Zombie Deer Disease: Rising Concerns and Preventive Measures Following First Case in Yellowstone National Park
According to a report by Fox News USA on the 23rd, the first case of “zombie deer” disease was discovered in Yellowstone National Park, causing concern among scientists who warn that the virus could potentially be transmissible to humans.
In November, a dead deer in Yellowstone Park tested positive for a highly contagious prion virus, causing symptoms such as weight loss, stumbling, lethargy, and neurological disorders in deer. This disease is commonly referred to as “zombie deer” disease. The virus has been found in deer populations in North America, Canada, Norway, and South Korea.
The Centers for Disease Control and Prevention (CDC) in the United States describe “zombie deer” disease as a prion-caused “chronic wasting disease” (CWD), affecting animals such as deer, reindeer, roe deer, elk, and moose. So far, there have been no reported cases of human infection.
However, some animal studies indicate that CWD poses a risk to certain types of non-human primates, such as monkeys, who may consume meat from infected animals or come into contact with brain tissue and body fluids of infected deer. These studies have raised concerns about the potential risk of the virus being transmitted to humans.
What is “zombie deer” disease? “Zombie deer” disease, less commonly heard of compared to mad cow disease, is also a prion disease.
The formal name for “zombie deer disease” is “chronic wasting disease” (CWD). It is a contagious spongiform encephalopathy primarily causing central nervous system disorders. Its main pathological features are vacuolation of neurons, spongiform changes in the gray matter of the brain, proliferation of astrocytes, accumulation of the pathogenic PrPSc, and amyloid plaques.
Deer infected with CWD exhibit symptoms like weight loss, incoordination, instability, lethargy, drooping ears, drooling, excessive thirst or frequent urination, fearlessness towards humans, or unprovoked aggression. Once symptoms appear, most deer die within a year, and the incubation period ranges from 16 months to 5 years. Their behavior becomes zombie-like.
Prions are proteins, referred to as viruses but consist only of proteins without nucleic acids. They are self-replicating infectious agents. The replication process involves the prion protein (Sc-type PrP) coming into contact with the normal cellular PrP (C-type), causing the C-type to convert into the Sc-type. Simply put, normal prion proteins (PrPC) in the host undergo misfolding under accidental conditions, transforming from a “good” protein to a “bad” one, specifically an abnormal protein with partial protease resistance.
CWD was first discovered in the United States in the 1960s, primarily infecting North American species like mule deer, white-tailed deer, Rocky Mountain elk, and moose, both in captivity and in the wild. Cases of CWD were reported in South Korea in 2002 and Norway in 2016.
Can “zombie deer” disease be transmitted to humans? The prevalence of CWD in free-ranging deer can be as high as 30%, and in captive herds, it can reach up to 100%. CWD can be transmitted horizontally (through oral ingestion) and vertically. Prions of CWD can be detected in the brains, spinal cords, eyes, peripheral nervous tissues, various lymphatic tissues, skeletal muscles, hearts, bladders, nasal epithelium, and distal intestines of infected animals. The pathogen can be excreted and released from sick or dead animals, contaminating soil, plants, water sources, and all objects contacted by infected deer. Notably, the blood of sick animals and deer antlers can carry the pathogen, and these products are also significant ways humans can come into contact with the pathogen.
No cases of human infection have been discovered so far. However, the possibility of transmission through the food chain after infected deer are preyed upon exists, and Canadian researchers have found that CWD can be transmitted to macaques through the consumption of infected meat, not ruling out the potential for human infection.
How can humans avoid potential transmission? The CDC in the United States advises:
- Do not hunt, handle, or eat deer, elk, or moose that behave oddly or appear sick. Avoid consuming deer found dead on the road.
- Wear rubber or latex gloves when processing game.
- Avoid contact with brain or spinal cord tissues.
- Do not use household knives and kitchenware for game processing.
- Test deer or elk for CWD before consumption and stay informed with announcements from health departments.
- Be cautious with importing deer and deer products from countries or regions where CWD has been found.
