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Mysterious Disease Killing Birds in Several Southern States

Date Posted: September 8, 2000

Avian Vacuolar Myelinopathy (AVM), formerly known as Coot and Eagle Brain Lesion Syndrome (CEBLS) and Avian Brain Lesion Syndrome (ABLS), is a disease in birds that is thought to be caused by a neurotoxin (a toxin that damages or destroys nerve tissue) of unknown origin. The disease causes lesions (open spaces), or vacuoles, in the white matter of the brain and in the spinal cord of affected birds. Water birds with AVM often exhibit a reluctance to fly, erratic flight, or an inability to fly. Eagles have been observed flying into trees and rock ledges. While swimming, birds often appear to be partially paralyzed on one side of the body, resulting in the bird swimming with one leg extended, swimming in circles, or swimming upside down. On the ground, waterfowl and eagles stumble and wobble. However, signs of impairment are not always visible. Studies have found AVM lesions in coots that appeared to be behaving normally. Sick or dead birds affected by AVM are usually found between October and March.

A naturally occurring or manmade toxin is the most probable cause of the lesions. Tests for a wide range of known toxins such as pesticides and heavy metals have resulted in no significant findings. There has also been no evidence of infectious disease caused by viruses, bacteria or a prion related disease, like mad cow disease.

AVM was initially confirmed in Bald eagles (Haliaeetus leucocephalus) and in American coots (Fulica americana) by the US Geological Survey National Wildlife Health Center (USGS NWHC) in the fall and winter of 1994. In Arkansas in 1994, 29 bald eagles were found dead during the fall and winter at DeGray Lake in southwestern Arkansas. Another significant eagle die-off occurred at DeGray and at two nearby Arkansas lakes in the winter of 1996-97 when 26 eagles and numerous coots died. Since then, birds with AVM have also been documented in Georgia, North and South Carolina. In the winter of 1998-99, AVM was detected in waterfowl. This included small numbers of mallards (Anas platyrhynchos) and ring-necked ducks (Aythya collaris). Lesions consistent with the disease were also found in Bufflehead (Bucephala albeola) and American Wigeon (Anas americana) ducks.

During the winter of 1999-2000, AVM was confirmed in three eagles from Lake Ouachita, Arkansas; one eagle from Lake Greeson, Arkansas; and in American coots from Surf Lake (Woodlake), North Carolina, DeGray Lake and Lake Ouachita, Arkansas. While accurate coot counts are hampered by natural factors, such as large populations of predators and scavengers at lakes, it is estimated that a few hundred coots die from AVM annually. Bufflehead and wigeon ducks from North Carolina may have also been affected by AVM in 1999. Records research conducted in 1999 revealed that AVM may have occurred in North Carolina as early as 1990.

Several agencies and organizations have been working together in an effort to organize, coordinate and focus efforts to investigate and monitor the disease. The Service’s Southeast Region Environmental Contaminants Program Coordinator, Dr. Allen Robison, has been designated to coordinate these efforts. State and local agencies, other federal agencies, universities, and various other interested parties are important partners in this effort. Additional information on AVM will be posted on the Service’s Division of Environmental Contaminants web site as it becomes available.

If anyone has additional information, or suspects that AVM may be affecting birds in their area please contact the National Wildlife Health Center at (608)270-2448.

Service Contact: Dr. Allen Robison, (404)679-7127.

Last updated: June 12, 2015