Good news: “zombie deer” disease (probably) can’t be transmitted to humans

Deer [Credit:]

Over the past several decades, a neurological disease known colloquially as “zombie deer disease” has been spreading across North America. 

Chronic Wasting Disease (CWD) is a fatal, neurodegenerative condition in deer, similar to Mad Cow Disease. Like Mad Cow, it is a prion disease, affecting the brain’s prion proteins, causing the brain to atrophy and become “spongy.” Like mad cow, it can lead to strange movements and tremors. And scientists worry that, like Mad Cow, CWD may be able to infect human beings. 

Deer with Chronic Wasting Disease
This deer shows clear signs of Chronic Wasting Disease. [Credit: Donald Savoy/Wisconsin Department of Natural Resources]
Unfortunately, there is no quick-and-dirty test for prion disease contagion. These diseases can take decades to show symptoms, and testing on humans to see if they can contract the CWD is, of course, both illegal and a very bad idea. So i

nstead, tests have to be carried out over years, using animals as proxies for humans. 

But this year, finally, a study started over a decade ago has published its results, and they are optimistic: macaques who were exposed to brain matter of CWD-infected deer showed no signs of having the disease 13 years later.

Macaques are primates who are often used as substitutes for humans in medical tests, due to our genetic similarity and the fact that they and we tend to get the same diseases. For this study, scientists fed the macaques tainted deer meat and, in some cases, performed surgery to smear infected tissue directly on their brains. Over a decade later, the macaques were euthanized and tested, using “highly sensitive prion disease screening assays,” and no indications of prion disease were found. 

This is a good sign, according to scientists. If the macaques didn’t get CWD from infected deer, then humans probably won’t either.

But of course, that’s a big “probably.” For one thing, we can’t say for sure that humans will react to infected tissue the same way macaques do. For another, this one test doesn’t definitely prove that transmission to macaques isn’t possible, especially since previous tests seem to have shown different results.

So while researchers are hopeful that CWD cannot affect humans, authorities still highly recommended that humans avoid eating meat from CWD-infected deer, or deer who look sickly.

Deer with advanced CWD are generally fairly easy to spot. Symptoms include drooling, weakness, and emaciation — the “wasting” for which the disease is named. However, since symptoms can take time to appear, not all deer with CWD will be obvious, and some meat suppliers have stopped selling wild deer completely. 

Deer with CWD have been documented in 25 US States and two Canadian provinces, Saskatchewan and Alberta.

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