- The mysterious brain disease responsible
for the deaths of bald eagles and American coots in Arkansas has now been
found in two species of ducks discovered dead at Woodlake, North Carolina,
and in bald eagles and coots from three other southeastern states. According
to a USGS wildlife disease specialist, this is the first time the new disease,
called avian vacuolar myelinopathy, has been documented in species other
than American coots and bald eagles.
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- Pathologists at USGS's National Wildlife
Health Center in Madison, Wisconsin, and the Southeastern Cooperative Wildlife
Disease Study (SCWDS) at the University of Georgia have confirmed that
bald eagles collected from four new locations (near Woodlake, North Carolina;
Aiken, South Carolina; and Strom Thurmond Lake and Lake Juliette, Georgia)
and coots from Aiken, South Carolina, died from the same brain disease
that has killed at least 58 bald eagles in Arkansas and an unknown number
of coots in Arkansas, North Carolina and Georgia.
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- The disease affects the brain and spinal
cord by damaging the myelin sheath that insulates the nerve fibers. It
is diagnosed by microscopic examination of very fresh brain and spinal
cord tissue. Dr. Nancy Thomas, the USGS pathologist who first described
the lesion, explained that "In affected birds the disease appears
as open spaces in the white matter of the brain." When the coating
surrounding the myelin is damaged, Thomas said, "Communication in
the nervous system is impaired, causing a bird to become uncoordinated
or paralyzed." Thomas used an electron microscope to determine that
the spaces are caused by separation of the myelin layers that surround
nerve fibers. Using the same techniques, Dr. John Fisher, a SCWDS pathologist,
confirmed the lesion in a North Carolina mallard and ringnecked duck, and
a Strom Thurmond Lake bald eagle.
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- USGS wildlife disease specialist Dr.
Kimberli Miller said that afflicted birds typically fly erratically or
are unable to fly; they may crash land, swim tipped to one side with one
or both legs or wings extended, or be in the water on their backs with
their feet in the air. "On land," said Miller, "birds appear
intoxicated - they stagger and have difficulty walking and may fall over
and be unable to right themselves." Affected birds, however, are usually
alert and still may bite when handled.
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- Miller said that the only consistent
finding in affected birds is the microscopic change in the nervous system.
Despite extensive testing by USGS, SCWDS, and others, the cause of the
disease and the route of exposure is still unknown. "All of the diagnostic,
field and laboratory efforts indicate the cause is most likely a toxin,
either one that is naturally occurring or manmade," Miller said. In
addition to toxicology tests, USGS pathologists have tested the tissues
of dead birds for bacteria, viruses, and parasites and none have been found.
In humans and other mammals, similar lesions have been associated with
genetic disorders, certain types of chemicals or toxic plants. Tests for
these chemicals in the affected birds have been negative or inconclusive.
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- "This is very frustrating for our
scientists," said Dr. Robert McLean, director of the USGS National
Wildlife Health Center. "We have examined more than 4,000 bald eagle
carcasses from around the country to determine the cause of death, and
have conducted thousands of wildlife mortality investigations on many other
species, and we are accustomed to identifying and resolving these problems.
With this disease, however, despite all our efforts and despite the extensive
involvement of leading scientists from diverse disciplines and numerous
organizations, we have yet to solve the puzzle about the exact cause of
the disease."
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- McLean noted that "vexing"
questions about the disease still need to be answered. He asked: "Is
it emerging and spreading to new locations and new species, or has it been
around for a long time and just now being recognized because more people
are aware of the problem? If it is an emerging disease, finding out what
is causing it may be just the tip of the iceberg."
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- USGS and SCWDS recently issued a joint
Wildlife Health Alert informing wildlife biologists and public land managers
of the problem and requesting that they report observations of birds exhibiting
wobbly, uncoordinated flight or impaired swimming ability to Wildlife Disease
Specialists at NWHC or SCWDS. Additional information can be found at http://www.emtc.usgs.gov/http_data/nwhc/news/news.html
.
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- As the nation's largest water, earth
and biological science and civilian mapping agency, the USGS works in cooperation
with more than 2000 organizations across the country to provide reliable,
impartial, scientific information to resource managers, planners, and other
customers. This information is gathered in every state by USGS scientists
to minimize the loss of life and property from natural disasters, contribute
to the sound conservation, economic and physical development of the nation's
natural resources, and enhance the quality of life by monitoring water,
biological, energy, and mineral resources.
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