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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.

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

Diseases and conditions

Bovine tuberculosis surveillance

Due to a recent confirmation of tuberculosis in a Dane County dairy farm the department will be testing wild white-tailed deer for bovine TB.

Below is a list of diseases that are either commonly found in Wisconsin wildlife or that the DNR is monitoring for their occurrence in Wisconsin wildlife. Help monitor the health of Wisconsin's wildlife by reporting your sightings of sick or dead wildlife to your local DNR office. It is not necessary to report wildlife killed along roadways.

Avian Botulism

Avian botulism is a neuromuscular illness caused by a toxin that is produced by the bacteria Clostridium botulinum. There are seven types of botulism toxins (A-G). Wild birds are affected by type C and type E. These bacteria typically live in lake, pond or wetland substrates and sporadically produce toxin when certain environmental conditions develop. Environmental conditions thought to contribute to toxin production include high water temperatures and low oxygen levels in the water. Two invasive species may also play a role in transmission of the toxin in the Great Lakes. These are the zebra mussel and a small fish called the round gobie.

Dead birds on the beach
Botulism type E has been implicated in waterbird die-offs in the Great Lakes since the 1960s


Botulism outbreaks in wildlife occur when invertebrates or fish ingest the bacteria. If sub-optimal water conditions lead to deaths of these invertebrates or fish, the bacteria multiply in the dead animals and produce the toxin. Waterfowl, such as mallards, and fish-eating birds, such as loons and gulls, are then affected by the toxin contained within the invertebrates or fish that they eat. When these birds die, maggots consuming the carcasses pick up the toxin and any other bird or mammal that scavenges the carcasses can also be affected by the toxin.

Clinical Signs

The toxin interferes with nerve transmission to the muscles. Signs observed in affected birds will vary depending on how much toxin was ingested. Birds will have progressive muscle weakness and are observed having difficulty flying or standing. The paralysis can eventually reach the muscles needed for breathing. Waterfowl may become unable to hold their heads up and drown.

Disease Management

In Wisconsin, botulism type C and botulism type E have both been documented to cause significant mortality in water birds and fish. Botulism type C is usually associated with waterfowl die-offs on smaller lakes and wetlands, while botulism type E is known to cause die-offs among fish-eating birds, such as common loons and gulls, in the Great Lakes ecosystems.

Because the Clostridium bacteria are naturally found in the environment there are no easy control methods for preventing outbreaks of botulism in wildlife. Wildlife mortality commonly occurs in the fall when water temperatures are high and water levels are low. On some smaller lakes, water level controls may be helpful in reducing the effects of botulism. Control of the invasive species linked with botulism may also help to reduce the occurrence of mortality due to botulism on the Great Lakes. Removing and properly disposing of carcasses during a botulism event decreases the availability of toxin and risk to additional wildlife.

Public Health

Botulism in people is usually due to type A or B toxins from consuming home-canned foods that were improperly preserved or from damaged store-bought canned foods. Type C botulism in not known to affect people. Humans can become sick from type E from consuming affected fish, but proper cooking will inactivate the toxin. Besides cooking fish or waterfowl to the recommended temperature, it is never a good idea to eat fish or birds that appear sick or are found dead. Precautions should always be taken when handling carcasses, including wearing gloves and washing hands. Additionally, pets should be kept away from carcasses.

Additional Information

Avian influenza

Avian influenza (AI) is caused by a virus that is common in wild bird populations, especially shorebirds and waterfowl. There are many different subtypes of AI and in general, most subtypes do not cause obvious signs of disease in wild birds or have the ability to infect animals other than birds.

Avian influenza viruses can cause disease in domestic birds with the severity of the infection depending on the subtype and gene assortment of the virus that is involved. In rare instances, mortalities in wild birds can occur.


Typically, avian influenza viruses are shed in the feces of wild birds that carry the virus and transmission between wild birds is believed to primarily occur through ingestion of the virus. AI viruses typically increase in wild bird populations during the late summer and early fall pre-migration staging when previously un-exposed, juvenile birds begin to concentrate in areas with older ducks, many of which are carriers.

Clinical signs

Waterfowl in Wisconsin
In Wisconsin, avian influenza viruses are common in shorebirds and waterfowl.

Signs of AI in wild birds vary depending on the viral subtype, environmental stress and bird species. In wild birds, infections with AI typically do not show any clinical signs.

Disease Management

The department monitors for AI in free-ranging wild birds in Wisconsin throughout the year through investigations of wild bird mortality events involving five or more birds. The DNR, in cooperation with the USGS National Wildlife Health Center and others, has enhanced surveillance efforts based on apparent species susceptibility, reported clinical signs and proximity to any reported mortality events in wild birds.

Investigating sick or dead wild bird events is an effective tool for early detection of AI outbreaks. If you observe five or more sick or dead birds in one area please contact your local DNR office. In Wisconsin, if you find sick or dead birds from May 1 through October 31, contact the dead bird hotline at 1-800-433-1610.

Public health

For information on symptoms of avian influenza in humans and related resources please visit Human health and Avian Influenza A (H5N1) Virus [exit DNR]

The majority of AI viruses do not infect humans, however simple precautions should be taken to reduce or minimize the risks of infection.

  • Do not handle sick or dead wild birds.
  • Wash hands thoroughly with soap and water after contact with a wild bird or contaminated surfaces (including bird baths and feeders). Flu viruses are inactivated by common disinfectants including detergents, 10% bleach solution and alcohol.
  • Cook all meat, including wild birds and poultry thoroughly to a temperature of 165° F to kill organisms and parasites.
  • Hunters should sanitize all tools and surfaces when handling, cleaning and preparing wild birds.
  • Wear disposable gloves when cleaning bird feeders and baths.

Additional Information

Information for domestic poultry owners

Information for hunters

Avian pox

Avian pox is an infectious disease of birds caused by a poxvirus belonging to a group of viruses called avipoxviruses. Avian pox is a slowly developing disease that can affect a number of wild bird species, including turkeys and songbirds.

There are two forms of the disease: a cutaneous (dry) form and a diphtheritic (wet) form. In the cutaneous form, warty lesions are observed on the featherless areas of the skin of the head, neck and legs. In the wet form, lesions can form in the respiratory tract and upper gastrointestinal tract and can interfere with eating and breathing. In Wisconsin, wild turkeys are commonly reported with pox-like lesions and at least one wild turkey has been confirmed at necropsy to have died from the wet form of avian pox infection.


The virus can be transmitted to birds by insect vectors, especially mosquitoes. Other routes of transmission include direct contact between infected birds and susceptible birds and contact with food, water or other surfaces that have been contaminated from lesions from infected birds.

Clinical signs

Severity of the disease in wild birds can vary from mild to severe. Birds with mild signs of warty lesions on the skin generally recover. In more severe cases of the disease, the lesions interfere with the bird’s ability to see, eat, breath or move. Secondary bacterial infections may also occur. The wet form of the disease causes more severe signs and can cause severe respiratory disease. Wild birds with severe disease may appear emaciated and lethargic.

Disease Management

Control of avian pox in wild birds includes reducing potential transmission to unaffected birds. When visibly affected birds are present, bird feeders and bird baths should be removed and disinfected with a 10% bleach solution. Feeders and baths should not be put back up until the affected birds are gone from the area. Eliminating sources of standing water where mosquito vectors breed can also help reduce the chance of transmission.

Public health

There is no evidence that the strains of poxvirus that affect wild birds causes disease in humans.

Additional information

Bovine tuberculosis (TB)

Bovine Tuberculosis (bovine TB) is a respiratory disease caused by the bacterium Mycobacterium bovis. Bovine TB can infect most mammals, including white-tailed deer and 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 does not spread easily. It is a chronic, slowly progressing disease, which means it can take months or years to worsen, grow or spread. It is most commonly spread between animals through nasal secretions. This can occur through close nose-to-nose contact, coughing and sneezing in close contact, and sharing contaminated feed.

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

Clinical Signs

Most deer with bovine TB have no visible signs of illness. The disease progresses very slowly, and in later stages deer may show signs of respiratory illness, such as coughing, nasal discharge, difficulty breathing and may look thin or emaciated. Bovine TB causes lesion most commonly found in lymph nodes of the head in harvested deer but may also appear as tan or yellow lumps (small abscesses) on the inside surface of the rib cage and/or the lungs. Very rarely, abscesses may be identified in other organs.

Disease Management

The Department annually screens for bovine TB all harvested deer samples that are submitted for chronic wasting disease testing. Since 1996, more than 150,000 deer in Wisconsin have been screened for bovine TB and no evidence of the disease has been found. Early detection of bovine TB in deer and herd management are the only effective tools for keeping bovine TB out of Wisconsin deer.

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.

Public Health

Transmission of bovine TB from animals to people can occur, but it is rare. Bovine TB is most commonly spread to humans through consuming unpasteurized milk or milk products from infected animals, and close contact with infected animals or people.

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.

Additional Information

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.

Canine distemper virus (CDV)

Canine distemper virus affects mainly raccoon and gray fox populations, but can also infect other carnivores. This disease can be transmitted to domestic dogs, but is not a risk to people. Infected animals appear lethargic and may show no fear of humans, wander aimlessly, have respiratory signs, discharge from the eyes or nervous system signs such as convulsions and chewing fits. Signs of CDV mimic those of rabies, making it difficult to tell what disease it is without testing. The virus does not live long outside the diseased animal, and is destroyed by most soaps and disinfectants, including bleach.

Canine parvovirus (CPV)

This highly contagious viral disease affects fox, wolf, coyote and raccoons and is most severe in young animals. Canine parvovirus can be transmitted to domestic dogs, but is not a risk to people. This disease causes intestinal bleeding, severe diarrhea and dehydration which may result in death. The virus is shed through the feces, and persists in the environment. A 10% bleach solution inactivates the virus.

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.

Corn toxicity in ruminants
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.

Deer fibroma

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.

Deer 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.

Deer 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.

Epizootic hemorrhagic disease (EHD) in WI deer

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

coyote with mange

Mange is caused by a microscopic mite, and in Wisconsin most commonly occurs in coyote, red fox and wolf. This type of mange may also be transmitted to domestic dogs. Mange-affected animals lose hair and develop thick, scaley skin. They can die of starvation, dehydration or hypothermia during the winter. Sarcoptic mange mites can occasionally infect people. Clinical signs of mange in people include a localized, itchy red rash.

Newcastle disease

Newcastle Disease (NDV) is a contagious viral disease of birds. Signs of disease in birds vary from mild to severe depending on the strain of the virus. In general, wild waterfowl species appear to be relatively resistant to the highly infectious form of the disease. In Wisconsin wild bird populations, periodic outbreaks of NDV has resulted in illness and death in breeding colonies of Double-Crested Cormorants during the months of March - September.

Double-Crested Cormorant
In Wisconsin, outbreaks of Newcastle disease virus have only resulted in illness and death in cormorants. © Melissa Clark


Birds infected with NDV shed the virus in exhaled air and other bodily discharges including feces. The virus can also be present in eggs and in the carcass of a dead bird. Susceptible birds can become infected by breathing in the virus or by ingesting food or water that is contaminated.

NDV is capable of surviving in the environment and on objects such as shoes and clothing. It is possible for healthy birds to become infected after contact with contaminated objects.

Clinical signs

NVD in birds can vary from no signs of disease to sudden death. In wild populations, signs of infection have only been observed in juvenile double-crested cormorants. These signs have included the twisting of the head or neck, lack of coordination, shaking, or paralysis of one or both wings or legs.

Carcass of cormorant
NVD is capable of surviving on a carcass. If you find a sick or dead bird, contact the Wisconsin Dead Bird hotline. © Melissa Clark

Public health

Newcastle disease infection in humans is rare and usually mild, typically only affecting people in direct contact with infected birds. Signs of infection in humans include conjunctivitis (swelling and reddening of the tissue around the eyes) and mild flu-like symptoms.

When working with or handling birds, there are simple precautions one can take.

  • Wear gloves and safety glasses.
  • Wash your hands after contact with birds or poultry.
  • Avoid touching your eyes until your hands have been washed.

Wildlife management

Control of NDV in wild populations is difficult as large amounts of the virus are shed by infected birds, contaminating the surrounding environment. During an outbreak of Newcastle disease, it is important to identify the outbreak site as a contaminated area and take steps to minimize the spread of the disease to other areas. The U.S. Department of the Interior along with Wisconsin DNR routinely investigate mortality events when large numbers of birds are involved. Investigating sick or dead wild bird events is an effective tool for detection of NDV outbreaks. In Wisconsin, if you find sick or dead birds, contact the dead bird hotline at 1-800-433-1610.


Rabies is a viral disease of the central nervous system. It is transmitted by scratches, bites or having an open wound or mucous membrane contact an infected animal's saliva. Skunks and bats are the main rabies carriers in Wisconsin wildlife, but all warm-blooded animals, including humans, are susceptible to rabies. Infected animals can show abnormal activity, can be aggressive, show no fear of humans and may salivate excessively ("foaming at the mouth"). They may be lethargic or wander aimlessly. Sporadic convulsions, tremors and chewing fits can also be signs of rabies.

Anyone who has been bitten, scratched or has an open wound or mucous membrane or has come into contact with fresh saliva of a wild animal is considered at risk for rabies. You should IMMEDIATELY clean the bite, wound or scratch with soap and water.

Little brown bat
Bats rarely carry rabies but bats should be tested if a person or pet is exposed. © Melissa Clark

Contact your local health department [exit DNR] as soon as possible to report the incident and for further guidance. Health officials will evaluate the risk, based on the wild animal species involved and other factors, and decide if there is a need to capture and euthanize the wild animal for laboratory testing. The person who is bitten should seek immediate medical attention. For additional information on rabies in Wisconsin please see the Wisconsin Department of Health Services rabies information [exit DNR].

The WI Departent of Health advises that "Because bites and scratches from bats may go unnoticed if a person is sleeping, is very young, or is mentally incapacitated, a physician should be contacted if a bat is found in the same room with a young child, or with a sleeping or mentally incapacitated adult. Persons who have been in close physical proximity to bats and who cannot rule out the possibility of physical contact should likewise contact their physician."

If a pet or domestic livestock has had a possible interaction with wildlife contact your veterinarian. Dead wildlife carcasses may still harbor live rabies virus and could potentially infect pets that come into contact with them.

Raccoon roundworm

The raccoon round worm generally does not harm the raccoon, but simply lives in the intestinal tract. Raccoons that have adult worms release parasitic eggs in their feces. People and animals other than raccoons can accidentally ingest these eggs, which may be on the ground, on surrounding vegetation or in cages or enclosures. Once the eggs are ingested, they can hatch into larvae. The larvae can move through the body, causing harm to the nervous system or eyes and can even result in death. There is no reliably successful treatment to rid the roundworms in people.

Raccoon roundworms are very hardy and can only be killed by intense heat or boiling lye. Gloves and a mask should be worn when handling raccoon fecal material or anything that may have been contaminated with raccoon feces.


Salmonellosis is a bacterial disease that infects a variety of species including mammals, reptiles and birds. There are many strains of the bacteria all belonging to the genus Salmonella. Salmonellosis is found in most avian species throughout the world, including North America.


The bacteria that cause salmonellosis live in the intestinal tract of infected birds and are shed through feces. The organism can be spread from an infected bird to a healthy bird through direct contact or through the ingestion of food or water that has been contaminated with infected fecal matter.

In Wisconsin, outbreaks of salmonellosis are typically seen in passerine species (a large group of perching birds) during late winter and early spring when birds are stressed and congregate around bird feeders and bird baths.

Clinical signs

Signs of salmonellosis vary greatly and are dependent on age, species, bacterial strain and environmental stressors. Birds may shows signs ranging from a gradual onset of disease to sudden death. Infected birds may appear "fluffed-up" and huddled together and may be shivering. The can also have seizures, weight loss and watery yellow to green tinged feces.

Public health

The bacteria causing salmonellosis in wild birds do have the ability to infect humans. Humans can minimize the risk of infection by wearing disposable gloves and taking extra care in personal hygiene when handling materials soiled by bird feces, including feeders, bird baths and bird houses.

Wildlife management

Salmonellosis does not contribute to substantial population decline in wild bird species and are more of an interest to individuals who provide bird feeders and birdbaths. Often, outbreaks of salmonellosis are mistaken for poisoning. If you find a group of dead birds, contact your local DNR office for more information.

Individuals can take simple precautions to reduce the risk of transmission of salmonellosis in wild birds.

  • Clean feeders, feeding areas and birdbaths using a 10 percent bleach solution.
  • Remove seed hulls under bird feeders.
  • Move feeders occasionally to prevent the buildup of excrement underneath the feeder.
  • Add additional feeders to reduce over-crowding and contamination.
  • Keep seeds and food dry.
  • Change the water in birdbaths regularly.
  • If a sick or dead bird is found near a feeder or birdbath, remove it, clean it using the 10 percent bleach and wait at least a week before putting it back up. If possible, move it to a new location.
Squirrel pox

Squirrel pox, also called squirrel fibroma, is caused by a pox virus, called squirrel fibroma virus, that is related to other pox viruses. This disease is characterized by varying sizes and numbers of wart-like growths or fibromas on the skin of squirrels. In Wisconsin, gray squirrels with pox-like lesions are routinely reported in small numbers each year. Juvenile squirrels may be more susceptible.


Biting insects, such as mosquitos, are the primary route of transmission between squirrels.

Clinical signs

Affected squirrels can have growths of varying size and number on the skin. These growths can appear on any part of the skin.

Wildlife Management and Prevention

Squirrels with fibromas generally recover as the growths resolve and disappear. In severe cases, the growths can interfere with the squirrel’s ability to see, eat, or move and can lead to starvation or increased risk of predation. Eliminating sources of standing water where mosquito vectors breed can help reduce the chance of transmission in the wild.

Public Health

The squirrel pox virus is not known to infect people.

Additional Information

Trichomoniasis in birds

Trichomoniasis is an infectious disease of birds that is caused by a protozoan (single-celled) parasite, Trichomonas gallinae. Pigeons and doves are mostly affected, but other species, such as finches, can become infected. In Wisconsin, it has been identified as the cause of mortality in both mourning doves, purple finches, house finches and in one peregrine falcon.


This parasite is commonly found in the upper gastrointestinal tract of adult pigeons and doves and can be transmitted to their young during the feeding process where adult regurgitate food for their offspring. Food and water sources such as backyard bird feeders and bird baths can become contaminated from the mouths of infected birds. Raptors, such as peregrine falcons, that prey on small birds, can become infected from eating infected prey.

Clinical signs

In general, sick birds appear weak and have a “fluffed up” appearance. The parasite causes inflammation of the linings of the crop and mouth. As the disease progresses ulcers form which become masses that eventually cause blockages within the mouth. Birds appear to have difficulty swallowing or breathing.

Wildlife management and prevention

Not all birds that are infected with this parasite become sick. Once the noticeable lesions appear, affected birds generally are at risk of starvation or suffocation. Control of the trichomoniasis in wild birds includes reducing potential transmission to unaffected birds. When visibly affected birds are present, bird feeders and bird baths should be removed and disinfected with a 10% bleach solution. Feeders and baths should not be put back up until the affected birds are gone from the area.

Public health

This parasite does not infect people.

Additional information

Tularemia (rabbit fever, beaver fever)

Tularemia is also known as "beaver fever" or "rabbit fever". This bacterial disease is most frequently found in Wisconsin muskrat, beaver or rabbits. An infected animal will generally be in good physical condition, but have an enlarged spleen or liver covered with small white spots.

This disease can be transmitted to humans by biting insects, such as flies and ticks, direct contact and by ingestion of poorly cooked meat. The most common symptoms for humans are a slow-healing skin sore or ulcer, swollen lymph nodes and fever. Ingestion can lead to abdominal pain, diarrhea and vomiting. Tularemia can only be diagnosed with laboratory testing and treatment usually results in full recovery.

Tyzzer's disease (Clostridium piliforme)

Tyzzer's disease is a bacterial infection that is seen in muskrats and cottontail rabbits. It is not a disease risk for people. Animals are usually found dead in good physical condition, as animals can get sick and die within a few hours after infection. Overpopulation, limited food resources and other stress factors may contribute to outbreaks of this disease. Animals with Tyzzer's disease have blood engorged organs, but only laboratory testing can confirm this infection. Signs of Tyzzer's disease mimic those of tularemia.

Warbles (Cuterebra botfly larvae)

Warbles is a term that describes bumps under the skin that are caused by infection with fly larvae. In wild mammals this condition involves the larvae of the botfly, Cuterebra sp. Cuterebra warbles are most commonly seen in squirrels, chipmunks, rabbits and other small mammals.


Female bot flies lay their eggs along mammal paths and at entrances to small mammal burrows. When the eggs hatch, the fly larvae enter the mammal through the nose, mouth or a wound in the skin. The larvae then travel to an area of the body just under the skin to complete development.

Clinical signs

Wild mammals infected with warbles will have a noticeable bumps or bumps under the skin. There may be an opening caused by the larva prior to leaving the body. Depending on the part of the body affected, movement of the wild mammal may be hindered.

Wildlife management and prevention

Generally, infected individuals recover after the bot fly larva emerges from the under the skin and falls off. Occasionally, a secondary bacterial infection may occur at the site of the skin wound created by the emerging larva. This parasite rarely has a significant effect on populations and affected individuals usually recover.

Public health

There is no public health concern with this parasite.

Additional information

West nile virus

West Nile Virus (WNV) is a viral disease that was commonly found in Africa, Europe, the Middle East and West Asia. It first appeared in New York in 1999 and has quickly spread throughout North America. It was first detected in Wisconsin in 2001. WNV has been documented in over 250 species of birds and several species of mammals, including humans.

How to report a sick/dead bird.


WNV is spread through the bite of infected mosquitos. After feeding on an infected bird, the virus eventually ends up in the salivary gland of the mosquito. The virus can then be transmitted to other birds or mammals, including humans. Many species of birds can act as a natural host for WNV, circulating the virus in their blood for a few days after becoming infected.

Clinical signs

Many species of birds can be infected with WNV without showing symptoms; however corvid species (including blue jays and crows), some raptors and species of birds that have never been exposed to the virus can die from the infection. Signs of infection in birds may not appear until the last stage of the disease, when the brain becomes inflamed. These signs may include being unable to fly or walk properly or trouble standing upright. Often, birds die suddenly after exhibiting no signs at all.

Public health

Humans are susceptible to WNV, however, typically only a small number of people exposed to the virus become infected. People who do become infected with WNV typically either have no symptoms or a mild, flu-like disease. In some cases, usually among the elderly, WNV causes serious disease that affects the brain tissue and can be is fatal.

People should take precautions in areas where WNV activity is high. Reducing exposure to mosquitoes is the best method of control. More information about reducing exposure to WNV can be found at the Wisconsin Department of Health website [exit DNR].

Wildlife management

WNV was first detected in North America in 1999 and it is very likely that our native bird populations had not previously been exposed to this virus. As such, it appears that there were high rates of infection and possibly death as these birds did not have sufficient immunity to the virus.

Currently, the effects of WNV on bird populations in Wisconsin and the rest of North America are unknown. Some simple precautions can be taken to help reduce to spread of the virus.

  • Eliminate stagnant water from your property.
  • Regularly clean birds baths.
  • Empty water-filled containers where mosquitoes may breed.


If you find a sick/dead corvid (crow or jay) call the Dead Bird Reporting Hotline at 1-800-433-1610. This hotline set up by Wisconsin state health officials will be available for callers from May through October.

If any other birds or mammals are showing clinical signs of WNV contact your local DNR office.

Last revised: Monday January 28 2019