Canis ISSN: 2398-2942

Blue-green algae poisoning

Synonym(s): Cyanobacteria, Anacystis cyanacea, Nodularia toxica, Anabaena, Aphanazomenom, Geotrichia, Microcystis, Oscillatoria

Contributor(s): Larry Thompson, Nicola Bates


  • Cause: ingestion of cyanobacterial species known to produce toxins under certain conditions.
  • Seasonal heavy growths between June and December.
  • Signs: toxicity → wide range clinical signs including neurotoxicosis, hepatotoxicosis, nephrotoxicosis or a combination if more than one cyanobacterial species involved.
  • Diagnosis: history, clinical signs, identification of algae.
  • Treatment: fluid therapy, emetics, activated charcoal.
  • Prognosis: poor - animals can recover → treatment worthwhile.



  • Exposure to toxins in water courses.
  • 'Algal blooms' occur on warm sunny days of late spring/summer .
  • High levels of nitrogenous compounds in water.
  • A high percentage of cyanobacteria produce toxins (hepatotoxins, cytotoxins, neurotoxins).
  • The relative concentration of each of the above varies with different species of cyanobacteria.
  • Blooms often have many constituent species and although there is usually a dominant type, there may be several toxins causing toxicosis.

Predisposing factors

  • Dogs which have a liking for water, eg gun dogs. Retrievers are particularly at risk.
  • Whilst some animals show aversion to algal blooms, dogs show a preference for cyanobacteria infested water even when given a clean water alternative.


  • Cyanobacteria often, but not always, have a blue-green color (can also be red, brown and black).  
  • It is believed that cyanobacterial toxicoses are associated with scums accumulating along leeward shores through wind and water movement → degeneration of the algae → release of intracellular toxins into the surrounding environment.
  • Dogs ingest this toxin while drinking, swimming or grooming → signs of alpha cyanobacterial species.
  • Toxic effects vary depending on:
    • Cyanobacterial species.
    • Stage of decomposition.
    • Ingested dose.
  • The principal documental syndromes are:
    • Acute hepatotoxicosis: caused by cyclic peptides → rounding and dissociation of hepatocytes → necrosis. Death results from hypovolemic shock Shock with hyperkalemia Hyperkalemia and/or hypoglycemia Hypoglycemia in protracted cases.
    • Nephrotoxicosis: tubular necrosis nephrosis has been reported in addition to hepatic changes.
    • Peracute neurotoxicoses: caused by depolarizing agent anatoxin-a (bicyclic secondary amine) → nicotinic receptors → respiratory paralysis → death. Death due to respiratory failure is also caused by anatoxin-a(s) (unstable cholinesterase inhibitor).
    • Gastrointestinal upset: often accompanies above syndromes and may be primary presenting sign. This might be due, in part, to the action of cyanobacterial liposaccharide endotoxins.
    • Some further toxins are cytotoxic.
    • Hepatotoxins suspected of → neoplasia (similar in action to okadeic acid).


  • Neurotoxicosis: sudden death or severe distress/convulsions within 15 minutes of ingestion.
  • Hepatotoxicosis: slower, less dramatic onset.
  • Course of disease: hours - several days.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Cherry C, Buttke D, Wong D, Wild, M A (2015) Freshwater harmful algal blooms and cyanotoxin poisoning in domestic dogs. JAVMA 247 (9), 1004-1005 PubMed.
  • Backer L C, Landsberg J H, Miller M, Keel K, Taylor T K (2013) Canine cyanotoxin poisonings in the United States (1920s-2012): review of suspected and confirmed cases from three data sources. Toxins 5 (9), 1597-628 PubMed.
  • Lürling M, Faassen E J (2013) Dog poisonings associated with a Microcystis aeruginosa bloom in the Netherlands. Toxins (3), 556-567 PubMed.
  • Sebbag L, Smee N, van der Merwe D, Schmid D (2013) Liver failure in a dog following suspected ingestion of blue-green algae (Microcystis spp.): A case report and review of the toxin. JAAHA 49 (5), 342-346 PubMed.
  • Faassen E J, Harkema L, Begeman L, Lurling M (2012) First report of (homo)anatoxin-a and dog neurotoxicosis after ingestion of benthic cyanobacteria in The Netherlands. Toxicon 60 (3), 378-384 PubMed.
  • Simola O, Wiberg M, Jokela J, Wahlsten M, Sivonen K, Syrjä P (2012) Pathologic findings and toxin identification in cyanobacterial (Nodularia spumigena) intoxication in a dog. Vet Pathol 49 (5), 755-759 PubMed.
  • Stewart I, Seawright A A, Shaw G R (2008) Cyanobacterial poisoning in livestock, wild mammals and birds - an overview. Advances in Experimental Medicine and Biology 619, 613-637 PubMed.
  • Gugger M, Lenoir S, Berger C, Ledreux A, Druart J C, Humbert J F, Guette C, Bernard C (2005) First report in a river in France of the benthic cyanobacterium Phormidium favosum producing anatoxin-a associated with dog neurotoxicosis. Toxicon 45 (7), 19-28 PubMed.
  • DeVries S E, Galey F D, Namikoshi M, Woo J C (1993) Clinical and pathological findings of blue-green algae (Microcystis aeruginosa) intoxication in a dog. J Vet Diagn Invest 5, 403-408 PubMed.
  • Gunn G, Rafferty A G, Rafferty G C, Cockburn N, Edwards C, Beattie K A, Codd G A (1992) Fatal canine neurotoxicosis attributed to blue-green algae.Vet Rec 130, 301-302 PubMed.
  • Corkhill N, Smith R, Seckington M & Pontrefract R (1989) Poisoning at Rutland Water. Vet Rec 125, 356 PubMed.
  • Mahmood N A, Carmichael W W & Pfahler D (1988) Anticholinesterase poisonings in a dog from a cyanobacterial bloom. Am J Vet Res 49, 500-503 PubMed.

Other sources of information

  • Chandler E A, Thompson D J, Sutton J B & Price C J (1991) Canine Medicine and Therapeutics, 3rd ed, Oxford: Blackwell Scientific Publications. pp 738.
  • National Rivers Authority (1990) Toxic blue-green algae. In: Water Quality Series No. 2.
  • Beasley V R, Cook W O, Dahlem A M, Hooser S B, Lovell R A & Velentine W M (1989) Algae intoxication in livestock and waterfowl. Veterinary Clinics of North America - Food Animal Practice 345-361 PubMed.