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Description
Blue-green algae (Microcystis aeruginosa) is a type of phytoplankton that is found in ponds and other freshwater environments. They arise following long spells of hot dry weather and hence bloom in the summer but are also assosiated with high levels of phosphate and nitrate in the water. These algae can be extremely toxic and can poision livestock, birds and sometimes dogs.
Signalment
Diagnosis
Test water for presence of blue-green algae. This can be done by fixing fresh samples in a 1:10 dilution of formalin or frozen water samples can be evaluated for lethality using a mouse bioassay. Althouh non-specific, a biochemical profile suggests hepatotoxicity with increases in ALT, AST and ALKP.
History and Clinical Signs
History of drinking from stagnant water. Can be variable but in acute cases death can occur within a few hours. In less severe cases liver damage causing jaundice and photosensitisation may lead to death. generalised signs may include severe abdominal pain, vomiting and bloody diarrhoea, muscle tremors, convulsions, hyperaesthesia, staggering, dullness, recumbency, ataxia, flaccid paralysis.
Pathology
Petechiae in the heart. Congestion of the lungs, liver, mesenteric vessels and lymph nodes. Inflammatory and congestive changes in the gastrointestinal tract. Swollen liver, centrilobular necrosis and oedema of the gallbladder. Confirmatory tests:
Treatment
There is no specific anti-dote.
With a history of recent ingestion, gastric decontamination can be performed unless there is evidence of impaired neurological status. Detoxifixation and supportive treatment for the diarrhoea, dehydration, shock and hepatic insufficiency. Keep animals away from infected water. Add algicides such as copper sulphate to the water. Prognosis:
Prognosis
Poor. Dependent on the degree of liver damage and quantity ingested. Prompt treatment is essential.
Hepatotoxicity
Clinical
- prostration and death
- perhaps convulsions
- gastroenteritis in lesser cases
Gross
- haemorrhagic gastroenteritis
- massive or periacinar hepatic necrosis
Mechanism of toxicity
Blue green algae causes toxicity by metabolism into the cyclic peptide, microcystin. This causes dysfunctional phosphorylation of cellular keratins, leading to disruption of the normal cytoskeleton. This in turn leads to a "rounding up" effect of the hepatocytes, disruption of the hepatic sinusoids, separation of hepatocytes and excessive apoptosis, which all will result in liver failure.
Neurotoxins anatoxin-a and anatoxin-a(s) are prodcued by other blue-green algae. Anatoxin-a is a potent post-synaptic depolarizing neuromuscular blocker. Anatoxin-a(s) is a potent acetylcholinesterase inhibitor.