ISSN 2398-2969      

Blue-green algae poisoning


Larry Thompson

Nicola Bates

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


  • 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.
Print off the owner factsheet on Blue-green algae poisoning to give to your client.



  • 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.


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login


This article is available in full to registered subscribers

Sign up now to start a free trial to access all Vetlexicon articles, images, sounds and videos, or Login

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.


Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field