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Secret Behind the Mysterious Disease That Is Killing Bald Eagles


ATHENS, GEORGIA — Scientists have discovered the cause of a mysterious illness that turns bald eagles into zombies before they die, according to a paper published in the journal Science.

In 1994, dozens of bald eagles died in Arkansas. Before they died, they displayed signs of neurological impairment including crashing into objects such as trees and cliffs. Necropsies found these birds had distinct lesions and holes that made their brains look like sponges, as if they had been eaten from the inside.

Eventually, it was determined that these bald eagles — and in the ensuing years dozens of others from Texas to the Carolinas — had caught the illness from the waterbirds they preyed on that often displayed similar zombie-like behavior.

The condition is known as avian vacuolar myelinopathy, or AVM. Lab analysis showed that the eagles’ prey had ingested large amounts of the invasive plant Hydrilla verticillata, also known as water-thyme.

By 2014 researchers at the University of Georgia had shown that a species of cyanobacteria that grows on the plant was responsible for AVM. They named the bacteria Aetokthonos hydrillicola, or “eagle killer” that “lives on hydrilla.” However, when researchers fed eagles lab-grown A. hydrillicola, the eagles did not get sick.

Now, in a new study published in the journal Science, scientists at the University of Georgia, Germany and the Czech Republic have identified the source of the neurotoxin. The bacteria only produce it when they come into contact with bromide.

In their paper the researchers say further investigation is needed to determine where the bromine is coming from. But there are some clues. All of the lakes where the eagles of AVM died were man-made. And bromide is found in some herbicides used to control infestations Hydrilla verticillata.

SOURCES: New Scientist, Science, National Library of Medicine

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