A deer hunter never expects to see giant warts or tumor-like growths on a white-tailed deer, but they do occur. Over the years I’ve seen many of photos of both live and harvested deer with “tumors,” although I’ve never seen one while in the field. The technical term for these growths is cutaneous fibroma and it’s caused by a virus. From a deer management perspective, there is not much you can do to keep wild deer from getting fibroma.

Cutaneous fibromas (warts) are caused by a naturally occurring virus of the deer’s skin. The virus that causes these unsightly warts in deer is believed to be transmitted through biting insects and/or direct contact with damaged skin. Once the virus enters the skin, warts begin to form. As the warts increase in size, the skin surrounding them is typically hairless and grayish in color. The number of warts on an infected animal can vary from one to several hundred, they can sometimes clump, and can in some cases end up covering much of the deer’s body.

For the most part, these warts will not cause a white-tailed deer any major problems. However, sometimes the growth of the wart can indirectly cause problems by restricting the consumption of food or the deer’s breathing. Although death from fibromas in deer can occur, death from warts is not always imminent it seems. There have been many hunter testimonials of white-tailed deer with warts “shaking them off,” so to speak. I can’t say for sure.

From a deer hunter’s perspective, warts are quite unsightly. Since fibromasts are a virus of the skin, they willl be removed if the deer is skinned. Notice I said IF the deer is skinned. Although the meat of a deer is typically not affected, most hunters that harvest a deer with a large number of warts are hesitant to put the meat in the freezer. This is understandable and probably the safest thing to do. I’ve read some research that found a buck with warts also had internal and cancerous fibromasts.

The take home message today is that warts occur naturally in white-tailed deer populations. Fibromasts can occur on any deer, healthy or otherwise. With that said, they occur rather rarely and there is nothing that can be done from a deer management standpoint. Deer are the only host for the virus, so fear not for yourself should you find yourself standing over an infected animal.

Most hunters that have harvested any number of white-tailed deer have unfortunately found nasal bots. At first glance, what a hunter encounters looks like a large maggot. And it basically is, and they live in the cavities of the nose and mouth. Nasal bots are the larvae of a specific kind of fly that belongs in the genus Cephenemyia. Deer biologists actually find them in a high percentage of whitetail deer, particularly when a thorough examination of the head is conducted. From my experience, white-tailed deer in Texas are much more likely to have nasals bots than not.

These bots are specific to members of the deer family, which also includes elk and mule deer in the United States. Nasal bots begin life when the adult fly lays a group of eggs around the nose or mouth of a deer. The small larvae within these eggs are then released when the deer licks the eggs. The warm, wet saliva creates an environment that permits the “hatching” of the immature bots. These larvae then migrate to the nasal passages and occasionally into the sinuses where they molt into larger stages of the maturing larvae.

The mature larvae then move to the deep cavities in the deer’s mouth called the retropharyngeal pouches. The fully matured bots then exit and pupate in the ground until emerging as adult flies that begin the life cycle all over again.

To a white-tailed deer, for example, these bots are typically only a minor nuisance as they do irritate the lining of the nasal passages and move about in the retropharyngeal pouches. In fact, most sneezing and coughing of deer is assumed to be the result of nasal bots. From a clinical perspective, the bots do not cause deer any harm. No sores, infection, nor other problems have been reported even when the parasites are present in large numbers.

Hunters normally encounter nasal bots after the deer they harvested has begun to cool. After the deer dies, the body temperature falls and the bots begin to leave the nasal passages and oral pouches in search of a more suitable environment. These bots then exit through either the nose or mouth. Bots can also move in the wrong direction, or down the trachea (where it is usually warmer), and may appear to be in the body cavity of the deer even though they are not.

Lastly, nasal bots pose no disease threat to deer hunters and do not harm the venison. Remember, nasal bots are only found in nasal passages and around the mouth of deer. Deer “infected” with these harmless parasites are safe for human consumption, although I suspect many unknowing hunters have discarded carcasses after observing an ugly larvae crawl out of a deer’s nose.

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.”

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.

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.