Killer Toxin That Turned Eagles' Brains Into "Swiss Cheese" Discovered After 30 Year Search

When a large number of individuals begin presenting with similar symptoms, scientists can find themselves battling an anonymous illness of unknown origin. The problem is amplified when dealing with non-human patients with whom we’re less able to extract an in-depth history that could reveal where they picked up the unknown contaminant. For three decades, researchers in America have been trying to pinpoint what was causing the frequent and rapid deaths of eagles in Georgia, South Carolina, and North Carolina (no murderous loons this time). Not only has the offending contaminant been found, but researchers have also identified a chemical (most likely leaked by human activity) that turns it into a deadly cocktail.

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A study published in the journal Science spent years investigating water samples from a human-made lake which eventually led them to a new kind of blue-green algae – not actually algae, but an aggregation of cyanobacteria which can be harmful or even fatal depending on its toxic compounds. These previously unknown cyanobacteria needed to have been introduced to the environment somehow, and after a considerable investigation, the team was able to identify that an invasive Hydrilla weed was acting as a substrate on which the blue-green algae could grow. The cyanobacteria have been named Aetokthonos hydrillicola, meaning “eagle killer that grows on Hydrilla”.

The implications of this cyanobacteria’s presence grew as it was exposed to bromide in the water, which the researchers believe to have come from an anthropogenic source. These two things combined created a neurotoxin that affects both the birds eating the invasive Hydrilla (the raft for the cyanobacteria) as well as the animals eating those birds, such as eagles.

The neurotoxin has a devastating effect on the brains of those who ingest it, boring out holes in the white matter so that they develop what’s sometimes called a “swiss cheese brain”. There are telltale signs in affected birds who will soon succumb to the infection, such as drooping wings in eagles, while for other animals such as turtles and salamanders it manifests as convulsions.

“We want people to recognize it before taking birds or fish from these lakes,” said Susan Wilde, an associate professor of aquatic science at the Warnell School of Forestry and Natural Resources who worked on the discovery, to Sci Tech Daily. “For fish, it’s tough. I would avoid eating fish with lesions or some sort of deformities; we do see affected fish with slow swimming speeds, but anglers won’t be able to see that. We want people to know the lakes where this disease has been documented and to use caution in consuming birds and fish from these lakes.”

Given the neurotoxin is known to build up in the food chain (a phenomenon called bioaccumulation), it’s expected that it has the potential to infect human hosts eating catch from the waterways colonized with this invasive weed and its cyanobacteria stowaways.

“Seasonal environmental conditions promoting toxin production of A. hydrillicola are watershed specific,” wrote the study authors. “Increased monitoring and public awareness should be implemented for A. hydrillicola and AETX to protect both wildlife and human health.”

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