"Zombie Deer Disease" May Threaten Human Health

By Rae Ellen Bichell | High Country News. This story was originally published at High Country News in collaboration with the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUER in Salt Lake City and KRCC and KUNC in Colorado.

BOULDER, CO – Heather Swanson and Ryan Prioreschi stand in knee-high golden grass on a slope outside Boulder, Colorado, where the Rocky Mountains start slumping into the plains, at the epicenter of a now-international animal epidemic. The two ecologists, who monitor wildlife for the city, have their binoculars out, and they’re staring right at the problem.

Heather Swanson spots the mule deer herd outside Boulder that is known to be infected with chronic wasting disease. A fawn runs circles around the rest of the herd, with the boing of a muscular slinky toy.

“He’s wired,” says Swanson, laughing. “He’s doing laps.”

A few other mule deer rear up on their hind legs and kick each other. Still others just hang out in the shade. It’s a beautiful spring morning and the animals look sleek and healthy. But all is not what it seems. This herd is harboring an infection — chronic wasting disease, or CWD.

Scientists have called this neurodegenerative disease, which attacks deer, elk and moose, a “nightmare” and a “state of emergency.” Lately, the media’s been calling it “zombie deer disease.” Lawmakers are calling it a “crisis” and currently considering at least three bills at the national level to combat it. Researchers, resource managers and others worry it could hurt hunting, alter the landscape, or even jump across species to infect people.

“That is buck number 46,” says Prioreschi, pointing to a deer. “He is positive.” Doe number 22, now lying in the grass, is also positive for chronic wasting disease.“Doesn’t show any symptoms,” he says. “She looks perfectly fine.”

But the mountain lions know that something is wrong. A number of years ago, Swanson and her colleagues studied which deer mountain lions prefer to attack. “The mountain lions were definitely preferentially selecting deer that had chronic wasting disease over those that were negative,” she says. “And for most of the ones that they had killed, we had not detected any chronic wasting disease symptoms yet. So certainly the lions were able to key in on far more subtle cues than we were.”

Unlike us, the lions sense that while a deer might look vigorous and alert, it may actually be a ticking time bomb. That’s one of the many weird things about this disease. It isn’t like viral or bacterial illnesses. The infection can sit in a herd for years, crawling from animal to animal, before people notice anything is wrong.

Then, things can go downhill fast. “Through time (it) degrades, essentially, their brain tissue,” says Swanson. In just a few weeks, buck 46 or doe 22 could start to droop and drool, as an infection gnaws holes into the animal’s brain. “That seems to happen pretty rapidly,” she says. “To our eyes, they look fairly healthy, and within a number of weeks they reach that point — and then they’re gone.”

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