For the last 25 years, a mysterious ailment has been killing bald eagles in the US and leaving them with holes in their brains. Researchers identified vacuolar myelinopathy (VM), a deadly condition that brings on paralysis, blindness, and seizures in bald eagles and their prey, including fish, turtles, snakes, and smaller birds—and now they think they know what caused it, per Live Science. Initial suspicions fell on Hydrilla verticillata, a highly invasive plant native to Central Africa and common in fish tanks, which has been taking over lakes in several states. As only some of those lakes were linked to VM, later research pinpointed a species of cyanobacteria found on certain Hydrilla plants. In a lab setting, the cyanobacteria cultures failed to produce any toxin whatsoever. That changed, though, when researchers added bromide to the mix, per a release.
The bacteria produced the toxin dubbed aetokthonotoxin, or "poison that kills the eagle." Bromide occurs naturally in small quantities in lakes but is also introduced through chemical run-off and herbicides, which are "ironically used to control the spread of Hydrilla," per Live Science. Further research showed the plant is "able to enrich bromide from the environment, making it even more available to the cyanobacteria," per Wired. "It was only this discovery that made us aware that VM is also spreading due to [human] influence," says Steffen Breinlinger, who worked with an international team of researchers on a study in Science. He notes VM may never be eradicated from US lakes, but "if we control the bromide in the reservoirs ... ultimately [the cyanobacteria] will be stripped of its weapon." Wired notes that the effect on humans who eat infected animals is not yet clear. (Read some much better news for bald eagles.)