Wildlife Habitat_Content Page_WildlifeDiseases

Wildlife Diseases

Below is a list of diseases and other health issues that are either commonly found in Wisconsin wildlife or that the DNR is monitoring for their occurrence. Click on a specific disease to learn more about the disease, how it is transmitted, common signs observed in affected wildlife, management actions, any associated public health concerns and links to additional information.

You can help monitor the health of Wisconsin's wildlife by reporting your sightings of sick or dead wildlife to the DNR. To report a sick or dead bird, please use this survey form: Sick or Dead Bird Reporting Form. Or you can contact the Wildlife Hotline to report a sick or dead mammal or bird by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff. In your message, please include the number of animals, the species (such as a raccoon or Canada goose), if they were sick or dead, the specific location where you saw them, including the county and your contact information. 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 lakes, ponds or wetland substrates and sporadically produce toxins 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 the transmission of the toxin in the Great Lakes. These are the zebra mussel and a small fish called the round goby.

Transmission

Botulism outbreaks in wildlife occur when invertebrates or fish ingest the bacteria. If sub-optimal water conditions lead to the 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 many toxins were ingested. Birds will have progressive muscle weakness and are observed to have 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 help reduce 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 toxins and risks 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 is 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 cholera

Avian cholera is a common waterfowl disease that most frequently affects waterfowl and coots, followed by scavenger bird species and other water birds. It is caused by the bacterium, Pasteurella multocida, which is highly contagious among birds and swiftly spreads through large congregations of waterfowl. In North America, this disease was first reported in 1944 and is the cause of the large-scale mortality of waterfowl in many states.

While it is seen annually in western states, especially in Snow geese and Ross’s geese, it has only been documented occasionally in Wisconsin. Avian cholera was the cause of mortality of over 800 mallards and Canada geese on Horicon Marsh from the fall of 1979 to the spring of 1980 and over 3,800 double-crested cormorants in Green Bay in the fall of 2019.

Transmission

Transmission of the bacteria can occur through bird-to-bird contact or from infected carcasses, water, soil, boots and equipment. Birds that survive infection can become sources of infection with the potential to spread the bacteria throughout a flyway.

Clinical signs

Affected waterfowl may become sick very rapidly and the first signs of an outbreak may be multiple dead birds. Sick birds may be weak, twist their heads and necks over their back, have convulsions, swim in circles and fly erratically.

Disease management

Management includes monitoring areas with high concentrations of waterfowl for mortality and promptly removing sick and dead birds to reduce the spread of the bacteria. The bacteria are easily killed with most disinfectants, including 10% bleach.

Public health

The bacterial strain that affects birds does not generally affect people and the human disease known as cholera is not the same disease as avian cholera.

Additional information

Avian influenza

Avian influenza (AI) is caused by a virus that is common in wild bird populations, especially waterfowl and shorebirds. Avian influenza viruses are identified by two specific protein groups: Hemagglutinin or the “H” of which there are 16 and neuraminidase or “N” of which there are 9. Combinations of these 2 create a subtype of the virus (ex: H1N1, H5N2, etc). There are many different subtypes of AI and in general, most subtypes do not cause obvious signs of disease in wild birds. Waterfowl often carry avian influenza viruses naturally in their gastrointestinal tract, often without causing disease, but there have been rare strains that may also cause disease in some wild birds (including some species of waterfowl) or other animals.

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. The pathogenicity identification (low or highly pathogenic avian influenza) refers to how lethal the identified type and strain of the virus is to domestic poultry.

Transmission

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 the 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. When AI viruses cause disease, those birds often shed viruses from their respiratory tracts as well.

Clinical signs

Signs of AI in wild birds vary depending on the viral subtype, environmental stress and bird species, and are not specific to the disease associated with this virus. In wild birds, infections with AI typically do not show any clinical signs. When birds do show clinical signs, they can be respiratory (sneezing, coughing, ocular and nasal discharge, edema surrounding the eyes); neurological (abnormal position of the head, falling or tremors, circling); gastro-intestinal (diarrhea, green discoloration of feces) and just overall signs of not doing well including weakness.

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 the early detection of AI outbreaks. If you observe five or more sick or dead birds in one area, please contact the DNR Wildlife Hotline by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff to return your call. In your message, please include the number of animals, the species (such as Canada goose), if they were sick or dead, the specific location where you saw them, including the county and your contact information.

HPAI in other species

Sometimes, avian influenza viruses can cause other species of animals to become sick. In Wisconsin, the strain of H5N1 HPAI affecting wild and domestic birds in 2022 has been linked to a few cases of the disease in wild mammals including red foxes, bobcats, fishers, skunks and otters. Mammal species that may scavenge or hunt wild birds as part of their natural diet are likely exposed to the virus from eating infected wild birds. All of these affected mammals showed neurological signs. Neurological signs in mammals can signify many different conditions, including exposure to environmental contaminants, parasitic infections and diseases such as canine distemper and rabies. People should avoid approaching any wild mammal that appears sick, injured or behaving abnormally.

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 birdbaths 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.

Information for domestic poultry owners

Information for hunters

Wisconsin HPAI Detections:

Nationwide HPAI Detections

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 many 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.

Transmission

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 by lesions from infected birds.

Clinical signs

The 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, breathe 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 birdbaths 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 cause 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.

Transmission

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.

Clinical signs

Most deer with bovine TB show 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, and difficulty breathing and may look thin or emaciated. Bovine TB causes lesions 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 on 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 its free-ranging white-tailed deer since 1994, and Minnesota has found TB in its 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)

Brain abscesses in deer (also called cranial abscessation syndrome or CAS) are infections within the brain that produce abscesses that contain pus. The infections are usually caused by the bacterium Trueperella pyogenes. These bacteria are commonly found on the skin and gums of deer. Any deer can become infected with these bacteria and develop a brain abscess, however, it is most commonly reported in male deer.

Transmission

Infection occurs when bacteria enter a wound. It is most commonly seen in male deer when bacteria enter through a break in the velvet of a buck's antlers, through a broken antler or the pedicle (antler base) after antlers are shed. After entering through a wound, the bacteria can damage the bone of the skull sufficiently to penetrate and cause an abscess in the brain.

Clinical signs

Adult antlered deer from all over Wisconsin have been diagnosed with cranial abscessation syndrome (CAS). Deer may appear blind, and 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 base of the antlers or in eye sockets. This is more commonly reported in bucks than does, likely because the bacteria enter wounds that result from sparring between bucks.

Disease management

Because the bacteria that cause CAS are naturally occurring in the environment and infection is generally due to trauma from natural deer behavior, management is not practical. It only affects individual deer and is not spread from deer to deer.

Public health

Harvested deer that have pus at the base of the antlers or in or around the eyes 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. Normal cooking temperatures will destroy the bacteria, however, if any other part of the deer appeared abnormal it is best not to consume the meat.

Canine distemper virus (CDV)

Canine distemper is caused by a virus that affects and is easily transmitted between, raccoons, mammals in the canine family (fox, coyote, wolf, domestic dog) and the mustelid family (for example skunk, badger, otter, mink). It is common in Wisconsin to see localized mortality events associated with this virus, especially in raccoons, foxes and skunks. In Wisconsin, canine distemper has been documented as the cause of death in badgers, raccoons, coyotes, gray foxes, wolves, long-tailed weasels and striped skunks.

Transmission

The virus is highly contagious and is easily spread through respiratory secretions, urine, saliva and feces. Animals that have recovered from the virus can continue to shed it into the environment.

Clinical signs

Infected animals appear lethargic and may show no fear of humans, wander, aimlessly and have respiratory signs, and discharge from the eyes or nervous system signs such as convulsions and chewing fits. Signs of canine distemper are similar to those of rabies, making it difficult to tell which disease it is without testing.

Disease management

The virus does not live long outside the infected animal. It is destroyed by most soaps and disinfectants, including bleach.

Public health

The virus does not infect people. Domestic dogs are at risk. Dog owners should talk with their pet's veterinarian regarding vaccination.

Additional information

Canine parvovirus (CPV)

Canine parvovirus is a highly contagious viral disease that causes enteritis, which is inflammation of the intestines. The virus affects both wild canids, such as wolves and coyotes, and domestic dogs. Raccoons do not develop clinical diseases when exposed to canine parvovirus. Parvovirus in raccoons is caused by a virus that is very closely related to feline parvovirus and is identified as raccoon parvovirus.

Transmission

Parvovirus is shed through the feces and transmission occurs from oral contact with fecal material from infected animals. It also persists in the environment and indirect transmission can occur from contact with contaminated objects.

Clinical signs

The virus causes intestinal bleeding and signs include bloody diarrhea, weakness and dehydration.

Disease management

The virus can persist for many months and possibly years if protected from sunlight and desiccation. Carcasses should be isolated from other canids and incinerated or buried deeply. A 10% bleach solution inactivates the parvovirus.

Public health

The virus does not infect people. Domestic dogs are at risk. Dog owners should talk with their pet's veterinarian regarding vaccination.

Additional information

Chronic wasting disease

Chronic wasting disease (CWD) is a fatal nervous system disease affecting deer, elk, moose and caribou/reindeer. CWD belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs) thought to be caused by prions. The prions cause abnormal folding of specific normal proteins in the tissue cells which causes a characteristic spongy degeneration of the brains of infected animals.

Transmission

CWD transmission occurs when disease prions are shed by infected animals through saliva, urine, feces and natural decomposition after death. Because CWD prions bind to the substrate and are extremely resistant to the environment, the transmission may be both direct and indirect. This means that not only is CWD spread through contact between deer and their saliva, urine and feces, but also through contact between deer and contaminated environments. For more information, please see the department’s Recommendations For Reducing the Spread of CWD. [PDF]

Clinical signs

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.

Disease management

The Wisconsin Department of Natural Resources began monitoring the state's wild white-tailed deer for chronic wasting disease (CWD) in 1999. The first positives were found in 2002 through testing of hunter-harvested deer in November 2001. For information on the management of CWD in Wisconsin, please visit Wisconsin's Chronic Wasting Disease Response Plan.

Public health

The U.S. Centers for Disease Control and Prevention states that to date, there have been no reported cases of CWD infection in people. Nonetheless, as a precaution, the Wisconsin Department of Health Services (DHS) recommends that people only consume venison from healthy-appearing deer with test results indicating that CWD was not detected. This is consistent with recommendations from the Centers for Disease Control (CDC) [exit DNR] and World Health Organization (WHO) [exit DNR]. Information from the Wisconsin Division of Public Health is available through Venison and CWD: What Hunters Should Know. [PDF]

Additional information

Chytrid fungus (Bd) in amphibians

Chytridiomycosis or chytrid fungus is an emerging infectious disease of amphibians (both frogs and salamanders) and has been noted as the most devastating infectious wildlife disease recorded and a global threat to amphibian populations. Chytrid is an infectious disease caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd). The disease has been documented in amphibians from Wisconsin and the Midwest, but to date, large mortality events have yet to be noted in this region. Population declines, extirpations and extinctions have been found in other regions of North and South America. Bd is closely related to salamander chytrid disease (Bsal) which primarily impacts salamanders.

The history of Bd in the United States is not well understood, but the lineage may date back as far as 1000 years. The oldest verified record of chytrid fungus in North America is from California in 1928. Studies have shown the highest infection rates in amphibians are observed during spring, largely in colder, wetter months with post-metamorphic frogs being most susceptible. It appears some amphibians may be more resistant to Bd than other species.

Transmission

The fungi spread via zoospores, which can be transmitted through infected soil or water and possibly via direct contact between amphibians. Amphibians that spend higher amounts of time in terrestrial habitats may be more prone to infection. Bd affects the epidermal layer (skin) and can inhibit the ability of infected amphibians to effectively thermoregulate, perform oxygen exchange through the skin and hydrate themselves which can result in mortality. Models predict chytrid may move northward with greater prevalence and intensity due to climate change.

Clinical signs

Signs of the disease may vary by species, but common signs of infection are lethargy and loss of body weight, along with excessive shedding of skin or red skin, convulsions, inability to right themselves and abnormal feeding behavior.

Disease management

Currently little is known about the transmission of this fungus. The zoospores can be transported by people via clothes, boots or equipment. When sick or dead amphibians (tadpoles, salamanders, frogs) are observed, care should be taken to prevent potentially moving any infectious diseases to another location. At a minimum, rinse off footwear and either air dry in the sun for a few days, disinfect with a 10% bleach solution or wipe off with 70% alcohol wipes before wearing to another water area.

Public health

There is no known risk to people or pets.

Additional information

Chytrid fungus (Bsal) in salamanders

Salamander chytrid fungus (Batrachochytrium salamandrivorans or “Bsal”) was first identified in 2013 in Belgium and the Netherlands. Bsal impacts a variety of salamander species (as well as some frog species) and can result in mass mortality events. Bsal has not yet been documented in the United States but because we have the highest salamander diversity in the world, the introduction of this disease could have devastating consequences.

Transmission

The release of pet salamanders and frogs into the wild is the single largest cause of Bsal outbreaks.  Once Bsal is on the landscape, direct contact between salamanders or frogs is the most common method of spread, however contaminated water, soil or vegetation can also transmit the fungus.  Birds and other wildlife may inadvertently spread the fungus as well.

Clinical signs

Diseased salamanders are typically lethargic with noticeable skin lesions.  However, animals that appear healthy may also be carriers of the disease.

Disease management

Bsal has not yet been documented in the United States.  The introduction of this disease can be prevented by not releasing pet salamanders or frogs (native species or pet trade species) into the wild. When sick or dead amphibians (tadpoles, salamanders, frogs) are observed, care should be taken to prevent potentially moving any infectious diseases to another location. At a minimum, rinse off footwear and either air dry in the sun for a few days, disinfect with a 10% bleach solution or wipe off with 70% alcohol wipes before wearing to another water area.

Public health

There is no known risk to people or pets.

Additional information

Conjunctivitis in finches (Mycoplasmosis)

Conjunctivitis is a medical term to describe inflammation of the membrane that covers the front of the eye and lines the inside of the eyelids. The disease in wild birds was first identified in 1994 when house finches in Washington D.C. were reported with severe conjunctivitis with swollen eyes with runny or crusty discharges. The cause of this specific conjunctivitis in finches is a specific strain of bacteria called Mycoplasma gallisepticum. The disease is also called house finch eye disease, Mycoplasmal conjunctivitis or Mycoplasmosis. This disease is most common in house finches but has also been reported in purple finches, American goldfinches and evening grosbeaks. It has been found in house finches in nearly all states east of the Rocky Mountains. There are a few sporadic reports annually of conjunctivitis in finches in Wisconsin.

Transmission

The bacteria are transmitted between birds through the infective discharge from the eye. It is easily spread where birds congregate at roost sites, feeding areas, bird feeders and bird baths. Tube-type bird feeders are especially risky because the discharge from the eyes can easily be left on the openings of the feeders and transmitted to the next bird that arrives. The bacteria can also survive for short periods on contaminated materials such as dust, litter, feathers, bird feeders, boots and clothing.

Clinical signs

Affected birds have red, swollen eyes with a clear discharge. As the disease worsens, birds can develop a crusty layer around the eyes and the eyes can become swollen shut. The feathers around the eyes may become wet and matted and the birds will look fluffed out and become inactive.

Disease management

Preventing transmission to healthy birds is the best method of management. The public can take simple precautions to reduce the risk of transmission of mycoplasmosis in wild birds.

  • Clean feeders, feeding areas and birdbaths using a 10% 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 overcrowding 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 the feeder or birdbath, wash and disinfect it using the 10% bleach solution and wait at least a week before putting it back up. If possible, move it to a new location.

If you find a group of dead birds, contact the DNR Wildlife Hotline by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff to return your call. In your message, please include the number of animals, the species (such as goldfinch), if they were sick or dead, the specific location where you saw them, including the county and your contact information.

Public health

The bacteria that causes finch conjunctivitis does not infect people.

Additional information

Corn toxicity in ruminants

Corn toxicity refers to two diseases, acidosis (grain overload) and enterotoxemia (overeating disease). Both diseases can cause death in any ruminant, including white-tailed deer and elk, even those in good body condition. While these diseases can occur at any time of the year they are usually seen in late winter and are often associated with where well-meaning people have put out corn or other artificial foods for deer. The rapid change from a natural diet of high-fiber woody browse to a low-fiber/high carbohydrate diet as is found in grain, such as corn, can lead to either disease.

Transmission

In acidosis, the ingestion of large amounts of food high in carbohydrates like corn results in a change in the microflora (e.g. bacteria) 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 food high in carbohydrates like corn results in an overgrowth of the bacteria Clostridium perfringens. This overgrowth leads to the production of lethal amounts of toxins that are absorbed into the animal's body.

Clinical signs

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.

Disease management

These diseases are primarily the result of artificial feeding. Preventing deer from gaining access to stores of grain or other high-carbohydrate foods is the best way to prevent these diseases.

Public health

While corn toxicity cannot affect people directly, venison from any sick deer should not be consumed.

Additional information

Deer fibroma

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 papillomavirus.

Transmission

It is not known exactly how the virus is spread but it is thought that it may be spread by direct contact between deer. The virus may also be spread by biting insects.

Clinical signs

Fibromas only affects the skin of the deer and the only sign of this disease is the wart-like masses attached to the skin. 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.

Disease management

Infected deer usually mount an immune response and the fibromas eventually disappear.

Public health

The virus does not affect people and fibromas cause no damage to the meat, which is safe to consume.

Additional information

Deer liver flukes

Liver flukes (Fascioloides magna) are flatworm parasites that may be found in the liver of some deer. Adult flukes are purple-gray in color, flat and oval-shaped. The flukes vary in size from 1.5-3 cm wide to 3-10 cm long. They may look like leeches or blood clots when found in the liver. They are frequently surrounded by a fibrous capsule, in a dark, muddy-appearing fluid.

Transmission

Eggs from adult flukes pass in the feces of deer. The eggs hatch and the first stage, called miracidia, must enter a snail to continue development. After further development in the snail the next stage, called cercaria, leaves the snail and encyst on vegetation as infective larvae or metacercaria. A deer becomes infected when it eats the vegetation with the larval cyst which then penetrates the intestine of the deer and migrates to the liver where it becomes encapsulated as the adult fluke.

Clinical signs

There are no outward signs of the presence of liver flukes. In harvested deer, adult liver flukes may be found when the liver is sliced open. 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.

Disease management

Liver flukes do not significantly affect the wild deer population. Individual deer may have a varying degree of damage to the liver but is in good health, otherwise, they are generally not adversely affected.

Public health

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.

Additional information

Deer nasal bot flies

Nasal bots are the larvae of the bot fly (Cephenemyia sp.) and are common parasites that are found in the nasal passages of deer.

Transmission

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 deer.

Clinical signs

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. Some deer may be observed snorting or shaking their heads as the larvae may be irritating to the nasal passages.

Disease management

Nasal bots are not a significant health issue for deer and individual affected deer recover after the larvae finish development into adult flies and leave the body.

Public health

Nasal bots do not infect humans. Botflies do not affect meat quality and it is safe to eat meat from an animal infected with bots.

Additional information

Epizootic hemorrhagic disease (EHD) in WI deer

In the fall of 2021, epizootic hemorrhagic disease virus (EHDV) was confirmed in deer in La Crosse and Juneau counties. Reports of deer suspected to have died from EHD were less than 20 for each county. Deer were also tested in seven other counties but were negative for EHD. Those counties were Dane, Columbia, Crawford, Fond du Lac, Jackson, Pierce, and Polk.

Hemorrhagic disease (HD) is an acute, infectious, often fatal, viral disease that affects white-tailed deer as well as other hoofed animals. The disease is caused by either the bluetongue virus (BTV) or the epizootic hemorrhagic disease virus (EHDV). In areas where HD regularly occurs, death rates are lower, usually less than 25% of the population. In areas where the disease rarely occurs, like in Wisconsin, death rates can be much higher. High-density deer herds may have higher mortality rates.

The disease was diagnosed for the first time in Wisconsin deer in the fall of 2002 when approximately 14 deer were found suddenly dead in Iowa County. Between 2002 and 2011, blood samples from deer were collected and tested. The results did not find antibodies to the viruses that cause HD, which suggests that deer in Wisconsin are not routinely exposed to these viruses. Sporadic outbreaks of epizootic hemorrhagic disease occur in Wisconsin. In the fall of 2012, deer found dead in eight southern Wisconsin counties tested positive for epizootic hemorrhagic disease virus (EHDV). In the fall of 2019, EHDV has detected in deer found dead in southwestern Wisconsin. In the fall of 2020, there were small outbreaks of less than 50 deer each in Oconto and Buffalo counties. Department staff continues to monitor the deer herd for indications of HD and ask citizens to report any unusual observations of dead deer to the DNR Wildlife Hotline by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff to return your call. In your message, please include the number of deer, if they were sick or dead, the specific location where you saw them, including the county and your contact information.

Transmission

The viruses are transmitted by biting flies (Culicoides sp.) often referred to as no-see-ums or midges. The virus does not survive long outside the insect or the deer host. The hemorrhagic disease generally affects deer in the late summer and fall when the biting flies are most abundant. Outbreaks of this disease end after the first hard frost when insect populations fall.

Clinical signs

Visible signs of hemorrhagic disease are virtually indistinguishable between the two viruses (BTV and EHDV) that cause the disease. 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 the 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 Wisconsin, the disease has been detected only when groups of deer have been found dead, usually near water sources, and otherwise appeared to have been in good body condition. 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 a detachment of the wall of their hoof making it difficult for them to walk. In deer that recover, abnormal hoof growth may be noted.

Disease management

Wisconsin is on the far northern edge of the home range of the flies that carry the virus and so far only has sporadic outbreaks of this disease. If Wisconsin’s overall temperatures increase, it could allow the insects to expand their range farther northward and Wisconsin could see more outbreaks of this disease in the future.

Public health

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

Lead toxicity

Lead is a highly toxic heavy metal that is found in many types of ammunition and fishing tackle. Lead toxicity in wild birds occurs when they accidentally consume a source of lead through their normal feeding habits. Ingestion of lead from spent hunting ammunition or fishing tackle can cause illness or death in wild birds. Death from lead toxicity has been documented in Wisconsin in bald and golden eagles, common loons, trumpeter swans, turkey vultures, waterfowl and a whooping crane.

Transmission

Eagles can accidentally eat lead fragments found in the gut piles and carcasses of deer harvested with lead ammunition. Loons pick up small pebbles from the bottom of lakes as a part of their normal behavior to add grit to their crop (the upper part of their digestive tract) and frequently mistake lead fishing weights for small stones. Trumpeter swans feed by stirring up the bottom of lakes and accidentally eat lead fishing weights or spent lead shot pellets. Lead that is consumed breaks down in the stomach and is then transported through the blood. The lead is then absorbed into tissues, such as the liver, kidneys and bone.

Clinical signs

Birds exposed to sudden high levels of lead can die suddenly with no signs. Birds that suffer from slow longer-term exposure to lead can show signs of weakness, loss of muscle mass and fat reserves, green diarrhea, incoordination, paralysis or convulsions. Long-term effects of lead exposure can alter the behavior and survival of birds.

Disease management

In 1991, the US Fish and Wildlife Service launched a nationwide ban on lead shots for waterfowl hunting to reduce the number of lead shots falling into lakes. The Department has prohibited the use of lead shots for hunting mourning doves on state-managed lands since the inception of dove hunting in Wisconsin in 2003.

Hunters wanting to help reduce the loss of wildlife from lead toxicity can switch from using lead ammunition to non-toxic ammunition for all their hunting activities. People who fish can purchase non-lead fishing tackle and dispose of their lead tackle by taking it to a recycling facility that accepts and properly disposes of lead. Other wildlife enthusiasts can help by sharing information with their family and friends on the dangers of lead to wildlife.

Public health

Lead can accidentally be consumed by people when eating wild game that was harvested with lead ammunition. Deer harvested with lead bullets have been shown to have tiny lead fragments remaining in the processed meat which can be found far from the wound created by the bullet. These fragments are often too small to be seen, felt or noticed when eating the meat. While it has not been documented that lead fragments found in the wild game caused illness in humans, some precautions found in the link below are advisable.

Additional information

Mange

Mange is a skin disease that is caused by a microscopic mite. Several species of mange mites generally affect different species of animals. The most common type of mange in wildlife is sarcoptic mange, caused by the Sarcoptes scabiei mite. In Wisconsin, this mite has been documented in red foxes, coyotes and wolves. Gray squirrels in Wisconsin have been documented with mange caused by the Notoedres sp. mite.

Transmission

Transmission of the mite occurs between animals with close direct contact. Mites can survive in the environment and infested dens, burrows or nests can be a source of infection.

Clinical signs

Wildlife infected with mange mites will have hair loss and may be observed spending increased time scratching at their skin. Frequently with sarcoptic mange, a secondary bacterial infection will develop and the skin will become crusty with scabs. Animals with severe infections become emaciated and weak.

Disease management

In less severe cases, the wild animal’s immune system may be able to limit or eliminate the disease over time. Treating mange in wildlife can only be done legally by a licensed wildlife rehabilitator under controlled conditions to assure proper dosage and administration and adherence to all applicable state and federal laws governing the use of drugs in animals.

Public health

Sarcoptic mange mites can occasionally infect people. Clinical signs of mange in people include a localized, itchy red rash.

Additional information

Newcastle disease

Newcastle disease is a highly contagious disease of birds that is caused by a virus. There are many strains of the Newcastle disease virus (NDV) which are classified by the severity of the disease each causes in domestic poultry. In North American wild birds, large mortality events have been reported in double-crested cormorant breeding colonies as early as the 1990s. White pelicans and several species of gulls have also been affected.

In Wisconsin wild bird populations, periodic outbreaks of NDV have resulted in illness and death in breeding colonies of double-crested cormorants, generally occurring in early fall.

Transmission

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 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. Newcastle disease virus is capable of surviving in the environment and on objects such as shoes and clothing. Healthy birds can become infected after contact with contaminated objects.

Clinical signs

Signs of disease in birds vary from mild to severe depending on the strain of the virus. 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.

Disease management

Department staff routinely investigate when large numbers of sick or dead wild birds are reported. This is an effective tool for the detection of NDV outbreaks. Control of NDV in wild populations is difficult as large amounts of the virus are shed by infected birds, contaminating the surrounding environment.

The virus is fairly stable and can persist in the environment for long periods under the right conditions. Because the virus is highly contagious and of high risk to domestic poultry, it is important to identify the outbreak site as a contaminated area and follow precautions to prevent the disease from spreading to other areas. When an outbreak in wild birds is detected, care should be taken to limit contact between wild birds and domestic poultry.

If you find a group of dead birds, contact the DNR Wildlife Hotline by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff to return your call. In your message, please include the number of animals, the species (such as pelican), if they were sick or dead, the specific location where you saw them, including the county and your contact information.

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.
Rabbit hemorrhagic disease

For information on Rabbit, hemorrhage disease visits the Emerging Wildlife Diseases page.

Rabies

Rabies is a contagious, usually fatal disease of the central nervous system that is caused by a virus. All warm-blooded animals, including humans, are susceptible to rabies. Birds and reptiles are not susceptible to naturally-acquired rabies and do not pose a risk of transmitting it to humans. There are several strains or variants of the rabies virus based on the species of animal in which the virus circulates and is maintained. In Wisconsin, skunks and bats are the main rabies carriers.

Transmission

The virus is transmitted through scratches, bites or having the infected animal’s saliva contact with an open wound or mucous membrane.

Clinical signs

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.

Disease management

To reduce the spread of rabies in wildlife, the US Department of Agriculture established a National Rabies Management Program [exit DNR] that uses baits laced with vaccines that are directed at specific wildlife species in targeted areas in the eastern US and Texas. Vaccination of domestic animals, including farm animals, is the best method of protecting human health.

Public health

Observe and enjoy wildlife from a safe distance. Anyone who has been bitten, scratched or has come into contact with the 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. Then 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 Wisconsin Department 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 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 pet’s veterinarian and the Wisconsin Dept. of Ag, Division of Animal Health [exit DNR]. Dead wildlife carcasses may still harbor live rabies virus and could potentially infect pets that come into contact with them.

Additional information on rabies

Raccoon roundworm

The Raccoon roundworm, Baylisascaris procyonis, is an internal parasite of raccoons. The parasite lives in the intestinal tract of raccoons and generally does not harm the raccoon unless the raccoon is otherwise debilitated.

Transmission

Adult worms living in the intestines of raccoons release parasitic eggs in raccoon feces. The eggs may be found on the ground or in the surrounding vegetation. Eggs can survive in traps, caging or other enclosures used for captive raccoons. Other animals, especially woodchucks, rabbits and squirrels become infected by ingesting eggs from contaminated vegetation or other surfaces. 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 occasionally result in death.

Clinical signs

Raccoons may show no signs of having roundworms. In other wildlife, if the larvae migrate to the brain, signs may include a head tilt, walking in circles, falling over and seizures.

Disease management

Raccoon roundworms are very hardy and can only be killed by intense heat. The eggs do not become infective until 10-14 days after the raccoon defecates, so prompt clean-up of raccoon feces lessens the risk of exposure.

Public health

People can become infected by accidentally ingesting eggs from contaminated surfaces, including unwashed hands. Children are at the greatest risk because they tend to put their fingers in their mouths and play in areas where raccoons may have defecated. There is no reliably successful treatment to rid the roundworms in people.

Homeowners should take steps to discourage raccoons from visiting and nesting in areas used for personal recreation such as gardens and backyards, especially where children play. Raccoons tend to use “latrines” and any accumulated raccoon feces should be carefully removed and burned or buried. Gloves and a mask should be worn when handling raccoon fecal material or anything that may have been contaminated with raccoon feces.

Additional information

Salmonellosis

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.

Transmission

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 songbirds, such as pine siskins, common redpolls, and finches, during late winter and early spring when birds are stressed and congregate around bird feeders and birdbaths.

Clinical signs

Signs of salmonellosis vary greatly and are dependent on age, species, bacterial strain, and environmental stressors. Birds may show signs ranging from a gradual onset of disease to sudden death. Infected birds may appear "fluffed-up" and huddled together and maybe shivering. Many times, the first sign is finding multiple dead birds in a backyard where feeders are present.

Disease management

Salmonellosis does not contribute to a substantial population decline in wild bird species and is more of an interest to individuals who provide bird feeders and birdbaths. 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% 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 overcrowding 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 the feeder or birdbath, wash and disinfect it using the 10% bleach solution and wait at least a week before putting it back up. If possible, move it to a new location.

If you find a group of dead birds, contact the DNR Wildlife Hotline by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff to return your call. In your message, please include the number of animals, the species (such as house finch), if they were sick or dead, the specific location where you saw them, including the county and your contact information.

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, birdbaths and birdhouses.

Additional information

Severe Perkinsea infection of frog tadpoles

Severe Perkinsea infection (SPI) is an emerging disease of frogs and is the third most common infectious disease of frogs after chytridiomycosis (infection with chytrid fungus) and ranavirus. It was first detected in 1999 in New Hampshire with detections in several other states in subsequent years. It was first identified in Wisconsin as the cause of green frog tadpole mortality in Vilas County in the summer of 2017.

SPI is caused by a protozoan (single-celled) parasite in the phylum Perkinsea that infects and causes mass mortalities in tadpoles. So far it has not been associated with the mortality of adult frogs. Outbreaks can cause tadpole mortality rates as high as 95% and can reoccur at the same location for multiple years.

Transmission

The protozoan parasites produce spores that persist in harsh conditions and remain viable even when wet areas dry up. Once a tadpole is infected the organism spreads throughout the body causing damage to multiple internal organs.

Clinical signs

Infected tadpoles in Wisconsin were lethargic and observed swimming in circles and upside down. Other reported signs include enlargement of the body cavity and skin lesions/discoloration.

Disease management

Currently little is known about the transmission of this parasite. When sick or dead amphibians (tadpoles, salamanders, frogs) are observed, care should be taken to prevent potentially moving any infectious diseases to another location. At a minimum, rinse off footwear and either air dry in the sun for a few days, disinfect with a 10% bleach solution or wipe off with 70% alcohol wipes before wearing to another water area.

Public health

There is no known risk to people or pets.

Additional information

Snake fungal disease (SFD)

Snake fungal disease (SFD) is an emerging disease that impacts numerous species of snakes and has been found throughout much of the eastern United States. It is caused by a fungus, Ophidiomyces ophiodiicola, and can cause lumps along the snake’s face, neck and body. In other snakes, skin blisters or scabby areas may be the only sign of disease. Read more about SFD and report suspected signs of SFD here.

Squirrel pox

Squirrel pox, also called squirrel fibroma, is caused by a poxvirus called squirrel fibroma virus, which is related to other poxviruses. 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.

Transmission

Biting insects, such as mosquitos, are likely 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.

Disease management

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 mourning doves, purple finches, house finches and one peregrine falcon.

Transmission

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 adults regurgitate food for their offspring. Food and water sources, such as backyard bird feeders and birdbaths, can become contaminated from the mouths of infected birds. Raptors that prey on small birds, such as peregrine falcons, 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 becomes masses that eventually cause blockages within the mouth. Birds appear to have difficulty swallowing or breathing.

Disease management

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 trichomoniasis in wild birds includes reducing potential transmission to unaffected birds. When visibly affected birds are present, bird feeders and birdbaths 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". It is caused by a bacterium, Francisella tularensis. This bacterial disease is not common in Wisconsin but is most frequently found in Wisconsin muskrats, beaver, or rabbits.

Transmission

The bacteria are typically transmitted to wildlife through the bites of ectoparasites such as mites, ticks, flies, midges, black flies, fleas, mosquitoes and lice.

Clinical signs

There are generally very few signs associated with this disease in wildlife and they may only appear weak or slow-moving. Infected wild animals generally die quickly and will appear to be in good physical condition. They may have an enlarged spleen or liver covered with small white spots.

Disease management

This disease is not common in Wisconsin wildlife. When it is confirmed, the removal of carcasses to reduce the risk to humans is recommended.

Public health

This disease can be transmitted to humans by biting insects, direct contact with infected animals, inhaling the bacteria during landscaping activities or eating contaminated meat or water. People should use insect repellents to avoid insect bites, avoid handling or mowing over dead wildlife and avoid drinking untreated water. Hunters should wear gloves when cleaning the game and cook game meat to the recommended temperature.

Additional information

Tyzzer's disease (Clostridium piliforme)

Tyzzer's disease is a bacterial infection caused by the spore-forming bacterium, Clostridium piliforme. It is found in muskrats and cottontail rabbits.

Transmission

The likely method of transmission is through the ingestion of spores in the feces of infected wildlife.

Clinical signs

Infected wild animals may have bloody diarrhea and appear weak, but there are generally no signs observed. The disease kills infected wild animals quickly and wildlife is usually found dead appearing in good physical condition.

Disease management

Overpopulation, limited food resources and other stress factors may contribute to outbreaks of this disease. Management of populations at or near sustainable levels may help to deter outbreaks. The bacterial spores are long-lived in the environment. Management during outbreaks includes removal and proper disposal of carcasses and removal of infected muskrat lodges.

Public health

Tyzzer’s disease is not a risk for people.

Additional information

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.

Transmission

Female botflies 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 warble will have noticeable bumps or bumps under the skin. There may be an opening caused by the larva before leaving the body. Depending on the part of the body affected, the movement of the wild mammal may be hindered. Generally, infected individuals recover after the botfly 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.

Disease management

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 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.

Transmission

WNV is spread through the bite of infected mosquitos. The virus is maintained and replicates in certain species of birds. A mosquito becomes infected with the virus when it takes a blood meal from a bird with a circulating virus in its blood and then transmits the virus to another bird or mammal, including humans.

Clinical signs

Many species of birds can be infected with WNV without showing signs. However, corvid species (blue jays, crows, and ravens), some raptors (hawks and owls), and species of birds that have never been exposed to the virus can die from the infection. The infection can cause inflammation of the brain and heart. Signs of infection in birds may not appear until the last stage of the disease when the brain becomes inflamed. These signs may include tremors, head tilting, lethargy, loss of coordination, inability to fly or walk properly or trouble standing upright. Often, birds die suddenly after exhibiting no signs at all.

Disease management

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 by reducing or eliminating mosquito breeding habitats.

  • Eliminate stagnant water from your property.
  • Regularly clean birdbaths to remove the stagnant water and mosquito larvae.
  • Empty water-filled containers where mosquitoes may breed.

If you find a group of dead birds, contact the DNR Wildlife Hotline by emailing DNRWildlifeSwitchboard@wisconsin.gov or calling 608-267-0866. You will need to leave a message for the hotline staff to return your call. In your message, please include the number of animals, the species (such as crow), if they were sick or dead, the specific location where you saw them, including the county and your contact information.

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 mild, flu-like disease. In some cases, usually among the elderly, WNV causes a serious disease that affects the brain tissue and can be 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 on the Wisconsin Department of Health website [exit DNR].

Additional information

White-nose syndrome in bats

White-nose syndrome (WNS) is a disease of bats that hibernate in caves, mines, and other suitable hibernacula. It is caused by the fungus Pseudogymnoascus destructans (Pd). It was first identified in North America in 2007 in bats in a cave in New York. The fungus gradually spread across the United States and was eventually discovered in Wisconsin bats in 2014. All four of Wisconsin’s cave bats – tricolored bat, northern long-eared bat, big brown bat, little brown bat – are susceptible to Pd fungal infection. Additionally, they are two tree bat species in Wisconsin on which Pd has been detected, but no diagnostic sign of WNS has been documented: silver-haired bat and eastern red bat.

Transmission

The fungus thrives in cold, dark damp caves where bats hibernate and overwinter. It spreads from bat to bat or onto bats that touch contaminated surfaces. The fungus survives a long time on shoes, clothes and other gear and people can unknowingly move it to new areas.

Clinical signs

Hibernating bats will have a visible fuzzy white growth on the face or wings. The fungus causes changes in the bats that cause them to be abnormally active in the winter, including flying outside the cave in cold weather. This makes the bats use up the stored fat that they need to survive the winter. Infected bats lose weight and become dehydrated. The fungus can also cause damage to its wings.

Disease management

There is currently no known treatment for the disease. Management focuses on preventing or minimizing the spread of the fungus. Visitors to caves and mines where bats hibernate are restricted or limited. Wisconsin has Decontamination Protocols for Preventing the Spread of White-Nose Syndrome in Bats [PDF]. Many organizations and agencies are researching to find a treatment, including vaccine trials. Citizens can help by reporting sick or dead bats to the WDNR's Wisconsin Bat Program.

Public health

The fungus does not infect people or pets.

Additional information

White-nose Syndrome Response Team: current map of the occurrence of WNS [exit DNR]
USGS National Wildlife Health Center: White-nose Syndrome [exit DNR]
More information on bats in Wisconsin can be found on the department’s webpage: Saving Wisconsin's Bats
Wisconsin River Bald Eagle syndrome

Wisconsin River Bald Eagle syndrome is a name given to a specific group of signs which have consistently been found in sick or dead bald eagles in certain locations in Wisconsin, but for which a specific cause of those signs has not yet been found.

During the winter of 1994-95, 14 bald eagles were found sick or dead along the lower Wisconsin River in Sauk and Columbia Counties. Thirteen sick or dead bald eagles were found during the winter of 2000-2001 and the area had expanded to include Dane and Adams Counties. Fewer eagles with specific signs and lesions for this syndrome were identified in the subsequent years. However, in 2017, five bald eagles were found dead along the Fox River and Little Lake Butte des Morts in Winnebago, Outagamie and Calumet counties and one bald eagle found dead along the Branch River in Manitowoc county was determined to have died from this syndrome.

Extensive diagnostic testing for bacteria, fungi, viruses, parasites, and contaminants has not yet identified the cause. DNR staff continue to monitor bald eagles for this syndrome.

Transmission

The cause and transmission of this syndrome are unknown.

Clinical signs

Sick eagles are weak and show signs of neurological disease including incoordination, tremors and seizures. At necropsy, all the eagles have abnormal spaces in the cytoplasm of cells of the liver when observed under the microscope (microscopic hepatocellular cytoplasmic vacuolation). Some eagles also have microscopic lesions in the brain.

Disease management

Because the cause of the syndrome is unknown, there are no management actions to take at this time.

Public health

There is no evidence to suggest this syndrome affects people.

Additional information

Winter Mortality of Bald Eagles Along the Lower Wisconsin River, Mclaughlin, et al., 2004 Proceedings AAZV, AAWV, WDA Joint Conference, pages 312-313 [PDF exit DNR]