National Wildlife Health Center

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Wildlife Health Bulletin #99-01


To: Natural Resource/Conservation Managers
From: Director, USGS National Wildlife Health Center (Bob McLean)
Title: NEUROLOGIC DISEASE IN NEW WILD BIRD SPECIES AND LOCATIONS
Date: February 8, 1999

Pathologists at the USGS National Wildlife Health Center (NWHC) in Madison, Wisconsin and the Southeastern Cooperative Wildlife Disease Study (SCWDS) at the University of Georgia have found changes in the brains of mallard, wigeon and ringed-necked ducks from Woodlake, North Carolina that are similar to the changes found in the brains of American coots and bald eagles with vacuolar myelinopathy. The disease had not previously been documented in species other than American coots and bald eagles. In addition, bald eagles collected from 4 new locations (near Woodlake, North Carolina; Aiken, South Carolina; and Strom Thurmond Lake and Lake Juliette, Georgia) and coots from Aiken, South Carolina appear to also have the same brain disease. In Arkansas, at least 58 bald eagles and an unknown number of coots have died from this disease since it was first detected in 1994. A previous Wildlife Health Alert confirmed vacuolar myelinopathy in coots collected at Woodlake in North Carolina and Lake Juliette in Georgia (See Wildlife Health Alert 98-03).

Vacuolar myelinopathy is a central nervous system lesion, diagnosed by microscopic examination of very fresh brain tissue. In affected birds it appears as open spaces in the white matter of the brain. Using electron microscopy, scientists determined the spaces are caused by separation of the myelin layers that surround and protect the nerves. Using electron microscopy, the SCWDS pathologist has confirmed the lesion in one of the North Carolina mallards and the Strom Thurmond Lake eagle. Electron microscopy confirmation of vacuolar myelinopathy lesions in the remaining ducks and eagles is pending.

Affected birds have erratic flight or are unable to fly, may crash land, swim tipped to one side with one or both legs or wings extended or be in the water on their back with their feet in the air. On land, birds stagger and have difficulty walking and may fall over unable to right themselves (appear intoxicated). Birds are usually alert and may bite when handled even if unable to escape capture. It remains unknown if the disease is "spreading" or if affected birds at other locations are recognized because more people are aware of the problem.

All diagnostic, field and laboratory efforts indicate the cause is most likely a toxin, either one that is naturally occurring or manmade. Tests have been unfruitful for the toxins previously associated with vacuolar myelinopathy in other species. Route of exposure to the toxin is not known at this time. Multiple agencies are continuing field, laboratory and research efforts to determine the cause of the disease.

Wildlife managers are encouraged to observe coots, waterfowl and eagles and report any sick birds to the National Wildlife Health Center at 608-270-2400 or the Southeastern Cooperative Wildlife Disease Study at 706-542-1741. If any freshly dead birds are found, please keep carcasses chilled on ice or refrigerated, but not frozen, while you contact the above agencies.

For further information and to report sick or dead crows or unusual bird mortality, please contact USGS, Wildlife Disease Specialists Linda Glaser (608-270-2446, ) or Kathryn Converse (608-270-2445).

 

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