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
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:
- Continue to monitor AVM at lakes where the disease occurs and at nearby lakes without disease.
- 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.
- Identify the causative agent of AVM.
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Bald Eagle with AVM
Photo by Ron Parker - FWS
USGS AVM Resources