Cyanobacteria toxin poisons

Acute poisoning of humans by freshwater cyanobacteria as occurs with paralytic shellfish poisoning, while reported, has never been confirmed. Humans are probably just as susceptible as pets, livestock, or wildlife but people naturally avoid contact with heavy waterblooms of cyanobacteria. In addition, there are no known vectors, like shellfish, to concentrate toxins from cyanobacteria into the human food chain. Susceptibility of humans to cyanobacteria toxins is supported mostly by indirect evidence. In many of these cases, however, if a more thorough epidemiological study had been possible these cases probably would have shown direct evidence for toxicity. 

Cyanobacterial toxins (both marine and freshwater) are functionally and chemically a diverse group of secondary chemicals. They show structure and function similarities to higher plant and algal toxins. Of particular importance to this publication is the production of toxins which appear to be identical with saxitoxin and neosaxitoxin. Since these are the primary toxins involved in cases of paralytic shellfish poisons, these aphantoxins could be a source of PSP standards and the study of their production by Aphanizomenon can provide information on the biosynthesis of PSP s. The cyanobacteria toxins have not received extensive attention since they have fewer vectors by which they come in contact with humans. As freshwater supplies become more eutrophicated and as cyanobacteria are increasingly used as a source of single cell protein toxic cyanobacteria will have increased importance (39). The study of these cyanobacterial toxins can contribute to a better understanding of seafood poisons. 

Microcystis, Nostoc, and Oscillatoria (Planktothrix). Cyanobacteria toxins (cyanotoxins) include cytotoxins and biotoxins (neurotoxins anatoxin-a, anatoxin-a(s) and saxitoxins, and the hepatotoxins microcystins MCs, and nodularins), with biotoxins being responsible for acute lethal, acute chronic, and subchronic poisonings of wild/domestic animals and humans. In most of the reported cases, afflicted animals consumed water from water bodies where there was an obvious presence of cyano-bacterial scum on the water surface. More recent measurements of cyanobacterial toxins using sensitive modem analytical methods have often revealed high frequencies of toxic blooms even when animal poisonings have not been reported. 

Bacteria and protozoa in water can produce toxins that can cause illness or even death. Toxins prodnced in rivers, lakes, and reservoirs by cyanobacteria including Anabaena, Microcystis, and Nodularia have cansed adverse health effects in Australia, Brazil, England, and elsewhere in the world. There are abont 40 species of cyanobacteria that produce toxins from six chemical gronps. Cylindrospermopsin toxin (below) prodnced by cyanobacteria has poisoned people who have con-snmed water contaminated by the toxin. Surface scums of cyanobacteria are likely to have especially high levels of cyanobacteria toxins. 

Two other suspected alkaloid producing cyanobacteria strains, Anabaena flos-aquae NRC-525-17 and Aphanizomenon flos-aquae NH-5, are now being studied. The toxin of flos-aquae NRC-525-17 (anatoxin-a(s)) is thought to have CNS stimulating properties (7) and that of Aph. flos-aquae NH-5 (aphantoxin) is thought to produce the paralytic shellfish poisons saxitoxin and neosaxitoxin (Fig. 1)... 

Cyanobacterial (Blue-Green Bacteria) Toxins. Cyanobacterial poisonings were first recognized in the late 1800s. Human poisonings are rare however, kills of livestock, other mammals, birds, fish, and aquatic invertebrates are common. It is caused by a variety of biotoxins and cytotoxins, including anatoxin, microcystin, and nodularin produced by several species of cyanobacteria, including Anabaena, Aphanizomenon, Nodularia, Oscillatoria, and Microcystis. The main contamination problems include all eutrophic freshwater rivers, lakes, and streams. 

Saxitoxin (32) is listed in Schedule 1 of the CWC. It is a polar, cationic, relatively low molecular mass toxin and is one of 18 structurally related neurotoxins collectively known as paralytic shellfish poisoning (PSP) toxins. Analogues are formed by addition of sulfate, A-sulfo and A-hydroxyl groups, and by decarbamylation. They block neuronal sodium channels, and thereby neurotransmission, death resulting from respiratory paralysis. Saxitoxin is produced by dinoflagellate species (and by some freshwater cyanobacteria), and accumulates in shellfish. The cationic nature of saxitoxin makes capillary electrophoresis combined with... 

Cyanobacterial toxins produced and released by cyanobacteria in freshwater around the world are well documented [158,159]. Microcystins are the most common of the cyanobacterial toxins found in water, as well as being the ones most often responsible for poisoning animals and humans who come into contact with toxic blooms and contaminated water [ 160]. Acute exposure results in hepatic injury, which can in extreme cases prove fatal. One such incident occurred that resulted in the death of over 50 dialysis patients due to the use of microcystin-contaminated water in the treatment [161]. Chronic exposure due to the presence of microcystin in drinking water is thought to be a contributing factor in primary fiver cancer (PLC) through the known tumour-promoting activities of these compounds [162],... 

Reports of AN-a(s) are much less common when compared with the extensive worldwide distribution of AN (Table 8.1). AN-a(s) has been identified in cyanobacteria from lakes in Demnark and in the stomach contents of poisoned birds (Henriksen et al. 1997). Among the factors that may have contributed to the low incidence of AN-a(s) reports are the instability of the toxin and difficulties in detection due to a lack of commercially available analytical standard. AN-a(s) readily loses the methyT phosphate moiety to produce a nontoxic product, and investigations of suspected AN(s) poisonings should also involve a search for the degradation product. 

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