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Fall 1996 Newsletter

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Blue-Green Algae Poisoning in Animals

Summary: The growth of highly toxic blue-green algae can occur in the waters of Indiana. Poisoning by the neurotoxins causes rapid death with or without signs of cholinesterase inhibition. Poisoning by the hepatotoxins causes massive liver necrosis with severe intrahepatic hemorrhage and death. Diagnosis is based on history of exposure, clinical signs, blue-green algae in the GI tract, and necropsy findings.

Introduction: Blue-green algae are not true algae, but are cyanobacteria which grow in fresh water in temperate areas world-wide, including Indiana. Under the appropriate weather and water conditions, usually in the late summer or fall after a drought, the blue-green algae can form a rapidly growing "bloom". These blooms can occur in farm ponds and larger bodies of water forming a thick, often foul-smelling scum of brown, to green, to blue-green algae. Winds can then blow the blue-green algae to the shore and concentrate it wlierethe animals have to drink it with the water. In many instances, the algae will not be poisonous. However, sometimes, for unknown reasons, the blue-green algae in these blooms form ncuroloxinsor hepatotoxins which can prove deadly to animals drinking the water.

Neurotoxins:    Two neurotoxins can be produced by blue-green algae: anatoxin-a oranatoxin-a(s). The neurotoxins produced are extremely poisonous and can kill within a few minutes. They are so toxic that the animals are sometimes found dead next to the contaminated water. Animals poisoned with anatoxin-a show a rapid onset of rigidity and muscle tremors followed by paralysis, cyanosis, and death. Poisoning with anatoxin-a(s) (s is for salivation) causes cholin­esterase inhibition similar to organophosphorous/ carbamate insecticides. Therefore, the clinical signs are excessive salivation, diarrhea, urination, and death. In lethal cases, the nicotinic signs of tremors, incoordination, and paralysis may also be present. Anatoxin-a(s) does not appear to cross the blood-brain barrier so brain cholinesterase is not inhibited. Poisoning with either anatoxin-a oranatoxin-a(s) does not result in gross or microscopic lesions. Therefore, diagnosis is based on a history of exposure to blue-green algae, clinical signs and the possible presence of blue-green algae in the GI tract (see below).

Hepatotoxins: Some species of blue-green algae produce  hepatotoxins:  microcystin or nodularin. While extremely toxic, these do not kill livestock as rapidly as the anatoxins. Following ingestion of water containing a toxic amount of these poisons, GI disturbances, characterized by vomiting (depends on species), abdominal pain, and diarrhea (often bloody) frequently occur. This is followed by weakness, lack of responsiveness and death. In the liver, destruction of hepatocytesoccurs soon after ingestion. Rapid necrosis of the liver cells often results in severe hemorrhage into the liver which can cause shock and death. If death due to shock does not occur, then death results from liver failure often within 24 hours. In animals which survive, secondary (hepatogenous)photo-sensitization has been reported. On post-mortem examination, the liver is often enlarged, swollen and dark red. In some cases, there is significant edema around the gall bladder. Histologically, there is massive liver necrosis with severe intrahepatic hemorrhage.

Diagnosis: Toxicoses due to the neurotoxins or hepatotoxins are diagnosed based on history of exposure to blue-green algae in the water, clinical signs, the presence of blue-green algae in the GI tract and in the cases of the hepatotoxins, gross and histologic liver lesions. In addition to tissue samples, a small amount of contents from the duodenum and upper ileum should be collected and fixed in 10% neutral buffered formalin (NBF) for identification of blue-green algae. In cases of suspected blue-green algae poisoning, the algae should be collected from the suspected source soon after the incident. Great care should be taken to insure safety of the collectors. A gallon of the blue-green algae cells should be collected for toxin identification. Additionally, a 5 ml sample of cells should be mixed with an equal volume of 10% NBF to fix them for identification.

- by Scott Wallace, Class of 1997

- edited by Toxicology:

- Jennifer Harms, BS, Toxicology Technician,

- Christina Wilson, BS, Assistant Chemist,

- RobertEverson,PhD, Analytical Chemist

- Stephen Hooser,DVM, PhD, Toxicologist


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