This article originally appeared on The Conversation.
Chronic wasting disease (CWD), a fatal neurological infectious disease that can affect deer, elk, and moose is rapidly spreading throughout North America. CWD was most recently discovered in North Carolina, March 2022. It has been confirmed in thirty U.S. states, four Canadian provinces and South Korea. Dr. Allan Houston is a professor of forest and wildlife ecology in the University of Tennessee's 18,400-acre Ames AgResearch and Education Center. He explains what we know about CWD and what wildlife scientists are working to discover.
Chronic wasting disease can be contagious and is relentless. There is no cure or way to test animals for chronic wasting disease. Once they are introduced to wild populations, there is no real way to stop their spread.
A deer infected with the disease will typically live for between 18 and 2 years. They will not show symptoms for a while, as they go through a lengthy incubation period. However, as the disease progresses, animals will become listless and begin to lose weight.
They can become aimless, oblivious of danger and even emaciated in the last six weeks. They may stand with their legs spread out like sawhorses to keep from falling over.
These "zombie Deer" are often the focus of media attention. However, as the disease progresses in wild, deer become more vulnerable to other diseases, less capable to protect themselves, more susceptible to predation, and more likely to be struck by cars. They are rarely able to live for long enough to become zombies.
In the mid-1960s, a group of deer from Colorado started to show symptoms that could be described as "wasting away." The condition was first discovered when deer were penned. Beth Williams, a wildlife veterinarian, performed necropsies on animals that had been affected by a similar disease. She found brain lesions consistent with transmissible spongiform encephalopathies-diseases of the nervous system that afflict both animals and humans.
Williams and Stuart Young, a neuropathologist, co-authored the first scientific paper to describe chronic wasting disease (also known as TSE) in 1978. The underlying cause of chronic wasting disease remained a mystery.
Stanley Prusiner, a neurologist, discovered that TSE diseases could be caused by a small protein that can become misshaped and resist the body's ability. It got into cells and tricked them into reproducing it. Then, it moved into the lymph system and nervous system. It eventually moved to the brain where it formed small clumps and caused TSE. Prusiner called this nonliving, infectious protein "prion".
Although prion diseases can be fatal, they do not all affect the same species. CWD is a prion that favors deerlike or cervid animals. Other prions can cause human diseases such as Creutzfeldt-Jakob disease. This malady progresses in a similar way to accelerated Alzheimer’s.
Bovine spongiform, also known as "mad Cow Disease", is a prion infection that affects cattle. A small percentage of people who have been exposed to BSE have contracted Creutzfeldt-Jakob disease.
CWD has never been reported in humans. However, laboratory tests have shown that CWD prions can be transmitted to other mammals through several experiments. The Centers for Disease Control and Prevention advise against eating meat from infected animals. Many infectious disease experts claim that while the CWD risk to humans is low it is not negligible. Therefore, risk assessments should consider the possibility of the emergence new strains.
CWD is an example of this. While no one knows where or how it originated, some researchers believe that a mutated virus in prions escaped the species barrier and became deer from animals infected by scrapie.
CWD prions can remain for many years if they are left on the ground in urine or feces. Deer with chronic wasting disease have been removed from their pens for many years. However, the same deer that were placed in the soil contaminated by chronic wasting disease became infected.
Wild herds spread the prion as deer, who are social animals and groom and lick each other. The fall mating season is when bucks look for mates, fight, and breed. They also frequent scrapes where they lick soil and overhead branches left by other deer. These behaviors are responsible for buck's having CWD twice as often as does.
Infected animals can breed for up to a season because the disease doesn't kill them quickly. There is therefore no genetic selection pressure that favors the development of immunity. Recent research has shown that infected animals can sometimes transmit the virus to their offspring before they are born.
CWD can be found in some areas where the infection rate is only 1% to 5%. The disease's impact on herds may not be obvious to hunters, as well. The infection rate may reach as high as 50% or even 100% in other areas. These cases will result in a shrinking and/or younger herd.
Nobody wants to have a disease named for them. Infected deer can often appear healthy even close to the point of harvest. Therefore, it is important to have your animal tested for disease, which is usually done using lymph nodes.
It can take several weeks for the results to be received as CWD spreads. This makes meat processing more difficult.
It is important to understand that once one deer has been infected, it can ignite a firestorm. The disease can be spread by moving dead or alive deer around.
Transferring deer from breeding farms to breed has been linked with CWD's introduction. Elk and moose can spread CWD, regardless of whether they follow state wildlife regulations. Salt licks and baiting stations can increase the likelihood of infection by concentrating deer and creating an area-source buildup.
Groups Urge Phaseout of Elk Feedgrounds to Prevent Chronic Wasting Disease https://t.co/U7ukm4aHDz pic.twitter.com/CTg3DO2BQA
CWD was discovered in my area of work in 2019 in western Tennessee and northern Mississippi. CWD was detected in northern Mississippi and western Tennessee, where I work in 2019. It had a high infection rate at the time. This suggests that it was likely to have been present for many years and was rapidly spreading. About 40% of Ames' herd are infected at the moment.
CWD research has been ongoing in the United States for many decades. It is now in the South. Ames is collaborating with scientists from all over the country to analyze soil and twig samples in order to determine prion concentrations. We also quantify deer visits to scrape sites or salt stations. To prevent further exposure, we are investigating how to destroy salt stations.
We are also studying how dogs detect the disease metabolites and creating an early warning system to prevent it from spreading. This will allow us to compare hunting success after and before a herd becomes infected. Hunting is a passion for the outdoors, and they are the first to stop CWD spreading. Hunting is the main tool for managing deer populations, particularly those with high levels of CWD.
Deer hunters often take samples from the deer they hunt and participate in all stages of research. One hunter stated, "We have brought in everything but the tracks." We hope to scale up our efforts with other scientists as well as provide insight into chronic wasting diseases for animals and humans alike.
Allan Houston is an Associate Professor of Forest and Wildlife Ecology, University of Tennessee. Disclosure: The University of Tennessee, Mississippi State University and Colorado State University collaborate on research on chronic wasting disease at Ames Station.