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Contact information
For information on wildlife health, contact:
Nancy Businga
Wildlife disease specialist/health lab manager
Bureau of Wildlife Management

Health issues for Wisconsin deer

Monitoring the health of the Wisconsin deer herd is conducted year round. In cooperation with hunters, annual health testing is done on deer harvested in the fall hunt. Sick and dead deer reported to DNR wildlife managers are also examined for disease throughout the year.

You can help keep the deer herd stay healthy. Early detection is the best defense we have in controlling these infectious diseases. If you see a deer with any of the disease signs described here, signs of CWD or if you see several or more dead deer in one area, contact your local DNR office. For a county map of local staff contacts please view the sick deer guidance.

Corn toxicity

Deer stomach full of corn

Deer found dead in Wisconsin suspected of dying from corn toxicity.

Corn toxicity is in reference to two diseases which can affect ruminants, including white-tailed deer and elk. Both diseases can cause mortality in any ruminant even those in good body condition and include acidosis (grain overload) and enterotoxemia (overeating disease). While these diseases can occur at any time of the year they are usually seen in late winter when there is a rapid change from a natural diet of high fiber woody browse to a low fiber/high carbohydrate diet found in grain such as corn.

In acidosis the ingestion of large amounts of grain, usually corn, results in a change in the microbial organisms within the rumen which leads to the production of large amounts of lactic acid. The lactic acid lowers the pH of the rumen which then further reduces the normal flora of the rumen leading to reduced rumen motility and interference with digestion.

In enterotoxemia the ingestion of large amounts of grain, usually corn, results in an overgrowth of the bacteria Clostridrium perfringens. This overgrowth leads to the production of lethal amounts of toxins which are absorbed into the animal's body.

Signs of deer or elk with either acidosis or enterotoxemia are similar and indistinguishable in the field. The signs can include dehydration, diarrhea, incoordination, convulsions, and depression. Death may occur within 24-72 hours of excessive grain ingestion.

Bovine Tuberculosis (TB)

Bovine Tuberculosis (bovine TB) is a contagious respiratory disease caused by the bacterium Mycobacterium bovis. Bovine TB can infect most warm-blooded animals, including humans. The federal government has done nationwide testing of cattle herds to control bovine TB, but it still occurs sporadically in cattle and wildlife such as elk and deer. Bovine TB has been diagnosed in captive elk and red deer herds in several states including Wisconsin. Michigan has found TB in their free-ranging white-tailed deer since 1994, and Minnesota has found TB in their free-ranging white-tailed deer since 2005.

Deer ribcage with TB lumps.
TB is a slowly progressive disease in deer. It can take years before the typical yellow or tan lumps appear inside the ribcage or on the lungs.
©MI DNR Rose Lake Disease Laboratory

Bovine TB is a progressive, chronic disease. It can take months to years from the time of infection until the development of clinical signs. The lymph nodes in the animal's head usually show infection first, and as the disease progresses lesions will begin to develop on the surface of the lungs and chest cavity.

The DNR does not believe the state's wild deer population is infected with TB. Since 1996, more than 150,000 deer in Wisconsin have been screened for bovine TB, and no evidence of the disease has been found. The department will continue annual TB screening. As a hunter, you may be asked by DNR staff to provide a sample from your deer for TB and other disease screening. This is voluntary, but your cooperation is important in detecting this disease.

Transmission of bovine TB from animals to people can occur, but it is rare. Bovine TB is generally transmitted through the air by coughing and sneezing, and it is highly unlikely a person would contract the disease from field dressing or eating the meat of an infected deer. However, it is always a good idea to wear gloves when field dressing any animal. There is no specific test that can be easily done to check for TB in deer meat.

Brain Abscesses or Cranial Abscessation Syndrome (CAS)

External sign of CAS
Swollen eye and pus at pedicle.

Brain abscesses are usually caused when Trueperella pyogenes (formerly known as Arcanobacterium or actinomyces pyogenes) bacteria enter a wound in the velvet of a buck's antlers, through a broken antler or through the pedicle (antler base) after antlers shed. After entering through a wound, the bacteria can actually damage the bone of the skull sufficiently to penetrate and cause an abscess in the brain.

Adult antlered deer from all over Wisconsin have been diagnosed with cranial abscessation syndrome (CAS). Bucks appear blind, uncoordinated and may show abnormal behavior such as aggression toward people and stationary objects, or not moving when approached by people or dogs. Signs of CAS include swollen eyes, broken antlers weeping fluid, swollen joints, foot sores and lameness. Pus may be observed at the pedicle or in eye sockets. CAS is more common in bucks than does, likely because the bacteria enter wounds that result from sparring between bucks; according to studies in other states, CAS may account for up to 6 percent of natural mortality in bucks.

Internal sign of CAS

Abscess extending from antler pedicle through skull into brain.

If you harvest an adult buck with pus weeping from antler pedicles or eye sockets, the deer may have this bacterial infection. Though the meat may be contaminated with the CAS-causing bacteria, the infection is usually limited to the head. No part of the head should be eaten. The other meat is likely safe to eat, as normal cooking temperatures will destroy the bacteria.

Hemorrhagic disease (HD)

Hemorrhagic disease (HD) is an acute, infectious, often fatal, viral disease that affects white-tailed deer as well as other hoofed animals. In areas where HD regularly occurs, death rates are lower, usually less than 25 percent of the population. In areas where the disease rarely occurs, like here in Wisconsin, death rates can be much higher. High-density deer herds may have higher mortality rates. The disease is caused by either bluetongue virus or the epizootic hemorrhagic disease virus (EHDV); however, the visible signs of the disease are virtually indistinguishable with both the viruses. The disease is transmitted by biting flies often referred to as no-see-ums (Culicoides midges). The virus does not survive long outside the insect or the deer host.

Fawn with hemorrhagic disease
White-tailed deer fawn found with HD © Melissa Clark

Deer can display multiple symptoms depending on how long they are infected. Deer that are infected and have the most severe cases of the disease may be unafraid of humans, salivate excessively, have foam present around the nose (sometimes with blood), appear weak but in good body condition and may appear to have swollen areas of their body (typically areas of the head and neck). Deer may also be found in or near water as they can develop very high fevers and be dehydrated. In some instances of the more chronic form of the disease, deer may have erosions or ulcerations in their mouth, be very thin, and have detachment of the wall of their hoof making it very hard for them to walk. In deer that recover, abnormal hoof growth may be noted.

HD in Wisconsin

The disease was diagnosed for the first time in Wisconsin deer in 2002, when approximately 14 deer were found suddenly dead in Iowa County during September. Between 2002 and 2011, deer surveyed and tested did not identify HD activity which suggests HD does not occur commonly in Wisconsin. However, in the fall of 2012 deer found dead in eight southern Wisconsin counties tested positive for Epizootic Hemorrhagic Disease (EHD). We are not yet sure what this will mean in regards to EHDV in Wisconsin and we will continue to be on the alert for outbreaks in the future. There is still much we need to learn about HD in Wisconsin deer, so please continue to report any unusual observations of dead deer to your local DNR office.

The viruses that cause hemorrhagic disease do not infect humans. Therefore, humans are not at risk when handling infected deer, eating venison from infected deer or being bitten by infected Culicoides midges (no-see-ums).

Additional Information

Deer fibromas

Facial fibromas.
White-tailed deer with facial fibromas

Fibromas are firm, nodular, fleshy masses attached to the skin. They are commonly described as warts. Fibromas vary in size from less than one inch to more than four inches in diameter, and they can be found anywhere on the deer's body, but are most common on the face, neck and forelegs. Fibromas are caused by a virus which is transmitted by insects. Infected deer usually mount an immune response, and the fibromas eventually disappear. Occasionally, a deer will be severely infected with multiple fibromas which interfere with the eyes or normal use of the legs, causing health problems for the deer. Fibromas cause no damage to the meat, which is safe to consume.

Nasal bot flies

nasal bots in throat.
Bots in nasal pasages of a deer.

nasal bots larvae.
Bot fly larvae.

Nasal bot flies (Cephenemyia sp.) are common parasites that are found in the nasal passages of deer. Adult female flies deposit eggs in the nostrils of the deer. The eggs hatch into larvae and then pass through several stages of development and growth while living in the nasal passages. Although quite large - up to 1 1/2 inches - and unpleasant looking in the final stages of development, nasal bots cause little harm to individual deer and do not infect humans. Bot flies do not affect meat quality, and it is safe to eat meat from an animal infected with bots.

Chronic wasting disease

Chronic wasting disease (CWD) is a fatal nervous system disease affecting deer, elk and moose. Clinical signs of CWD include no fear of humans, teeth grinding, notable weakness, drooping of head and ears, excessive thirst, difficulty swallowing, rough dull coat, walking in set patterns, nervousness, loss of coordination, excessive salivation, diminished tone of facial muscles, excessive urination, severe emaciation and dehydration and inability to stand. Please view the CWD pages for more information on CWD in Wisconsin.

Liver flukes

Liver flukes.
The arrow above points to flukes in a partially dissected white-tailed deer liver.

Liver flukes are a parasite that may be found in the liver of some deer. Adult flukes are flat, oval-shaped, purple-gray in color and look like leeches or "bloodsuckers." The flukes vary in size from 15-30 millimeters (mm) wide, by 30-100mm long, by 2-5mm thick. Even though the flukes may cause local damage to the liver, it is rare that the presence of liver flukes significantly affects the health of the deer. Consumption of venison from an infected deer poses no risk to humans. However, the liver of an infected deer should not be consumed as the fluke-damaged areas of the liver can be secondarily infected by bacteria which could impact human health.

Last revised: Wednesday February 15 2017