Yellowstone cougars infected with Bubonic plague

Cats in West susceptible to age-old disease

Before the COVID-19 pandemic, way back in the 1300s, there was a pestilence known as the “Black Death,” also called bubonic plague.

Estimated to have killed millions during several outbreaks, the bubonic plague is caused by a bacteria known as Yersinia pestis.

Although the new coronavirus pandemic has captured headlines and attention around the world over the past two months, bubonic plague has once again reared its head, this time in the Greater Yellowstone Ecosystem. A recent study showed 4 percent of the 17 cougars that were captured and had their blood drawn in the southern GYE tested positive for exposure to the plague.

This suggests that Y. pestis may be present at higher levels in the GYE than previously assumed, according to the study, and that the disease was also found in four of 11 mountain lions that were necropsied.

The study is not the first time that exposure to Y. pestis has been found in Greater Yellowstone Ecosystem cougars. A 2006 study tested blood from 150 cougars collected over 15 years and found relatively low exposure to the bacteria — less than 20 percent.

The study found Yellowstone cougars in 2004 and 2005 that had succumbed to bubonic plague. When captured in the winter they were infested with fleas. The animals died in the following summer.

“It’s a relatively common bacteria found in wildlife, more so in southern drier areas,” said Dan Stahler, leader of the Yellowstone National Park Cougar Project.

The bacteria is commonly transmitted by fleas that infest rodents, everything from mice to ground squirrels. The cougars, along with other predators like coyotes, are exposed to the virus when they catch and eat infected animals.

However, felines — including bobcats and lynx — seem to be more susceptible to Y. pestis than canines, Stahler said. For some reason bears appear impervious to such infections, he added.

Being aware of contagions is why Stahler and his team approach any dead animal cautiously while conducting wildlife research.

Anyone in contact with animals needs to have such diseases at the forefront of their mind, he said.

“Not to be fearful, or to panic, but it’s important to screen for it and be careful of it,” he said.

In humans, bubonic plague causes enlarged lymph nodes in the armpits, groin and neck. It can also be accompanied by fever and muscle aches, along with other flu-like symptoms. Unlike COVID-19, it can’t be transmitted from an infected person to others via respiratory droplets. Luckily, bubonic plague is also easily treated with a vaccine if caught soon enough.

According to Montana Fish, Wildlife and Parks, detailed data on the distribution of plague in wildlife in Montana is believed to be present throughout the state. The most recent human case of plague in Montana was in 1992 when a hunter contracted the disease from a bobcat. In 1987, a hunter was infected after skinning an infected antelope.

Across the United States only about seven people a year are infected, according to the Centers for Disease Control and Prevention. More prevalent in the Southwest, the United States saw spikes in human infections in 2006 and 2015, according to the CDC.

Ferrets and prairie dogs are another species often infected by bubonic plague. In trying to reintroduce black-footed ferrets across the West, outbreaks of plague have repeatedly frustrated scientists’ efforts. Prairie dogs are the main food source for the ferrets, which also use the rodents’ dens as their living quarters.

The incidence of plague seems to increase in years with cooler summers that follow wet winters, Stahler said, possibly because those conditions are more conducive to flea survival.