A mysterious disorder that in recent years has killed at least 25 bald eagles along Thurmond Lake's wooded shorelines appears unlikely to affect mammals, according to new research.
The eagles - and unknown numbers of Canada geese, coots and at least one great horned owl - succumbed to avian vacuolar myelinopathy, or AVM - an always-fatal condition whose origins remain a mystery.
Scientists have studied AVM since it first appeared in Arkansas in 1994, but efforts to unravel its origins have been unsuccessful. The disorder causes spongelike brain lesions that kill affected animals.
Earlier this year, the Southeastern Cooperative Wildlife Disease Study at the University of Georgia's School of Veterinary Medicine conducted studies in which AVM-affected birds were fed to pigs.
The idea, according to data posted on the center's Web site, was to see whether the pigs developed the fatal brain lesions. None did.
"Results of this trial indicate that young pigs do not develop central nervous system lesions within one month of consuming affected tissues," the summary said.
Although the results are good news, especially for hunters who eat waterfowl harvested in areas known to harbor AVM, researchers warn that the experiment is by no means conclusive.
"You could say it's definitive, but just for pigs," said Dr. Tonie Rocke, an epizootiologist at the National Wildlife Health Center in Madison, Wis., which also is studying AVM.
"It means there is still no evidence it affects mammals, but I'd be hesitant to jump to any broad conclusions based on these experiments alone," she said.
The condition is believed to be linked somehow to hydrilla, an invasive aquatic weed that found its way into Thurmond Lake about the same time eagles began dying along its shores.
"We believe it's somehow associated with hydrilla but not the hydrilla itself," Dr. Rocke said. "We suspect it's some kind of agent, or toxin - not an infectious disease, but probably a microbial bacteria or algae that produces a toxin."
It is possible that AVM stems from algae ingested by coots that in turn are consumed by eagles and birds of prey.
So far this year, relatively few cases of AVM have been found, she said. "It's a very mild year so far, but we know things could change as we get into the colder months."
Other participants in AVM studies include the Army Corps of Engineers, U.S. Fish & Wildlife Service, Clemson University and departments of natural resources in South Carolina and Georgia.
Bald eagle nesting expanded across much of Georgia last year, but declined in the Thurmond Lake area, where only two occupied nests were found, compared to an average of nine.
Reach Robert Pavey at (706) 868-1222, Ext. 119, or rpavey@augustachronicle.com.
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