Microcystis aeruginosa

Abstract

DISTRIBUTION: Gauteng, Mpumalanga, N.E. Free State, Vaal dam, Hartebeespoort dam and Roodeplaat dam, now also Western and Eastern Cape Provinces. Botanical description: General: • These fresh water, blue-green algae that grow naturally in many surface waters, are phototrophic cyanobacteria which differ from other groups of algae in that they possess no nuclear membrane. • Under certain conditions (such as when the water is warm with abundant nutrients), Microcystis aeruginosa can grow more rapidly than normal. The result can be large colonies that form floating masses on the water. These occurrences are called "algal blooms". • On calm, hot, fine days the algae rise to the surface of the water and looks like green pea soup that is blown by the wind against the leeward banks of dams, etc. • Here the accumulated mass of algae may die to release a blue to purple chromoprotein, phycocyanin, and an offensive smell hangs in the air. • Since the cells are very small, they can be ingested along with the water.

TOXIC PRINCIPLE: • Hepatotoxic principle is not phycocyanin, but heptapeptides, e.g. microcystin LR, and phylloerythrin is the photodynamic agent. • The microcystin toxins are produced and contained inside the Microcystis cells,and are released in the water when the cells die and disintegrate. • Since the cells are very small, they can be ingested along with the water and disintegrate and are released in rumen/stomach. • Toxin levels in a water body tend to be higher near shorelines and at the surface of the water where animal and human contact is most likely.

SYNDROMES: Hepatogenous photosensitivity primarily due to liver parenchymal damage.

SYSTEMS AFFECTED: Liver.

CLINICAL SIGNS: • Ruminants are most commonly affected, and signs of photosensitivity are also seen. • Horses, dogs, turkeys, ducks can also be affected - severe liver damage, but no photosensitivity. Signs: • Acute deaths - Massive liver failure. - Pooling of blood in the liver. • Subacute toxicicity - Liver damage and secondary photosensitivity - Anorexia, - Rumen stasis, - Constipation

NECROPSY: Macroscopical findings: Acute: • Liver swollen, greyish-yellow (hepatic necrosis and haemorrhage) Subacute: • Kidneys swollen• Icterus, signs of photosensitivity• Caecum and colon impacted.

DIAGNOSIS: • History, clinical signs, necropsy findings • Mouse bioassay• HPLC analysis.