Paralytic shellfish poisoning; A review

Abstract

Paralytic shellfish poisoning (PSP) is caused by ingestion of shellfish containing PSP toxins. The PSP toxins are a group of 18 closely related tetrahydropurines. The first PSP toxin chemically characterised was saxitoxin. The various PSP toxins significantly differ in toxicity, with saxitoxin being the most toxic. The presence of PSP toxins in shellfish can be demonstrated with the mouse bioassay, a non-selective testing procedure, with animal death as toxicity criterion. The test is currently used in many countries for checking the toxicity of shellfish but international pressure a.o. of animal welfare groups has led to stimulation of research to replace the mouse bioassay by chemical methods of analysis. It is expected, however, that several more years of intensive investigations will be needed, before a selective, sensitive and validated method of analysis becomes available and accepted. Although promising developments have been made, limited supplies of purified toxin standards are still delaying rapid progress. The PSP toxins are produced mainly by dinoflagellates belonging to the genus Alexandrium, which may occur both in the tropical and moderate climate zones. Shellfish grazing on these algae can accumulate the toxins , but most of them are rather resistent to the harmful effects of these toxins. The highest concentrations in shellfish are found during or directly after an algal bloom. People consuming the contaminated shellfish can become intoxicated. The primary mode of action of PSP toxins in mammals is their binding to sodium channels in nerve cell membranes, readily at nanomolar concentration. This leads to inhibition of impulses along the nerves, resulting in paralysis, respiratory depression and circulatory failure. Symptoms of human PSP intoxication vary from a slight tingling or numbness to complete respiratory paralysis. In fatal cases, respiratory paralysis occurs within 2-12 hours of consumption of the PSP containing food. During the last 20 years there seems to be an increase in intoxications, caused by PSP. Currently, some 25 countries have regulations for PSP. Most regulations are set for paralytic shellfish poisoning as a group, but some countries indicate specific regulations for one of the PSP toxins, mostly saxitoxin.