Diarrhetic Shellfish Poison (DSP)
In Europe, the consumption of shellfish that have filtered cells of the dinoflagellate genus Dinophysis have led to cases of intestinal upset. Two varieties appear responsible for DSP: Dinophysis acuta and D. acuminata. Because of these symptoms, this syndrome has been designated as Diarrhetic Shellfish Poisoning or DSP. DSP is a significant problem in northern Spain, Ireland, and the Mediterranean/Adriatic Sea. The toxin has been detected in shellfish in Eastern Canada. While no cases of DSP have ever been reported along the West coast of the U.S., the organisms that cause this poisoning are commonly found in British Columbia and Puget Sound in Washington State. Very recently (in 2003), the toxins have been detected in shellfish from British Columbia and are more than likely to be found wherever the organisms are present. The toxin in DSP appears to be okadaic acid and some related compounds, the dinophysistoxins. The toxins are fat soluble, have high molecular weights, and belong to a class of compounds called polycyclic ethers. Interestingly, these compounds (see chemical structures below) are somewhat similar in chemical structure to the rather exotic marine toxins that are associated with Ciguatera Fish Poisoning or Tropical Fish Poisoning in that the repeating polyether moieties are present in these molecules. While at first glance, diarrhea would appear to be a relatively minor ailment compared to symptoms of PSP and domoic acid; the DSP toxins have been reported to be tumor promoting agents. Due to the relatively minor and generic symptoms associated with DSP, it is difficult to diagnose whether outbreaks of this particular poisoning have occurred in the U.S.
{Structure after E.P. Carmody, K.J. James, S.S. Kelly, and K Thomas in Harmful Algal Blooms (P. Lassus, G Arzul, E. Erard, P. Gentien, C. Marcaillou Editors) 1995. page 273.} Risk Management of DSP Up until recently, DSP was managed by mouse bioassay and/or monitoring shellfish growing waters for the presence of Dinophysis organisms. Within the last decade or so, chromatographic tecniques using HPLC have been developed that permit both quantification and identification of the toxins. These techniques, while accurate, require well equipped laboratories with expensive equipment (i.e., HPLCs and perhaps mass spectrometers). Recently, molecular biological methods based on ELISA have been developed. For the future, these procedures, offer the potential for much lower costs, rapid assessment, and also field testing. Because they have very large shellfish industries, Ireland and Spain have implemented extensive monitoring programs for DSP. Nevertheless, if monitoring costs are to be controlled, we need a far better understanding of the life cycle of Dinophysis and toxin production. A full understanding of the production of the toxins by Dinophysis has proved difficult because the laboratory culturing of this dinoflagellate has proved very challenging. For reasons that are not understood, the organism can only be grown through one or two generations under laboratory conditions. Until the organism can be cultured in sufficient quantities, studies on the toxins will be hampered.
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