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Source: https://www.asbmb.org/asbmb-today/sc...t-s-killing-am
There’s something in the water, and it’s killing America’s national bird
By Irene Zhang
Sept. 4, 2021
In the winter of 1994, at DeGray Lake in Arkansas, 29 bald eagles died of unknown causes. Two years later, another 26 dead or dying eagles were found in the same area. Blood counts, chemical tests, and postmortem tissue examinations of the birds appeared normal, with no significant levels of toxic chemicals and no indication of bacterial or viral infections. Apart from being dead, the eagles appeared in good health.
What caused so many eagles to die so suddenly? Light microscopy finally provided a clue – all examined eagles showed widespread lesions in the white matter, or myelin, of their brains and spinal cords. These lesions took on the appearance of empty cavities, leading the researchers to name this disease Avian Vacuolar Myelinopathy (AVM). The cause of AVM remained unknown.
For over twenty years, AVM spread across the southeastern United States, affecting birds from American coots to red-tailed hawks. None of the affected birds showed signs of compounds or pathogens known to cause myelinopathy. But, the cases all had a few things in common. The mysterious deaths occurred during the fall or winter, near bodies of water colonized by the non-native aquatic plant waterthyme, Hydrilla verticillata. Further study showed that the surfaces of H. verticillata leaves were covered by a previously undiscovered cyanobacterium, Aetokthonos hydrillicola...
...The mass mortalities had been caused by a deadly combination of a non-native aquatic plant, H. verticillata, upon which the cyanobacterium A. hydrillicola lives. When bromine concentrations are low, this arrangement is relatively benign, but the duo turns deadly when bromine increases, possibly due to pollution from pesticides, power plants, or gasoline. H. verticillata accumulates bromine on its surfaces, and A. hydrillicola, in the presence of bromine, produces the toxin AETX. Birds and other animals feeding on this plant accumulate AETX in their bodies, and affected waterfowl may then be eaten by eagles and other birds of prey. After ingesting a lethal amount of AETX, these birds develop holes in their brain matter, and eventually die.
Native to India, H. verticillata was first sold as an aquarium plant, although it is now classified as a federally prohibited invasive and its sale is banned in the United States. However, it is already widespread in 33 states in the U.S. and across all continents except Antarctica. Currently, several methods of controlling its spread involve the use of bromine-containing herbicides, but this may pose a danger as bromine increases the production of AETX.
AETX is far from the first cyanobacterial toxin to be discovered. In fact, known cyanotoxins pose many health hazards if humans or pets ingest, inhale, or otherwise come into contact with them, and can cause gastrointestinal, liver, skin, and neural symptoms. Many affected water bodies, including DeGray Lake, are used by people for fishing, swimming, boating, and as sources of drinking water. AETX accumulates in lipids, may remain in the body for a period of time, transfers up the food chain, and has demonstrated lethality in a wide variety of animals. How does AETX affect humans? We don’t yet know. More research is required to fully understand the effects of AETX upon entire ecosystems and its longer-term effects to both wildlife and human health...
There’s something in the water, and it’s killing America’s national bird
By Irene Zhang
Sept. 4, 2021
In the winter of 1994, at DeGray Lake in Arkansas, 29 bald eagles died of unknown causes. Two years later, another 26 dead or dying eagles were found in the same area. Blood counts, chemical tests, and postmortem tissue examinations of the birds appeared normal, with no significant levels of toxic chemicals and no indication of bacterial or viral infections. Apart from being dead, the eagles appeared in good health.
What caused so many eagles to die so suddenly? Light microscopy finally provided a clue – all examined eagles showed widespread lesions in the white matter, or myelin, of their brains and spinal cords. These lesions took on the appearance of empty cavities, leading the researchers to name this disease Avian Vacuolar Myelinopathy (AVM). The cause of AVM remained unknown.
For over twenty years, AVM spread across the southeastern United States, affecting birds from American coots to red-tailed hawks. None of the affected birds showed signs of compounds or pathogens known to cause myelinopathy. But, the cases all had a few things in common. The mysterious deaths occurred during the fall or winter, near bodies of water colonized by the non-native aquatic plant waterthyme, Hydrilla verticillata. Further study showed that the surfaces of H. verticillata leaves were covered by a previously undiscovered cyanobacterium, Aetokthonos hydrillicola...
...The mass mortalities had been caused by a deadly combination of a non-native aquatic plant, H. verticillata, upon which the cyanobacterium A. hydrillicola lives. When bromine concentrations are low, this arrangement is relatively benign, but the duo turns deadly when bromine increases, possibly due to pollution from pesticides, power plants, or gasoline. H. verticillata accumulates bromine on its surfaces, and A. hydrillicola, in the presence of bromine, produces the toxin AETX. Birds and other animals feeding on this plant accumulate AETX in their bodies, and affected waterfowl may then be eaten by eagles and other birds of prey. After ingesting a lethal amount of AETX, these birds develop holes in their brain matter, and eventually die.
Native to India, H. verticillata was first sold as an aquarium plant, although it is now classified as a federally prohibited invasive and its sale is banned in the United States. However, it is already widespread in 33 states in the U.S. and across all continents except Antarctica. Currently, several methods of controlling its spread involve the use of bromine-containing herbicides, but this may pose a danger as bromine increases the production of AETX.
AETX is far from the first cyanobacterial toxin to be discovered. In fact, known cyanotoxins pose many health hazards if humans or pets ingest, inhale, or otherwise come into contact with them, and can cause gastrointestinal, liver, skin, and neural symptoms. Many affected water bodies, including DeGray Lake, are used by people for fishing, swimming, boating, and as sources of drinking water. AETX accumulates in lipids, may remain in the body for a period of time, transfers up the food chain, and has demonstrated lethality in a wide variety of animals. How does AETX affect humans? We don’t yet know. More research is required to fully understand the effects of AETX upon entire ecosystems and its longer-term effects to both wildlife and human health...