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For information on wildlife health, contact:
Nancy Businga
Wildlife health lab manager
Bureau of Wildlife Management
608-221-5375

Bird diseases

The following are short summaries of some diseases that are more commonly thought of being associated with birds. However for some of these diseases additional groups such as mammals (including humans) can also be affected.

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.

Transmission

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.

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.
Reporting

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.

Salmonella

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 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 bird baths. 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% 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 bird baths regularly.
  • If a sick or dead bird is found near a feeder or bird bath, remove it, clean it using the 10% bleach and wait at least a week before putting it back up. If possible, move it to a new location.

Newcastle

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

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.

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 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

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

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.

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.

Avian Influenza

Fall migration
In wild birds, infections with avian influenza viruses typically increase during pre-migration staging, when large numbers of birds concentrate in one area.

Avian influenza (AI) is a viral disease 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 or have the ability to infect animals other than birds.

In rare instances, there have been mortalities of wild and domestic birds by AI viruses. The best known is caused by the highly pathogenic H5N1, or "bird flu" viral subtype, which has been detected in Asia, Europe and Africa. This strain has not been detected in Wisconsin or North America, nor have there been large mortality events from AI viruses in North America.

Transmision

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.

Public health

The majority of AI viruses do not infect humans. There are a few subtypes that do have the ability to infect other animals and humans, including the highly pathogenic H5N1, or "bird flu", virus.

There are simple precautions to take to minimize risk of infections.

  • 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 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.

Wildlife management

From 2006 - 2010 the Department of Natural Resources (DNR) along with the U.S. Department of Agriculture, actively tested 6,176 wild birds for exposure to AI viruses through the national Highly Pathogenic H5N1 surveillance program. Of those, a total of 1,084 (17.55%) wild birds tested positive with a subtype of AI in Wisconsin. However, none of the viral subtypes detected were the highly pathogenic H5N1 virus, and the majority do not cause signs disease or mortality in wild birds or are currently known to infect other animals, including humans.

Currently, the DNR does not actively test wild birds for AI viruses. However, when wild birds are submitted for diagnostic evaluation, Wildlife Health staff will test for AI if appropriate. Additionally, the U.S. Department of Agriculture and the U.S. Department of the Interior along with the DNR do routinely investigate mortality events when large numbers of birds are involved. Investigating sick or dead wild bird events is an effective tool for early detection of AI outbreaks. In Wisconsin, if you find sick or dead birds, contact the dead bird hotline at 1-800-433-1610.

Active avian influenza surveillance in Wisconsin 2006 - 2010

Table 1: From 2006 - 2010, research scientists at the Wisconsin DNR actively tested wild birds in Wisconsin for avian influenza viruses. Of those found positive, none were of the HP H5N1 subtype.
Year Total # animals tested Total # animals positive Percent positive
2006 1266 101 7.97%
2007 498 47 9.44%
2008 502 109 21.71%
2009 2374 462 19.46%
2010 1536 365 23.76%
Totals 6176 1084 17.55%
Last revised: Monday June 09 2014