However, toxic blue green algae also will grow in stagnant small paddles of water and in water collection vessels on farm if left uncleaned for a long time. The microcystins will poison the liver rather acutely. In some cases, affected cattle die within a few hours of exposure. In subacute cases, death may come in a day or so. Microcystin LR, the predominant prototype microcystin, causes massive centrilobubar hepatic necrosis.
Shock is a result of hemorrhage within the liver caused by massive liver injury. In a natural setting of an algal bloom several microcystins (with different potencies) are produced. In some cases anatoxins are present at the same time.
Anatoxins are the second class of blue green algal toxins most responsible for livestock poisoning in Michigan. The anatoxins are structurally different from the microcystins and are also structurally different among themselves.
As mentioned earlier, these target the nervous system. They are produced by Anabaena, Planktothrix, Oscillaria, and Microcystin species. Some of these same species also produce microcystins. It is possible to have both microcystins and anatoxins produced in an algal bloom.
Two common anatoxins are produced (i.e., Anatoxin a and Anatoxin a(s). Anatoxin a is a nicotinic agonist at the cholinergic receptors. Intoxication results in a very rapid (minutes to a few hours) onset of rigidity and muscle tremors, paralysis and death by respiratory paralysis.
On the other hand, Anatoxin a(s) is an irreversible acetylcholinesterase inhibitor. In this regard, its toxic mechanism is similar to that of organophosphorous or carbamate insecticides with the exception that Anatoxin a(s) does not cross the blood-brain barrier while the insecticides do.
Clinical signs are all related to the effects of this toxin to the peripheral nervous system and include salivation, lacrimation, urination, diarrhea (SLUD), tremors, ataxia and convulsions. Affected animals die of respiratory paralysis. There are no gross or histological lesions in animals that have died of anatoxin intoxication.
Death comes quickly, usually in a matter of minutes to hours and may occur in the vicinity of the contaminated water body. There is no antidote for Anatoxin a intoxication. Treatment is supportive and includes respiratory support and anti-seizures medications. Atropine is an antidote for Anatoxin a(s) intoxication. 2-PAM is not effective and should not be given. The rest of the treatment is supportive and involves respiratory support and anti-seizure medications.
Diagnosis of microcystin intoxication involves water analysis for microcystins, microscopic water and gastrointestinal content examination for the cyanobacteria, and tissue analysis for bound microcystins. For morphological identification, a water sample in a glass jar in the ratio of 50:50 water: neutral buffered formalin solution can be analyzed at the diagnostic lab. There is no antidote to microcystins and there is no proven effective therapy. In this regard, prevention is the cure.
Diagnosis for Anatoxin a(s) intoxication includes whole blood cholinesterase assay, analytical confirmation of the toxin in water, stomach contents, and in the tissues. The brain cholinesterase test is not useful as these toxins do not cross the blood-brain barrier. Morphological identification of toxin-generating algae in water is also beneficial.