The cyanotoxin anatoxin-a is primarily produced by freshwater cyanobacteria genera during summer algal blooms when the water is warm. The cholinergic agonist anatoxin-a acts at nicotinic acetylcholine receptors in neurons and neuromuscular junctions, and may cause seizures, muscle fasciculations, collapse, shock, cyanosis, respiratory failure, and death. This case report described the case of a 2.5-year-old castrated male golden retriever presented to a clinic in Reno, Nevada, in early summer for evaluation of acute onset paraparesis after swimming in a man-made pond. The dog had also ingested algal material from a bucket adjacent to the pond. The dog demonstrated anxiety, ptyalism, and tremors upon presentation, which progressed rapidly to generalized fasciculations and lateral recumbency. Treatment with crystalloid fluids and activated charcoal was instituted, and 2 hours after presentation the dog developed acute mental depression, tensor rigidity, absent menace responses, tachycardia, intermittent premature ventricular contractions, and regurgitation. The dog had minimal ventilatory capability and was placed on mechanical ventilation. The owners elected euthanasia due to the guarded prognosis. Gross necropsy and sample analysis were performed, and gastric contents, bucket contents, pond water, bile, and urine were positive for anatoxin-a using newly-developed testing. A Phormidium species anatoxin-a producer was identified in the bucket and stomach contents.
Commentary: Unless there has been clear-cut ingestion or exposure to material that can be identified as toxic to animals, veterinarians often must make an educated guess whether the patient may be suffering from intoxication. This case report eloquently describes severe neurologic signs in a dog following ingestion of anatoxin-a formed by cyanobacteria, as well as identification of the toxin in various bodily fluids. Unfortunately, in veterinary medicine, we too frequently lack the ability to identify whether a patient with suspected intoxication truly has ingested the material in question. The unique feature of this article is that the authors went a step beyond many others by developing a diagnostic assay to identify the toxin in future live patients.—Mark Troxel, DVM, Diplomate ACVIM (Neurology)
Treatment and diagnosis of a dog with fulminant neurological deterioration due to anatoxin-a intoxication. Puschner B, Pratt C, Tor ER. J VET EMERG CRIT CARE 20:518-522, 2010.