National Wildlife Health Center

...advancing wildlife and ecosystem health

Avian Vacuolar Myelinopathy


Avian vacuolar myelinopathy (AVM) is a recently discovered neurological disease affecting waterbirds, primarily bald eagles and American coots, in the southern U.S. At least 80 bald eagles and possibly thousands of American coots have died from AVM since it was discovered in 1994 at DeGray Lake, Arkansas. AVM has also been confirmed as the cause of death in mallards, buffleheads, ring-necked ducks, Canada geese, killdeer, and a great horned owl.

Birds affected with AVM lack muscle coordination and therefore have difficulty flying and swimming. Birds that died from AVM generally appeared to be in good health with the exception of a characteristic lesion in the myelin of the brain and spinal cord. Thorough necropsy and diagnostic laboratory studies at the USGS National Wildlife Health Center (NWHC) produced no evidence of parasitic, viral, bacterial, or prion infections. Natural or man-made toxins are suspected as the most likely cause of AVM based on histopathological findings. A sentinel study demonstrated that exposure to the agent that causes AVM is site-specific, seasonal, and relatively short in duration. Feeding trials performed at the NWHC with plant material collected from one of the lakes during an outbreak demonstrated that the causative agent of AVM is associated with submersed aquatic vegetation and that the onset of AVM is dose-dependent.

Future collaborative research with the Southeastern Cooperative Wildlife Disease Study, U.S. Fish and Wildlife Service, and Wright State University has three objectives:
  1. Continue to monitor AVM at lakes where the disease occurs and at nearby lakes without disease.
  2. Characterize environmental factors at the sites where AVM has occurred. These site characterizations will be instrumental for developing risk assessment models and may generate hypotheses regarding environmental conditions conducive for AVM outbreaks.
  3. Identify the causative agent of AVM.

For more information on Avian Vacuolar Myelinopathy, please use the Contact Form

Bald Eagle with AVM
Bald Eagle with AVM
Photo by Ron Parker - FWS


USGS AVM Resources
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AVM Wildlife Health Bulletins
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Page Last Modified: Dec 31, 2013