Should you be worried about ‘zombie deer’? 

George Mason University researcher Amira Roess discusses deer with chronic wasting disease, nicknamed "zombie deer," and what the risk to humans is. 

Zombies have been found in a northern Maryland state park—zombie deer that is. The sick deer are not after human brains, but they could be harmful to humans who have contact with them. 

We spoke with Amira Roess, professor of global health and epidemiology at George Mason University's College of Public Health, to learn about zombie deer. Roess worked on deer-related illness while she was an epidemic intelligence service officer (i.e., an outbreak investigator) at the Centers for Disease Control. She is one of the principal investigators, along with Taylor M. Anderson of the College of Science on a study funded by the USDA examining the nature of human and deer contact in urban areas, specifically in the Washington, D.C., metropolitan area.

What are zombie deer? 

What is referred to as "zombie deer" are actually deer infected with chronic wasting disease (CWD), which is a prion disease. Deer with CWD can appear very unsteady, stumbling a lot, and are often very thin. They may also show other symptoms related to neurological damage. 

Prions are proteins that cause other proteins to unfold. Some describe them as virus-like proteins. When they infect a person or an animal they cause severe neurological damage. This leads to serious symptoms that get worse over time including unsteadiness, loss of the ability to speak or walk or swallow, and weight loss.  

How worried should people be about getting prion disease? 

Fortunately, the risk of prion disease from deer appears low if humans limit their contact with deer, especially their blood and nervous tissue. But this means that we must be very careful and vigilant. 

Why haven’t we heard of prions before?  

You may not remember hearing the word "prion,” but you might remember hearing about a prion called bovine spongiform encephalopathy (BSE), which was commonly called “mad cow disease” by many. That experience showed the world just how deadly prion diseases can be for humans.  

During the BSE outbreak in England in the 1990s, humans became infected after eating beef products that had come from cattle infected with prions. Infected people lost their ability to walk, talk, and had very agonizing slow deaths that could only be diagnosed after death upon autopsy. That was the largest prion outbreak ever documented. What is very concerning is that in the U.S. when we test deer for chronic wasting disease, we increasingly find it. 

Are you worried about outbreaks? 

I am concerned that it is a matter of time before we find prion disease among people whose only exposure was through direct contact with deer. In the case of BSE, it was hypothesized that many infected individuals had first gotten exposed 10 or more years prior to their deaths. We believe that during those 10 or more years the prion slowly caused damage and went undetected until the damage got so extensive, that symptoms appeared. 

How can we reduce our risk of contracting CWD? 

Deer are wildlife, and as with all wildlife, we need to limit our contact with them. In many parts of the U.S.,  white-tailed deer are becoming habituated or accustomed to humans. They know that we generally don't hurt them, and increasingly we do things like feed them. But remember, deer are not pets—they have not evolved to be in such close contact with humans. They are still wildlife and deserve our respect and distance. 

Do not approach deer and train your pets not to approach them either. If you have children or take care of children, make sure to teach them to be respectful of wildlife and to never approach deer or other wildlife. This is especially important if the animal appears hurt, sick, or disoriented. In that case, call 311 or your local wildlife office immediately to get a professional involved to help the animal. 

Is there a group that is more at risk for chronic wasting disease? 

Deer hunters are at an increased risk because of their close contact with the blood and nervous tissue of deer that they have hunted. Numerous educational resources about how to protect yourself  from the risk of prions and other pathogens when hunting are now available. The best advice is to use personal protective equipment (PPE). If a deer appears sick, do not hunt it. Hunters can access information from their local games departments and in the USDA chronic wasting disease website. 

Are there other animals that carry prions? 

So far there have been reports of prion disease in humans, sheep, goats, cattle, mink, cats, and lemurs, among other mammals. Our knowledge about which other animals can be infected is limited by the fact that we don't have active surveillance for prion disease and most other diseases. What we know is very limited and confined to our experiences with cattle, deer, and other animals that have been found infected because of symptoms. Prions can remain in the environment for long periods of time, and they are very difficult to destroy.  

What can we do to protect deer? 

Remember that all wildlife deserve our respect and deserve to be left alone. Do not feed deer or other wildlife and remove all food sources (such as trash) to protect deer, raccoons, squirrels, birds and other animals.  

When people approach an injured or sick animal, we often cause stress to the animal which then can make the animal sicker. If a deer looks sick, you should exercise extreme caution and not approach it. Instead, call 311 and report the deer so that it can be tested. 

Studies have found that wildlife are losing their fear of humans, and this is linked to an increase in illness in these animals and also in people. Remember that wildlife carry numerous diseases that can harm people, including deer ticks that spread Lyme disease, and raccoons, coyotes, and foxes that spread rabies.

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To speak to Amira Roess about chronic wasting disease, please contact Michelle Thompson at mthomp7@gmu.edu 

Amira Roess is a professor of global health and epidemiology at George Mason University's College of Public Health, Department of Global and Community Health. She is an epidemiologist with expertise in infectious diseases epidemiology, multidisciplinary and multi-species field research and evaluating interventions to reduce the transmission and impact of infectious diseases. Roess currently oversees several longitudinal studies to understand emergence and transmission of zoonotic infectious diseases globally, including the emergence and transmission of Campylobacter (with support from The Bill and Melinda Gates Foundation), MERS-CoV (with support from the US National Science Foundation), and the development of the microbiome during the first year of life. She studies links between food animal production and emerging infectious and zoonotic disease emergence globally, and mHealth (especially apps) technology integration and evaluations to reduce the impact of infectious diseases outbreaks, promote health care and health reduce disparities.   

Some of her deer-related work appears in these journal articles: 

• Novel Deer-Associated Parapoxvirus Infection in Deer Hunters 

• Surveillance of parapoxvirus among ruminants in Virginia and Connecticut 

More resources about chronic wasting disease can be found here: 

• Centers for Disease Control 

• U.S. Department of Agriculture