Diarrhoeic Shellfish Poisoning (DSP) in humans is caused by the ingestion of contaminated bivalves such as mussels, scallops, oysters or clams. The fat soluble DSP toxins accumulate in the fatty tissue of the bivalves. DSP symptoms are diarrhoea, nausea, vomiting and abdominal pain starting 30 minutes to a few hours after ingestion and complete recovery occurs within three days. DSP toxins can be divided into different groups depending on chemical structure. The first group, acidic toxins, includes okadaic acid (OA) and its derivatives named dynophysistoxins (DTXs). The second group, neutral toxins, consists of polyether-lactones of the pectenotoxin group (PTXs). The third group includes a sulphated polyether and its derivatives the yessotoxins (YTXs) (see Figures 3.1 and 3.2).
DSP toxins are produced usually by dinoflagellates that belong to the genera Dinophysis spp., however, the dinoflagellate genus Prorocentrum has also been found to be a producer of DSP toxins. DSP toxin production may vary considerably among dinoflagellate species and among regional and seasonal morphotypes in one species. The number of dinoflagellate cells per litre of water needed to contaminate shellfish is also variable. The most affected areas seem to be Europe and Japan. DSP incidences, or at least the presence of DSP toxins, appear to be increasing and DSP toxins producing algae and toxic bivalves are frequently reported from new areas.