A strange illness nicknamed “zombie deer disease” has been spreading steadily across North America for decades. Officially called chronic wasting disease (CWD), this fatal neurological disorder affects deer, elk, and moose. As of January 2023, CWD has been detected in 31 U.S. states and four Canadian provinces.
What makes CWD concerning is its similarities to mad cow disease. Both are transmissible spongiform encephalopathies (TSEs)—brain diseases caused by abnormally folded proteins called prions.
CWD prions accumulate in an infected animal’s nervous system, brain, and spinal tissue, killing brain cells. Afflicted deer become emaciated, behave strangely, lose bodily functions, and eventually die.
CWD has also been shown to be capable of infecting macaque monkeys that ate meat from infected deer. This raises worries that the disease could someday evolve to infect humans too. Scientists are ramping up research to learn more about chronic wasting disease and assess if zombie deer disease really poses a threat to human health down the road.
What is Chronic Wasting Disease (CWD)?
Chronic wasting disease is a fatal, neurological illness occurring in North American deer, elk, and moose populations. Also termed zombie deer disease, it causes characteristic symptoms like dramatic weight loss and strange zombie-like behavior in infected animals. CWD is part of the transmissible bovine spongiform encephalopathy or mad cow disease.
CWD is caused by abnormal prion proteins that damage the brain and nerve tissue. These misfolded prions accumulate in the deer’s body over a 2+ year incubation period before signs of infection emerge.
The prions then propagate and multiply, eventually forming plaque-like deposits that kill off nerve cells and leave signature microscopic holes in the brain.
Afflicted deer grow progressively emaciated and begin exhibiting odd behaviors like stumbling, trembling, excessive salivation, and lack of fear of humans. Eventually, they lose bodily functions, collapse, and die. CWD is always fatal—there is no vaccine, treatment, or cure.
Where is Zombie Deer Disease Found?
Since first identified in Colorado in 1967, zombie deer disease has spread inexorably across North America. As of January 2023, CWD has been detected in deer, elk, or moose in 31 U.S. states and four Canadian provinces.
The known geographic distribution continues growing annually and has expanded to 26% of U.S. counties and 37% of Canadian wildlife management units.
The disease is spreading largely through natural deer migrations and the transportation of infected farmed animals. Prions are extremely hardy—they remain infectious for years in soil, plants, food sources, and water.
Direct animal-to-animal contact spreads CWD most efficiently as prions accumulate to high concentrations in infected deer’s saliva, blood, feces, urine, and antler velvet.
Humans have also inadvertently transmitted CWD prions far from their origin by moving live infected animals in the past. Transport bans and mandatory CWD testing protocols for farmed herds have since been implemented. Despite containment efforts, halting the disease’s relentless geographic creep seems unlikely at this point.
Is Zombie Deer Disease a Threat to Humans?
While deer-to-human CWD transmission has never been recorded, several troubling discoveries suggest that should not dismiss the possibility it could adapt to infect humans.
Some research found CWD prions begin evolving and adapting after passage through certain species. The deformed proteins appear capable of “jumping” between different species in a lab setting after serial exposures using white-tailed deer and sheep.
Finally, the strong parallels of CWD with bovine spongiform encephalopathy or mad cow disease ring alarm bells. In humans, mad cow disease causes a fatal brain disorder called variant Creutzfeldt-Jakob disease from eating BSE-tainted beef.
No CWD infections have yet occurred in people but with infected deer numbers approaching 20 million, CDC advises caution. They recommend not eating meat from animals known to be infected with zombie deer disease.
Hunters especially should be vigilant and follow all guidance about safe venison handling/consumption to avoid any CWD exposure risk.
Is There a Zombie Deer Disease Cure or Vaccine?
Unfortunately, there are no vaccines, treatments, or cures for chronic wasting disease. The misfolded prion proteins that cause CWD are extremely difficult to destroy and remain infectious even after procedures that typically kill bacteria and viruses like cooking, radiation, sterilization, and disinfection.
Once CWD becomes established in a deer population, it cannot be eradicated so prevention is the only effective strategy. Containment efforts focus on minimizing the spread between geographic areas and herds.
Best practices like safely incinerating infected carcasses, not moving farmed animals from endemic zones, and managed culling of herds when infection reaches certain thresholds can help slow the spread.
In captive herds, CWD spread is minimized by rigorous surveillance, testing, strict biosecurity protocols, and eliminating exposed or infected animals immediately.
But even intensive efforts cannot stamp it out once present. Wildlife managers and deer researchers remain committed to a better understanding of zombie deer disease and the development of efficacious CWD vaccines or treatments with ongoing investigations worldwide.
How They Evolving to Infect Humans?
Research shows that chronic wasting disease prions evolve to infect other species after repeated exposures. A lab study found that deer prions can transmit disease to other ruminants like sheep.
Monkey studies confirm CWD prions also gather in muscles, indicating the potential for foodborne transmission to people. Though no human cases exist yet, these adaptations implying CWD can eventually jump species barriers should not be ignored given the precedents with mad cow disease.
Conclusion
Chronic wasting disease, AKA zombie deer illness attacking North American cervids, looks poised to blaze an unrelenting path through our woods and wild lands in coming decades.
With no cure or vaccine for infected populations, containment presents massive challenges to already overmatched wildlife and land managers.
Direct threats to human health remain speculative at this point but the possibility can’t be dismissed either. Similar prion brain disorders like mad cow disease and its human variant have taught us these stealthy pathogens can quietly mutate and adapt to infect new hosts. Our continued intrusion into habitats pushing humans and wildlife closer together raises risks too.
The unchecked spread of CWD also threatens the long-term survival of deer, elk, and moose since it inevitably kills them. These iconic species hold integral roles in keeping our ecosystems balanced through browsing, culling vegetation, and serving as prey.
As CWD marches region to region, is a collapse of North American cervid populations inevitable? Or can we yet find ways to defend our precious natural resources against this slow-moving disaster? The stubborn persistence of chronic wasting disease begs difficult questions.
References
- Williams ES, Young S. Chronic wasting disease of captive mule deer: A spongiform encephalopathy. J Wildl Dis. 1980;16:89–98.
https://pubmed.ncbi.nlm.nih.gov/7373730/ - DeVivo MT, Edmunds DR, Kauffman MJ, et al. Endemic chronic wasting disease causes mule deer population decline in Wyoming. PLoS One. 2017;12:e0186512.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5648191/
