Disease, Parasites & Virus | Deer Hunting & Management

The Spread of CWD in White-tailed Deer

Serious diseases such as chronic wasting disease (CWD) can be detrimental to whitetail deer management programs with mortalities impacting local deer numbers as well as regional and potentially even statewide deer populations. State agencies around the country have been monitoring CWD in deer herds for many years now, and they know that it is caused by prions, but much about the spread of the disease was unknown until now. Researchers have discovered that deer asymptomatic for the fatal brain condition known as CWD excrete the infectious prions that cause the disease in their feces.

The finding suggests a reasonable explanation for transmission of the disease among white-tailed deer, mule deer, and possibly elk and moose in the environment. While the study reveals that prions are shed in feces of symptomatic deer as well, the discovery that the infected deer shed prions in their feces many months before they show clinical symptoms is the most unsettling. White-tailed deer, mule deer, elk and moose inadvertently consume feces and soil in the course of their daily browsing and grazing.

The prion is an infectious form of the normal prion protein, which has been found in all mammals examined, including humans. The lethal, infectious form induces the normal protein to twist into a malconformation, initiating a disease process that ravages the brain. Prion diseases, seen in cervids, sheep, cows and humans, are also referred to as spongiform encephalopathies. In wid and captive deer, researchers now know that the inadvertant consumption of feces is how the disease is transferred from animal to animal. So what’s the next step?

With this information in hand, the researchers set out to determine whether the animals could develop chronic wasting disease through long-term consumption of contaminated feces. They did so by measuring the amount of prions contained in the feces of orally infected deer up until the time they became symptomatic and then calculated whether prolonged exposure to the concentrations of prions in these feces would be enough to cause the disease.

“Prion levels in feces samples of asymptomatic deer were very low compared to those in the brains of the same deer at the time of death,” says the lead author of the study, Erdem Tamguney, PhD, an assistant professor at the Institute for Neurodegenerative Diseases, based at UCSF. “However, the total number of prions excreted over time was sufficiently high enough to cause disease in other deer.”

The susceptibility of animals to infection, he says, may also be increased by the simultaneous ingestion of clay soil, which is thought to enhance the infectivity of prions, possibly by slowing their clearance from the gastrointestinal tract.

“Our findings suggest that prolonged fecal prion excretion by infected deer provides a plausible explanation for the high level of transmission of chronic wasting disease within deer herds, as well as prion transmission among deer and other cervid species. Our work may also explain transmission of scrapie prions among sheep and goats,” says senior author and Nobel laureate Stanley B. Prusiner, MD, UCSF professor of neurology and director of the UCSF Institute for Neurodegenerative Diseases.

The study did not examine whether CWD could be transmitted to humans via exposure to deer feces. To date, transgenic mouse studies have indicated that chronic wasting disease does not transmit to humans, but scientists remain open to the possibility that it could.

“We can only say that prions of chronic wasting disease have not transmitted to mice genetically engineered to carry the normal, healthy form of human prion protein in earlier studies,” says Prusiner. “That said, we do not know for sure that deer or elk prions cannot be transmitted to humans.”

Chronic Wasting Disease Monitoring Continues

State wildlife departments across the United States have continued with their annual Chronic Wasting Disease (CWD) monitoring in wild deer populations. Although numerous research studies are underway, there is currently no vaccine or other biological method of preventing CWD in a free-ranging deer herd. The only tool wildlife biologists and hunters have is to prevent the spread of CWD to new areas, because once an infected prion is deposited into the environment through either an infected carcass or from a live deer, it can remain viable for a decade or more!

Texas Parks and Wildlife Department (TPWD) wildlife biologists and technicians have continued their annual testing of tissue samples (brain stems) from hunter-harvested and road-killed white-tailed deer during the 2008-09 hunting season. To date, Texas has had no documented case of CWD within the State. Many of the samples collected over the hunting season are being prepared for analysis at the Texas Veterinary Medical Diagnostic Laboratory at Texas A&M University in College Station, Texas.

Although CWD has yet to be found in Texas, three hunter-harvested white-tailed deer in Kansas have tested positive for CWD in recent weeks according to the Kansas Department of Wildlife and Parks (KDWP). In the past few years, numerous cases of CWD have been documented in other states located in the central part of the U.S., including Oklahoma, New Mexico, Colorado, Nebraska, and Wyoming.

CWD is a progressive and fatal disease that results in small holes developing in the brain, giving it a sponge-like appearance under a microscope. Decreased brain function causes white-tailed deer, mule deer, and elk to display neurological symptoms such as depression, a droopy head, staggering, loss of appetite, and a lack of response to human disturbance. The continuing deterioration of the brain leads to other symptoms such as weight loss, drooling, and excessive thirst. If hunting in an area where CWD is known to exist, caution is advised. With that said, no human health risks have been discovered where CWD occurs.

The symptoms of CWD in deer include loss of body weight, stumbling, holding the head at an odd angle, circling, non-responsiveness to people, and pneumonia. Hunters can help protect the health of their local deer herd by taking the following steps to avoid accidentally transmitting CWD to new areas. First, do not transport deer carcasses far from the area where the deer lived, especially from areas where CWD has been detected. Secondly, if a deer carcass is transported, the hunter should make sure that carcass waste is not dumped in a location where other deer can come into contact with it. Carcass waste can also be disposed of by bagging and taking it to a landfill.

Deer Warts or Tumors?

When deer hunters head out into the field they don’t usually think to themselves, “Man, I want to harvest a healthy deer.” But we all do, even though we don’t really think about it. So., what if you harvested a deer with warts? Most hunters would be a little concerned because, after all, warts are not normal on white-tailed deer.

Although injuries and diseases are some things hunters and property owners serious about deer management try to avoid having in their herds, it usually can not be avoided.

These “deer tumors”, which are more accurately wart-like growths, and are formally referred to as cutaneous fibromatosis. The virus that causes such growth on the skin can be transmitted between deer, at least experimentally.

Deer fibroma occurs occasionally in white-tailed deer living in North America. Although the ailment is not common, it not extremely rare either. The cutaneous growths can vary in diameter, but usually vary from about 1/4 inch to 4 inches in size.

These wart-like growths can be found growing by themselves or in clusters, typically on the front-end of an infected deer. The whitetail buck featured in the above photos has warts caused by cutaneous fibroma on the underside of his neck and face.

Although these tumor-looking growths are not believed to directly harm the deer, the presence of these warts could cause additional stress or points for additional injury on an animal.

From a hunting or deer management perspective there is little that can be done once a deer contracts fibroma. In some cases the infection may not even be noticeable, but as in the example above, the warts may be very obvious. The virus has been successfully spread under experimental conditions from deer to deer, but the chances of this happening in wild deer herds is unknown.

Supplemental Feeding and Disease Transmission in White-tailed Deer

Feeding and Disease Transmission

Question: A friend and I are considering starting a supplemental feeding program for the white-tailed deer population on his farm where we hunt. Our goal is to, over time produce larger, healthier bucks and does, as well as attract and holding a larger population of high-quality animals for hunting. I have some concern over supplemental feeding and disease transmission within the deer herd.

We are planning to implement food plots as the main approach to this end, but we are also considering supplemental feeding during the winter, when the does are carrying fawns and the bucks are shedding and preparing for the growth of the coming years antlers.

In my research on supplemental feeds, have I found several articles suggesting that supplemental feeding increases the chances of the transmission of diseases like ‘blue tongue’, which is normally associated with deer using the same watering hole as an infected animal.

I have heard of increased infections and deaths caused by “blue tongue” during droughts, when deer populations are concentrated around fewer waters holes, which increases the probability of coming into contact with infected animals.

I know some of the eastern states have done studies which claim this to be the case for supplemental feeding as well, but has have you heard of supplemental feeding causing such problems? Or has anyone seen the direct problems confirming the results that New Hampshire’s and Maine’s Game and fish claim?

They also mentioned the transmission of the “mad cow-like” disease (chronic wasting disease) is possible between deer fed a supplement is likely. Has anyone heard any thing about this?

Response: Feeding Deer & Spreading Disease

Any time animals are concentrated the chances of disease transmission are increased, regardless of the disease or virus in question. Bluetongue is a non-contagious, insect-borne viral disease of both domestic and wild ruminants, which includes white-tailed deer. Although not contagious, deer will be at an increased risk of infection by carrier insects if they frequent the same areas as infected animals.

Bluetongue virus is endemic to the U.S., but it’s more prevalent in specific areas. As such,if you’ve had a history of blue tongue outbreaks in your area, the chances are good it will happen again. Although cattle and wild ruminants serve as reservoirs for the virus, not all animals will die from the virus.

CWD: Feeding and Disease Transmission

Chronic wasting disease (CWD) is a whole other question. Infectious agents of CWD are neither bacteria nor viruses, but are hypothesized to be prions. Prions are infectious proteins without associated nucleic acids. Research has shown that CWD is very contagious, so deer feeding at a concentrated food source WILL become infected.

However, the location of CWD is fairly well known, so you should know if it is in your area, close to your area, or nowhere around. Contact your state wildlife agency or department of natural resources. In Texas, where I’m located, CWD has not been found despite intensive testing by State wildlife officials.

Research has shown that white-tailed deer, mule deer, and elk will become effected if they come in contact with a CWD infected deer, CWD infected dead deer, or if they enter areas where infected deer or infected deer carcasses have been. Despite the fact that CWD is quite contagious, a few deer still seem to be immune.

One thing to keep in mind: Deer are likely to concentrate somewhere – whether it be a water source, food source, bedding area, or travel corridor. Although providing supplemental food will concentrate deer, I suspect that if a disease or virus is present the pathogen will be passed on regardless of whether or not you provide supplemental feed.

Blue Tongue in White-tailed Deer

Blue tongue is an insect-borne, viral disease primarily of sheep, but it occasionally goats and even white-tailed deer. The disease is non-contagious and is only transmitted by insect vectors, especially during periods of drought. The disease is actually caused by a virus belonging to the family Reoviridae.

Species That Can Be Affected

As mentioned, this is primarily a disease of sheep but other species such as goats, cattle, buffalo, antelope and whitetail deer can be infected. Don’t worry, humans can not be infected.

Distribution of Blue Tongue

The virus is present in the United States, so any area can potentially harbor the virus. However, outbreaks typically occurs repeatedly in areas where it has occurred before and especially during dry conditions.

Key Signs To Look For

Characters of disease include fever, widespread bleeding of the oral and nasal tissue, excessive salivation, and nasal discharge. In acute cases the lips and tongue will become swollen and this swelling may extend below the lower jaw.

Lameness, due to swelling of the cuticle above the hoofs and emaciation, due to reduced feed consumption because of painful inflamed mouths, may also be symptoms of this disease. The “blue tongue” that actually gives the disease its name occurs only in a small number of cases.

How Blue Tongue is Spread

The virus cannot be transmitted between susceptible white-tailed deer without the presence of insect carriers. The incidence and geographical distribution of bluetongue depends on seasonal conditions, the presence of insect vectors, and the availability of the density of deer. The insect carriers, biting midges, prefer warm, moist conditions and are in their greatest numbers and most active after it rains.

Life of the Blue Tongue Virus

Bluetongue virus does not survive outside the insect vectors or susceptible hosts. Deer carcases and products such as meat and hide are not a method of spread. Survival of the virus within a location is dependent on whether the vector can over winter in that area.

Controlling Blue Tongue

Within a wild population of deer, there is not much that can be done. With domestic animals, you can use a combination of quarantine and movement controls to prevent spread and reduce transmission and protect susceptible animals. As with just about every disease, less animals will become infected under lower densities.