• Cause: exposure to toxins produced by blue-green algae (cyanobacteria) can lead to an acute intoxication affecting either the liver or the central nervous system. 
• Signs: acute hepatotoxicosis with clinical signs of anorexia, depression, diarrhea, colic, weakness, pale mucous membranes and shock. Rapid onset of rigidity and muscle tremors, followed by paralysis, cyanosis and death. 
• Diagnosis: clinical signs, clinical pathology, postmortem findings, and analysis of water, supplements, or stomach contents. 
• Treatment: clean water, stall rest, and supportive care. 
• Prognosis: guarded to poor. 

• Blue-green algae blooms occur worldwide, and it has been recognized for over a century that they are responsible for deaths in livestock, birds, fish, wildlife and dogs. 
• Blue-green algae occur in both freshwater and marine environments and are either floating (planktonic) or bottom-dwelling (benthic). 
• In temperate regions blooms occur during late summer and early autumn and last 2-4 months but in subtropical environments the bloom can occur earlier and last longer. In dry years in tropical or subtropical areas blooms may occur throughout the year. 

• Toxins in water present exposure risk to other animals and humans. 
• Suspected blue-green algae exposure may be a reportable incident and animals often act as a sign of water body safety. 

• Multiple animals may be affected if drinking from the same water body. 

• Cyanobacteria (blue-green algae), such as Anabaena, Aphanizonemon, Microcystis, and Nodularia, are bacteria found in fresh, brackish and marine water bodies. They often have a blue-green color but can be red, brown or black .
• Under certain environmental conditions blue-green algae can quickly form extensive and often visible growths or blooms. These most commonly occur in warm weather (water temperature of 20°c or more) and affect the color, odor and taste of the water. 
• Not all blooms are toxic; it is not possible to identify species by eye. 
• Many cyanobacteria contain or produce a variety of toxic substances (cyanotoxins); many produce more than one type of toxin. 
• These toxins have high acute toxicity and exposures frequently result in fatality, which usually occurs very rapidly. 
• Ruminants appear to be more sensitive to this toxicity compared to monogastric species.  

General

• Access to contaminated water. 
• Bloom formation is dependent on a number of factors including species, strain and nutrient concentrations. Eutrophication from high fertilizer levels, sewage, animal waste and field run off is a common cause of algal blooms, and water bodies next to farmland are often affected. 
• Dietary supplements containing the blue-green algae Spirulina platensis and Aphanizomenon flos aquae (A. flos aquae) can be contaminated with microcystins. 

Specific

• Steady winds that concentrate toxic blooms to shore allow for ingestion by drinking animals. 
• Destruction of cyanobacteria proliferations (either naturally or through the application of herbicides or algicides) can result in a pulse of toxin release following destruction of the individual cells. 

• Many blue-green algae contain or produce a variety of toxic substances (cyanotoxins). 

Hepatotoxins

• Microcystins: potent inhibitors of protein phosphatases 1 and 2A leading to progressive centrilobular hepatocyte rounding, dissociation, and necrosis. 
• Cylindrospermopsin: a protein synthesis inhibitor; genotoxic through DNA fragmentation. 

Neurotoxins

• Anatoxin-a: potent cholinergic agonist at nicotinic acetylcholine receptors (nAChRs) in neurons and at neuromuscular junctions. 
• Anatoxin-as: irreversible acetylcholinesterase (AChE) inhibitor leading to cholinergic stimulation. 
• Saxitoxin and neosaxitoxin: fast acting sodium channel blockers. 

Other toxic compounds

• Many blue-green algae produce endotoxins that are irritant to skin and mucous membranes. 
• Some also produce dermatotoxic compounds such as lyngbyatoxin, aplysiatoxin and debromoaplysiatoxin. 

• Depends on the type of toxin involved and it is possible for more than one type of blue-green algae or toxin to be involved in the same incident, although there is usually a dominant type. 

Hepatotoxins

• Evidence of liver damage generally occurs within 24 h of ingestion, but death can occur within a few hours of days after exposure. 

Neurotoxins

• Signs of neurotoxin exposure can occur as early as 5-15 min after ingestion but may take up to one hour. 
• Death is also rapid, often within 10-30 min of the onset of clinical effects. 

Other toxic compounds

• Gastrointestinal signs can occur within 24 h. 
• Few cases of dermatotoxic effects are reported in animals but signs may occur within 24 h. 

• Water contamination during warm environmental temperatures can result in farm outbreaks. 

Refereed papers

• Recent references from PubMed and VetMedResource. 
• Nolen R S (2018) A One-Health solution to the toxic algae problem. JAVMA 252 (8), 906-908 AVMA.
• Mittelman N S, Engiles J B, Murphy L et al (2016) Presumptive iatrogenic microcystin‐associated liver failure and encephalopathy in a Holsteiner gelding. J Vet Int Med 30, 1747-1751 PubMed. 
• McGorum B C, Pirie R S et al (2015) Grazing livestock are exposed to terrestrial cyanobacteria. Vet Res 46, 16 PubMed. 
• Stewart I, Seawright A A & Shaw G R (2008) Cyanobacterial poisoning in livestock, wild mammals and birds – an overview. Adv Exp Med Biol 619, 613-637 PubMed. 
• Lopez-Rodas V, Maneiro E, Lanzarot M P, Perdigones N & Costas E (2008) Mass wildlife mortality due to cyanobacteria in the Donana National Park, Spain. Vet Rec 162 (10), 317-318 PubMed. 
• Hall J O (2006) Blue-green algae poisoning in large animals. 78th Western Veterinary Conference. 15-19 February, Las Vegas, Nevada. 
• Puschner B, Galey F D, Johnson B et al (1998) Blue-green algae toxicosis in cattle. JAVMA 213, 1605-1607 PubMed. 
• Frazier K, Colvin B, Styer E et al (1998) Microcystin toxicosis in cattle due to overgrowth of blue-green algae. Vet Human Toxicol 40 (1), 23-24 PubMed. 
• Beasley V R, Dahlem A M et al (1989) Diagnostic and clinically important aspects of cyanobacterial (blue green algae) toxicoses. J Vet Diagn Invest 1, 359-365 PubMed. 
• Dahlem A M, Hassan A S, Swanson S P, Carmichael W W & Beasley V R (1989) A model system for studying the bioavailability of intestinally administered microcystin-LR, a hepatotoxic peptide from the cyanobacterium Microcystis aeruginosa. Pharmacol Toxicol 64 (2), 177-181 PubMed. 
• Galey F D, Beasley V R, Carmichael W W et al (1987) Blue-green algae (Microcystis aeruginosa) hepatotoxicosis in dairy cows. Am J Vet Res 48 (9), 1415-1419 PubMed. 
• Kerr L A, McCoy C P & Eaves D (1987) Blue-green algae toxicosis in five dairy cows. JAVMA 191 (7), 829-830 PubMed. 
• Galey F D, Beasley V R, Carmichael W W, Kleppe G, Hooser S B & Haschek W M (1987) Blue-green algae (Microcystis aeruginosa) hepatotoxicosis in dairy cows. Am J Vet Res 48 (9), 1415-1420 PubMed. 

Other sources of information

• Puschner B (2018) Cyanobacterial (Blue-Green Algae) Toxins. In: Veterinary Toxicology – Basic and Clinical Principles. 3rd edn. Ed: Gupta R C. Elsevier, USA. pp 763-777. 

• ASPCA Animal Poison Control Center. Tel: +1 (888) 426-4435; Website: www.aspca.org.  
• Veterinary Poisons Information Service (VPIS). Tel: + 44(0) 2073 055 055; Website: www.vpisglobal.com.