Chronic Wasting Disease

There have been notable instances here in Pennsylvania not far from where I live in Clearfield County of chronic wasting disease in deer. CWD is a mad cow-like infectious disease that can turn the brains of deer, elk, and moose into “Swiss cheese” and has been reported in at least 24 states and other countries. Experts are now warning that it could eventually make its way into humans.

This fatal progressive neuro-degenerative illness was first identified in the 1960s. Like mad cow, the disease is spread by prions, the zombie-like pathogenic proteins that aren’t alive and can’t be killed. When they infect an animal, they eat away at its brain, causing a cascade of symptoms that resemble dementia and eventually lead to death. While the disease is still relatively rare, researchers believe it is more widespread than suspected.

“What we’ve seen over the last few decades is that it’s slowly spreading in wild deer populations,” said Peter Larsen, an assistant professor in veterinary sciences at the University of Minnesota who has been studying the pathogen. It’s also spreading among captive deer, elk, and reindeer, which are transported around the country and overseas to hunting ranches, petting zoos, and Christmas-themed farms. That’s how the disease ended up in South Korea, Larsen said. (It’s been identified in Canada and Norway, too.)

When new outbreaks start, they are virtually impossible to contain because, unlike viruses and bacteria, prions can’t be killed. There’s also no good way to find them. So we’re talking about an indestructible, killer pathogen that could be lurking anywhere.

Researchers have long wondered whether the disease, like mad cow, can make the leap into humans. (Mad cow in people is known as Variant Creutzfeldt-Jakob disease.) Late last summer, we got a preliminary and frightening answer. In a paper published in the journal Emerging Infectious Diseases, researchers from Scotland and Canada showed via an experiment in a petri dish that prions from sick animals can indeed infect human cells.

Since then, there’s been no direct evidence of human disease, even in people who ate meat that later tested positive for the pathogenic prions. Still, the experimental research spurred Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, to compare chronic wasting disease to mad cow recently.

Osterholm, it turns out, also warned the British government of the risks of mad cow before hundreds of people were infected in the UK and around the world in the late 1990s. Sitting before a state committee in Minnesota on February 7, he called the chances of humans becoming infected with chronic wasting disease “probable” and “possible,” adding: “The number of human cases will be substantial and not isolated events.” “We don’t want to find out 10 years from now,” Osterholm told Vox, “that we should have been doing something in 2019 but didn’t.”

According to Larsen, it’s not time to freak out, but he warned that this is a growing public health threat. People should not consume infected meat, he said, while also noting there’s actually no good way to know if meat is infected. “There is currently no way for people to rapidly test for prions in meat, on meat processing surfaces, or in live deer,” he said.

The disease is caused by prions, which are not viruses or bacteria. Prions are almost indestructible pathogenic proteins that trigger cells, particularly in the brain and spinal cord, to fold abnormally and start clumping. When that happens, the infected animals begin to develop an array of awful symptoms — dementia, hallucinations, and difficulty walking and eating. The animals eventually become wobbly and disoriented. Those symptoms worsen over time, and since there’s no cure, they always lead to death.

The disease got its name because when prions overtake an animal, it begins losing weight and wasting away. The prions “turn the brain into Swiss cheese,” Larsen said. “I have only seen one deer that has died of [chronic wasting disease] and it was emaciated,” he said. “There are no zombie-like symptoms. Instead, the symptoms are what you would expect to see of a very sick animal: thin, weak, and unable to function normally. It is important to remember that [this] is a neuro-degenerative disease — not a Hollywood zombie disease.”

How does it spread in animals? An animal with chronic wasting disease can spread prions to other animals through direct or indirect contact with bodily fluids such as feces, saliva, blood, or urine. That means that the disease can spread if an infected deer is wounded, for example, and its blood touches an uninfected animal; or if a healthy animal comes into contact with soil, food, or water that’s been contaminated by a sick deer.

That’s not all, Larsen said. Because prions are so robust, they can survive in environments — farms, forests — for years, decades even. “So let’s say you have a deer with chronic wasting disease, and it started shedding [prions] in its urine, feces, saliva.” If that deer dies on the forest floor, the prions can survive and bind to soil, where plants soak them up. Those plants can then spread prions through their leaves, Larsen said. “So it’s spreading in the wild, slowly. And every year, we see more and more cases of chronic wasting disease.”

How would it spread to people? There have been no documented cases of chronic wasting disease in people, but researchers think it’s possible and becoming more likely, as infections become more prevalent in animals. So far, the only evidence scientists have of spread beyond hoofed mammals, like deer, is indirect. In lab experiments, scientists have shown that the disease can spread in squirrel monkeys and mice that carry human genes, the Centers for Disease Control and Prevention says. In a yet-to-be-published study, macaques — a primate species that’s genetically similar to humans — that were fed infected meat contracted the disease.