‘Zombie Deer Disease’ Documented in Yellowstone for the First Time

The neurological condition, called chronic wasting disease, has a 100 percent fatality rate in the deer, moose and elk it infects

a mule deer
A mule deer carcass in Yellowstone National Park tested positive for the fatal neurological illness known as chronic wasting disease. NPS / Neal Herbert

Yellowstone National Park has confirmed its first documented case of chronic wasting disease in the carcass of a mule deer. Sometimes called “zombie deer disease,” the sickness causes brain degeneration in elk, moose and deer. It is 100 percent fatal with no known vaccine or treatment—currently, biologists have “no effective strategy to eradicate it once established,” per a statement from the park. 

“We anticipated that we were going to get a detection,” John Treanor, a National Park Service wildlife biologist with the Yellowstone Center for Resources, tells Billy Arnold of Jackson Hole Daily. “There were likely positive animals in the park.”

Chronic wasting disease (CWD) was first detected in a captive deer at a Colorado research facility in the late 1960s and found in wild deer in 1981. It has since spread to at least 31 states in the continental United States and has also been reported in Norway, Sweden, Finland, Canada and South Korea. 

Yellowstone estimates about 10 to 15 percent of mule deer near Cody, Wyoming, which migrate into the park during the summer, have chronic wasting disease. Dan Vermillion, former Montana Fish, Wildlife and Parks commissioner, tells Mountain Journal’s Laura Lundquist it was “only a matter of time” before the illness was detected in the park. 

The buck that tested positive for CWD was originally captured near Cody and fitted with a GPS collar in March as part of a population study. When the animal stopped moving for more than six hours in October, biologists received an email alerting them that it may have died, per Jackson Hole Daily. They retrieved the animal’s carcass from the landmass separating the south and southeast parts of Yellowstone Lake.

“It was extremely emaciated, very, very skinny,” Tony Mong, a wildlife biologist based in Cody, tells the publication. “It had not been scavenged on, did not look like it had been predated on. It was pretty obvious that it had succumbed to chronic wasting disease.”

Scientists believe that chronic wasting disease is caused by misfolded proteins called prions. CWD prions accumulate in the brain and other tissues and most likely spread through body fluids, either via direct nose-to-nose contact or through indirect environmental contamination. In late stages of chronic wasting disease, animals may show symptoms such as drooling, droopy ears, lack of coordination, listlessness, emaciation and a lack of fear of humans. But the disease has a long incubation period of about 18 to 24 months, so “the majority of CWD positive animals that are harvested appear completely normal and healthy,” per the Wyoming Game and Fish Department

As of now, researchers have not found any strong evidence that CWD can be passed to humans, and it’s unclear whether people can get infected with CWD prions. The disease has experimentally been shown to infect squirrel monkeys and lab mice that carry some human genes. As a precaution, the Centers for Disease Control and Prevention recommends avoiding consuming meat that has tested positive for CWD and suggests hunters take precautions such as testing deer or elk taken from CWD-infected areas, staying away from animals with noticeable symptoms and using latex gloves when dressing the animal or handling the meat. 

Yellowstone is now planning to increase monitoring for the presence of CWD in other deer, elk and moose in the park and to ramp up the investigation of carcasses and collection of samples for testing, per the statement. Biologists will also update the park’s 2021 Chronic Wasting Disease Surveillance Plan in light of this new case, which it anticipates will be done next year.

“What we learned on a personal level from Covid-19 is it’s hard to control a disease when transmission occurs before symptoms appear,” Paul Cross, a USGS research biologist at the Northern Rocky Mountain Science Center, tells Mountain Journal. “So, this is a challenging question that will take us a long time to empirically answer. But national parks serve an important role in providing places to observe and study how ecosystems function.”

Get the latest stories in your inbox every weekday.