Cyanotoxins, related health hazards on animals and their management: A Review

Cyanobacteria are one of the largest subgroups of Gram-negative prokaryotic micro-organisms showing oxygenic photosynthesis. Under favorable environmental condition and nutrient enrichment of the water bodies these microorganisms may develop into toxic blooms. Nearly 25 to 75% of the cyanobacterial blooms produce secondary metabolites named cyanotoxins that may harm life forms like zooplankton, shellfish, fish, birds, and mammals. Cyanotoxins belong to a diverse group of chemical substances and can be grouped into: cyclic peptides, alkaloids or lipopolysaccharides; and may be neurotoxic, hepatotoxic, and dermatotoxic. The cyclic peptide toxins of the microcystin, nodularin and cylindrospermopsin family are the most frequent. Microcystis is the most predominant hepatotoxin producing cyanobacterium found in blooms and microcystin-LR is the most frequent microcystin variant and a major toxin in bloom. Anatoxins-a is a neurotoxic alkaloid and mimics acetylcholine activity. LD50 values of microcystins vary widely and range from 20 to 1,500 μg/kg body weight in fish whereas; the LD50 of Anatoxin-a is about 0.2 mg kg-1of body weight of mouse. However, correct identification of cyanotoxins is complicated due to production of more than one type of cyanotoxins in the same bloom. Moreover, these toxins exist in several variants and many of them are yet undescribed. Therefore, this article emphasizes the correct detection of cyanotoxins including their extraction, concentration/cleanup, preservation and determination methods besides, current knowledge about toxicological mechanisms of these cyanotoxins, treatments, and control of fatalities related to cyanotoxins by proper monitoring through prescribed guidelines and standards.