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Common waterfowl afflictions
Sarcocystosis (commonly called Rice Grain Disease) is a disease of waterfowl caused by the protozoan parasite Sarcocystis rileyi. In Michigan, this disease is primarily observed in mallards and black ducks. The sarcocyst appears as a white cyst in the musculature of the breast and legs and can vary in number from a few to hundreds. The disease does not affect infected birds. Infected ducks are aesthetically displeasing and, even though it is unlikely humans could be infected by ingesting the cysts, it is recommended that the carcass be disposed of and not consumed.
Abscesses are commonly observed in waterfowl as a result of a traumatic injury, usually either a blunt trauma or trauma caused by a firearm projectile. Abscesses in avian species can be irregularly shaped, tan, white, gray, or black in color and solid, consisting of caseous necrotic (onion-like) material enclosed in a capsule. Often the breast musculature is the affected area. An abscess can easily be removed and the remainder of the carcass is edible.
Recent traumatic injuries can be observed in waterfowl that have either suffered blunt trauma or trauma caused by a projectile. Muscle tissue damage and subcutaneous and intramuscular hemorrhages are commonly seen in these instances. Areas of the musculature that contain blood can be trimmed and the remaining tissue is edible.
Lungs and airsacs
Aspergillosis is a respiratory disease of waterfowl caused by the fungus, Aspergillus fumigatus. Spores of this fungus exist in moldy bedding, vegetation, and feed where they are inhaled while the bird is resting or feeding. The spores lodge in the airsacs and lungs and form lesions. The airsacs can become completely lined with small to extensive yellow-white or tan flattened plaques. The membrane on the airsacs will also exhibit white, green, gray, or black mold growth. The lungs exhibit yellow-white or tan caseous necrotic foci surrounded by congested tissue. If lesions are noticed in the airsacs or lungs dispose of the carcass immediately. Humans are susceptible to this fungal disease.
Avian Influenza (AI) is a virus which can infect and be carried by migrating waterfowl and domestic poultry. AI viruses are classified as either low or high pathogenicity based on the ability of the virus to cause disease in domestic poultry. Low pathogenicity strains occur naturally in wild birds without causing illness. Wild birds with high pathogenicity strains rarely show signs of illness, but some wild birds will show neurological symptoms. In June 2015, geese in Macomb County showing neurological symptoms tested positive for a high pathogenicity strain, H5N2. In 2022, an outbreak of HPAI, strain H5N1, broke out across the globe. In Michigan, ~170 birds tested positive.
Lead poisoning in waterfowl is an infrequent cause of death in Michigan since the Fish and Wildlife Service required the use of non-toxic shot for waterfowl hunting in the United States starting in 1991. Occasionally we still see cases of the disease and it can occur in either an acute or a chronic nature. Lead poisoning causes muscle paralysis and death. In acute cases, large quantities of lead shot are ingested, resulting in high levels of lead in the tissues in a short time. These birds are in good to very good physical condition. In chronic cases, smaller numbers of lead shot are ingested and the bird dies over an extended period of time. These birds become emaciated as the digestive system fails to function. The birds continue to feed but are unable to obtain nutrition and develop food impactions in the esophagus and the gizzard.
West Nile Virus (WNV)
Waterfowl affected with West Nile Virus generally display neurologically abnormal behavior such as an inability to fly, walking or swimming in circles, or exhibiting a lack of fear of humans. Hunters may observe these birds when in the marsh or field and alert you of the bird’s behavior. The entire carcass of these birds should be collected and submitted for exam.