Mysterious Bald Eagle Killer Identified After 25 Years

The animals lose control over their bodies and holes form in their brains as a result of the disease.
Derya Ozdemir
A bald eagle flyingKenCanning/iStock

For some 25 years, bald eagles, Haliaeetus leucocephalus, have been dying on a mass scale because of a mysterious disease at lakes across the United States. The disease's effects are gruesome: the animals have no control over their bodies and holes form in their brains.

It's estimated that at least 130 eagles have died of VM, but the real number is probably at least 10 times that number. Bald eagles are not the only species that are affected by the disease. Fish, frogs, snails, salamanders, turtles, snakes, owl, and waterfowl are all affected; however, since bald eagles feed on all of those other infected animals, they are one of the most affected.

Earl on, a previously unknown neurodegenerative disease with an unknown origin called vacuolar myelinopathy (VM) was identified. Now, a new research, published in Science, by the Martin Luther University Halle-Wittenberg (MLU) in Germany and the University of Georgia, USA, has found the culprit behind the deaths: a neurotoxin called aetokthonotoxin.

A nearly 30-year hunt

At first, scientists had no idea where the eagles got the disease from, but an invasive plant and a particular species of cyanobacteria were found to be responsible, Live Science reports. It was seen that VM was found only in lakes where an invasive plant species, Hydrilla verticillata, was also found; however, a direct link couldn't be formed since not all lakes where Hydrilla verticillata grows were linked to VM.

A new study conducted in 2015 identified a species of cyanobacteria (Aetokthonos hydrillicola) that was found on Hydrilla verticillata in lakes where VM was plaguing animals. However, the scientists still didn't have an answer for how the bacteria were causing VM and didn't know the exact mechanism behind the disease.

This new study points at aetokthonotoxin which is produced under particular circumstances by the cyanobacteria living on the invasive plants. The scientists sent samples of the cyanobacteria to the researchers in Germany and they attempted to grow cultures of the bacteria and see what toxins they produced.

At first, cyanobacteria grown in usual cultures did not produce any toxin. However, when grown on cultures that included bromide, cyanobacteria produced aetokthonotoxin that researchers now think causes VM. Bromide occurs naturally in lakes in small doses, but there is human interference as well. Humans introduce bromide to lakes in the form of herbicides, ironically, to control the spread of the invasive plant. 

Scientists are yet to know why cyanobacteria produce the toxin and why they only do so in the presence of bromide. They are hoping to better understand the toxin responsible for VM and find ways of managing it. 

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