then tested positive the following year, before testing negative again 1 year later. 

Don't worry, however: the infection poses no significant threat to humans. 


Y. pestis can be found in soil across the world. They maintain their existence in a cycle involving fleas, rodents, and other animals higher up the food chain. It can also infect humans in a number of forms, causing symptoms including fever, weakness, and headache.

While the bacteria is infamous for killing around 100 million people during the Black Death (1347 – 1353), it’s now easily treated by antibiotics. The World Health Organization estimates that there are now just 1,000 to 2,000 cases each year in the world, so the risk to humans is relatively minimal. The three most endemic countries are the Democratic Republic of Congo, Madagascar, and Peru. In fact, cases of plague are reported in Madagascar almost every year. 

Furthermore, this new research is no reason to fear cougars could spark a new disease outbreak as it appears very unlikely that infected cougars will pass the plague onto humans. Mark Elbroch, lead study researcher and puma program director of big cat conservation organization Panthera, told Live Science: "The average person has essentially zero possibility of contracting plague from a mountain lion. So please, do not read into our results as a reason to fear mountain lions."


With that said, the research does hint that the risk of Y. pestis infecting a human isn’t just a concern for medieval Europe. Back in 2015, a boy scout contracted the plague while camping in Yosemite National Park, but – once again – it’s very unlikely this case was contacted from a cougar. 

  • tag
  • disease,

  • plague,

  • yersinia pestis,

  • yellowstone,

  • puma,

  • mountain lion,

  • cougar