Dave

Hot weather means Blue Green Algae blooms may occur in shallow bodies of water.

Weather Conditions

Cyanobacteria blooms are more likely to occur when water temperatures rise to 85°F, adequate nitrogen and phosphorus are present in the water, and a light breeze blows algae to one side of the body of water. Water tanks or natural bodies of water take on a deep dark green to black color. The algae bloom is "in" rather than "on" the water. Water is brackish not translucent. Green material floating on the water is often duckweed.

Organisms

Cyanobacteria are commonly called Blue Green Algae. Many Cyanobacteria are not toxigenic. Common toxigenic Cyanophyta are Anabaena, Aphanizomenon, or Oscillatoria. Strains in each of these species may produce anatoxin-a, anatoxin-a(s), or both under the proper environmental conditions. Microcystis produce microcystin and Nodularia produce nodularin under the proper environmental conditions.

Exposure

Animal exposure to cyanophyta toxins normally occurs in July or August in Minnesota. The CVM (FDA Center for Veterinary Medicine) did see cases of Blue Green Algae toxicosis last October when temperatures were unseasonably warm. Livestock are commonly exposed in stock tanks, shallow ponds, or slews. Dogs, or rarely cats, are exposed when they drink from, or swim in, slews, or brackish shallow bays of lakes. The CVM has seen a case of markedly elevated liver enzymes in a cat given blue green algae tablets purchased from a health food store. The tablets were confirmed by gas chromatography-mass spectrophotometry (GC-MS) to contain microcystin.

Toxins and Clinical Signs

Anatoxin-a is most commonly produced by Anabaena flos-aquae. It depolarizes nicotinic membranes, so muscle fasciculations [twitches], tetany [tonic muscle spasms], lethargy, respiratory distress and convulsions may be observed. Anatoxin-a(s) inhibits cholinesterase activity, so salivation, urination, lacrimation [secretion of tears], defecation, tremors, dyspnea [labored respiration], convulsions and death may occur. Clinical signs are frequently observed within minutes to an hour of exposure.

Microcystin and nodularin are hepatotoxins. Microcystin inhibits phosphatases 1 and 2A, and alters microtubules and microfilaments, thereby altering the cytoskeleton. Apoptosis [cell self-destruction], blebbing [blistering], and DNA fragmentation can occur. Clinical signs including lethargy, vomiting, diarrhea, atony [lack of physiological tone], and death develop hours to days after exposure. Secondary photosensitization may be observed up to 10 days after exposure.

Diagnosis

The presence of cyanophyta may be confirmed by microscopic examination of water samples collected at the time of the bloom. Tom Arendt of the Toxicology unit in the College of Veterinary Medicine has 30 years of experience identifying these samples. The presence of the bloom does not confirm the presence of the toxins. GC-MS analyses of cyanophyta containing water can be run to confirm the presence of the toxins.

Animals exposed to anatoxin-a(s) may have a low blood, but not brain, cholinesterase. However, these animals often die before a blood sample can be collected. Animals exposed to microcystin or nodularin are likely to have markedly elevated liver specific enzymes or bile acids, an enlarged liver, and hepatic necrosis and hemorrhage histologically.

Treatment

There are no specific antidotes for the cyanobacteria toxins. General and supportive therapy includes decontamination with emesis [vomiting], activated charcoal, and a cathartic [purification or purgation]. Wear rubber gloves when bathing dogs that swim in cyanophyta infested water to avoid human exposure. Indicated supportive therapy may include aggressive fluids, glucocorticoids and other shock treatment, diazepam if seizures are present, and atropine if excessive salivation is present. Mannitol may be useful in hepatic necrosis cases.

Prognosis

The prognosis is grave in animals exposed to toxigenic cyanophyta. Animals may demonstrate hepatotoxic clinical signs or laboratory findings as long as 7 to 10 days after exposure.

Prevention

Copper sulfate is often used in stock tanks to limit algae growth in warm weather.

Miscellaneous

Check with a local realtor to determine if a diagnosis of blue green algae toxicosis on private land in your area may require a disclosure statement on the future sale of the real estate.

Source: Minnesota Veterinary Medical Association Watch - July 18, 2006