Disease threatens bald eagle population

Bald eagles affected by the disease can have trouble flying, walking, or swimming

ATLANTA, Georgia (CNN) -- The burgeoning bald eagle population is threatened by a mysterious disease that has killed more than 80 of the majestic birds over the last six years. Scientists have yet to discover how the eagles are contracting it.

Avian vacuolar myelinopathy, or VM, causes lesions in the white matter of the brain and spinal cord of affected birds, according to the Avian Vacuolar Myelinopathy Interagency Web site. As a result, the afflicted birds may have trouble flying, walking or swimming.

The disease also is starting to appear in other birds, including coots and other waterfowl.

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"We're speculating that maybe it's being passed to the eagles through the coots, which is one of their food supplies," said Jim Ozier, of the Georgia Department of Natural Resources.

Researchers are conducting autopsies of the dead eagles to search for clues.

"Well, the diagnosis work so far has not found any evidence of bacteria, virus or parasites," said John Fischer, University of Georgia veterinary researcher. "That kind of leaves us with the possibility of some type of compound, either natural or manmade, that's in the environment that might be causing the problem."

Eagles build their nests on top of trees near rivers and lakes, where pesticide runoff can be a problem

A toxic algae bloom is one possibility, authorities said. Eagles build their nests atop trees near rivers, lakes and the ocean because that's where their food -- fish and waterfowl -- comes from.

Over the last three decades, bald eagles have made a remarkable recovery in the lower 48 United States, thanks in large part to the Endangered Species Act, which protects them and their habitat.

Only about 450 nesting pairs of bald eagles existed in the 1960s. Many of the eagles had been killed off by the pesticide DDT, which was banned in 1972. Now there are around 4,500 nesting pairs.

CNN Correspondent Brian Cabell contributed to this report.

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Avian Vacuolar Myelinopathy Interagency

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