Bovine Blue-Green Algae Toxicosis
Blue-green algae, also known as cyanobacteria, is capable of causing sudden death when high concentrations are ingested. This toxicity is known to occur worldwide and affects not only livestock, but wildlife, marine life, and humans as well. Blue-green algae tends to grow on the surfaces of farm ponds during the summer season. The algae's potency is derived from the toxins which it can produce under favorable environmental conditions. Good environmental growing conditions include warm, stagnant water with abundant nutrients and a breeze which blows the algael organisms shoreward for easier livestock consumption.
There are several species of algae capable of producing harmful toxins. These include Anabaena, Aphanizonemon, Microcystis, and Nodularia. Some genera produce either hepatotoxins, neurotoxins, or both. The most common culprit is Microcystis aeruginosa. This organism produces microcystins, which are hepatopeptides that cause severe hepatotoxicosis. Normally this toxin is confined within the cell wall; however, with cell death (following an algael bloom) or cell damage (following contact with an acidic stomach environment) the toxin is released. Animal size and species help to determine an individual's toxic dose but, generally, monogastrics seem less sensitive than ruminants and birds. Also, the bloom density and toxin concentration determine if an animal shows signs following ingestions of a few ounces or a few gallons.
The pathologic lesions caused by microcystin toxins include hepatic enlargement and congestion. The cut surface is usually friable and hemorrhagic. Histologically, there is congestion, hemorrhage, diffuse centrilobular hepatocyte rounding, dissociation, and necrosis. This rapidly leads to massive liver insufficiency, shock and death. Less commonly, certain algael species (Anabaena and Aphanizomenon) produce neurotoxins. These are referred to as anatoxins and they behave as nicotonic agonists or cholinesterase inhibitors causing muscle paralysis and sudden death from respiratory arrest.
Clinical signs of cows affected by blue-green algae toxicosis may include muscle tremors, paddling, dyspnea, watery or bloody diarrhea, cyanosis, convulsions, becoming comatose, and death usually 4-24 hours following ingestion. Animals that survive, especially cattle and horses, may develop photosensitization. Liver enzymes will also be increased.
Diagnosis of blue-green algae toxicosis is based on history of exposure, clinical signs, gross and histopathologic lesions, and a laboratory analysis of water samples and rumen content. The species of algae can be identified after fixing a fresh water sample and a rumen content sample in 1:10 dilutions of formalin. At least 2 liters of fresh bloom material should be kept refrigerated and submitted for high-performance liquid chromatography to identify potential toxins.
If one suspects blue-green algae toxicosis, cattle should be removed from the suspected water supply. Activated charcoal can be administered to decrease toxin absorption and atropine may serve to block acetylcholine receptors if neurotoxins are suspected. Copper sulfate (0.2-0.4 ppm) may be added to the water to control cyanobacterial growth. It is imperative that livestock not be watered from the toxic source for a mininum of five days following treatment because toxin release will be abundant with the onset of algae cell death.
-by Susie Lutz, Class of 2004
-edited by Dr. Leon Thacker, ADDL
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