Since 2001, hundreds of bald eagles have been found dead near lakes in Arkansas. Their deaths, and later the deaths of other waterfowl, amphibians and fish, were the result of a neurological disease that led to the formation of cavities in the white matter of their brain. Now scientists have discovered that it has been killing bald eagles for over 20 years.
Field and laboratory studies over the past 20 years have revealed the main clues to wildlife: the death of eagles and waterfowl occurs in late autumn and winter in reservoirs with excess invasive aquatic weeds, and birds can die within five days after arriving at such a lake.
But until recently, the toxin that caused the disease, vacuolar myelinopathy, was unknown. Now, after years spent identifying a new toxic blue-green species of algae (cyanobacteria) and isolating the toxic compound, scientists have confirmed the structure of this toxin.
Cyanobacteria grow on the leaves of the invasive aquatic plant Hydrilla verticillata under certain conditions: in artificial lakes when bromide is present. Bacteria and animal deaths from the disease they cause have been reported in watersheds in the southeastern United States. This is why it is important for anyone outdoors, anglers, hunters, bird watchers and more, to be aware of the signs of this neurological infection and to avoid eating infected animals.
Scientists want people to recognize this disease before taking birds or fish from these lakes. In some animals – such as birds, turtles, salamanders and even beavers – the disease manifests itself in the form of erratic movements or seizures. However, anglers should be even more careful as it is impossible to detect a toxin in fish without obvious symptoms.
“I would not eat fish with damage or any deformities; scientists and researchers see the affected fish swimming slowly, but anglers will not be able to see it. We want people to know the lakes in which this disease has been registered and to be careful when eating birds and fish from them.”
Susan Wilde, Assistant Professor in the Department of Aquatic Sciences at the Warnell School of Forestry and Natural Resources
Researchers studying cyanobacteria have mapped and listed the watersheds affected. Now scientists have mapped the genome of bacteria to understand how they develop and survive. Scientists have been studying cyanobacteria since 2001, when bald eagles began to die in Georgia, South Carolina and North Carolina. In the following decades, the cyanobacteria themselves were discovered, called Aetokthonos hydrillicola (Latin for the killer eagle that grows on the hydrill), and links were established between invasive aquatic plants and the animals that eat them. But until recently, the origin of this brain-damaging disease remained a mystery.
Hydrilla samples collected in the field were then cultured in the laboratory and tested. But the tests were negative: the cyanobacteria from the laboratory did not cause the disease.
The scientists then used a new imaging mass spectrometer to examine the composition on the leaf surface of the plant, molecule by molecule. They discovered a new substance that is found only on leaves that grow cyanobacteria, but is not produced in cyanobacterial cultures. His research into the chemical structure of an isolated molecule revealed five bromine atoms.
“These properties are unusual for a molecule formed by cyanobacteria, and they explain why the toxin did not form in a bromide-free laboratory environment. Then we added bromide to our laboratory cultures and the cyanobacteria began to produce the toxin.”
Steffen Breinlinger, one of the researchers.
After nearly a decade of testing the isolated molecule and collaborating between laboratories, it turned out that this molecule actually causes vacuolar myelinopathy. The researchers call their discovery etoctonotoxin, “eagle-killing poison.”
Neurological disease has not yet appeared in Europe and no cases of toxin-forming cyanobacteria have been reported. It is not yet known that humans suffer from vacuolar myelinopathy, although researchers have successfully treated chickens with the toxin, and scientists now continue to test fish and waterfowl such as ducks and coots for the disease.