Algal Toxicosis
Basic Information 
Clinical Presentation
History, Chief Complaint
• Microcystins: diarrhea and weakness within hours of exposure to water
• Anatoxin-a: rapid onset of muscle rigidity, muscle tremors, and convulsions within minutes to a few hours of exposure to water
• Anatoxin-a(s): rapid onset of excessive salivation, diarrhea, tremors, and convulsions within minutes of exposure to water
Physical Exam Findings
• Microcystins: microcystin intoxication should be suspected in cases of acute hepatotoxicosis with clinical signs of diarrhea, nasogastric reflux, weakness, pale mucous membranes, and shock. Although most animals die within a few hours of exposure, some animals may live for several hours and develop hyperkalemia, hypoglycemia, nervousness, recumbency, and convulsions. Animals that survive the acute intoxication may develop hepatogenous photosensitization.
• Anatoxin-a: clinical signs of anatoxin-a poisoning include a rapid onset of rigidity and muscle tremors followed by paralysis, cyanosis, and death. Death usually occurs within minutes to a few hours. In most cases, the animal is found dead.
• Anatoxin-a(s): animals poisoned with anatoxin-a(s) show a rapid onset of excessive salivation (“s” stands for salivation), lacrimation, diarrhea, and urination. Nicotinic overstimulation results in tremors, incoordination, convulsions, recumbency, and respiratory arrest. Animals often die within 30 minutes of exposure and thus are often found dead.
Etiology and Pathophysiology
• Microcystins are cyclic heptapeptides that inhibit protein phosphatases, which leads to hepatocyte necrosis. There are more than 80 different microcystins worldwide produced by various genera of cyanobacteria, such as Microcystis, Anabaena, Planktothrix, Nostoc, Oscillatoria, and Anabaenopsis.
• Anatoxin-a is a potent cholinergic agonist at nicotinic acetylcholine receptors in neurons and at the neuromuscular junctions. Anatoxin-a is produced worldwide by cyanobacteria genera such as Anabaena, Plantkothrix, Oscillatoria, Microcystis, Aphanizomenon, Cylindorspermum, and Phormidium.
• Anatoxin-a(s) is a naturally occurring irreversible acetylcholinesterase inhibitor produced by cyanobacteria species such as Anabena flosaquae, Anabena lemmermannii, and Anabena spiroides.
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