Occurance of Paralytic Shellfish Poison (Saxitoxin) in Shellfishes of Karnataka

Paralytic shellfish poisoning in man is caused by a potent toxin called saxitoxin, which is neuro-toxic and produced by marine toxic dinoflagellates. Various vehicles of paralytic shellfish poisoning are clams, mussels, oysters, scallops and molluscs which become toxic by feeding on toxic dinoflagellates. The shellfishes, which accumulate the poison, are themselves not affected by the lethal toxin.

Paralytic shellfish poisoning poses a serious problem by virtue of the strong toxicity of the poison (minimum lethal dose in mice is 10 micrograms/kg). Its occurrence is well known in countries like U.S.A., Canada, Japan and other European countries, but the outbreak at Kumble near Kasargod in 1983 happened to be the first case reported in India. During this outbreak, paralytic shellfish poisoning had resulted in death of a boy and hospitalisation of several others following consumption of toxic clams and oysters.

Mouse bioassay techniques of Sommer & Meyer adopted by AOAC (Association of Official Analytical Chemists) has been method of choice for assay of poison levels. The permissible limit in edible shellfishes is 400 MU/100g. When the toxin levels exceed this limit, harvesting of shellfishes or sale should be prohibited from public health point of view. Incidentally, the toxin level detected in shellfishes at Kumble during the 1983 outbreak were of the order of 20,000 MU/100g which is a lethal dose for human beings. It was felt that if such a toxin occurs in shellfishes in other extuaries in Karnataka, it would pose a serious public health problem.