|Neoplasia and biotoxins in bivalves: is there a connection?|
Landsberg, J.H. (1996). Neoplasia and biotoxins in bivalves: is there a connection? J. Shellfish Res. 15(2): 203-230
In: Journal of Shellfish Research. National Shellfisheries Association: Duxbury. ISSN 0730-8000, more
Biotoxins; Cancer; Epizootiology; Alexandrium Halim, 1960 [WoRMS]; Bivalvia [WoRMS]; Dinoflagellata [WoRMS]; Marine
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In the past 25 years, there has been an increase in the frequency of two major types of cancer in bivalves: disseminated neoplasia and germinomas, which cause debilitation and mortality in shellfish stocks. Disseminated neoplasia is common in softshell clams, Mya arenaria; the cockle, Cerastoderma edule; and blue mussels, Mytilus trossulus; and less common in edible oysters, Ostrea edulis; macomas, Macoma balthica; blue mussels, Mytilus edulis; and Olympia oysters, Ostrea conchaphila. Germinomas occur more frequently in northern quahogs, Mercenaria mercenaria, and softshell clams, Mya arenaria. Certain geographical locations, especially along the northwest Pacific and northeast Atlantic Coasts of North America and the Atlantic Coast of Europe, are "hot spots" for neoplasia. A genetic susceptibility of bivalves to tumor formation has been suggested, and the etiologies proposed include chemical carcinogens, viruses, and other transmissible agents. However, no clear cause-and-effect relationship has yet been conclusively demonstrated, nor has the potential role of biotoxins as etiological agents been examined. In the past 25 years, there has also been an increase in the frequency with which humans have been poisoned by consuming toxic bivalves. Filter-feeding bivalves accumulate biotoxins produced by toxic microalgal blooms. This study traces the worldwide distribution of paralytic shellfish poisoning (PSP), diarrheic shellfish poisoning, neurotoxic shellfish poisoning, amnesic shellfish poisoning, and venerupin shellfish poisoning and of the microalgae and bivalve species associated with the poisonings and then compares these distributions with the distribution of neoplasia in bivalves. The incidence of disseminated neoplasia in some affected bivalve species appears to parallel, both spatially and temporally, outbreaks of PSP that are associated with the toxigenic dinoflagellates Alexandrium tamarense, A. minutum, A. fundyense, and A. catenella. Shellfish that have accumulated potent saxitoxin and its derivatives (neosaxitoxin and gonyautoxins) produced by these dinoflagellates are highly toxic to humans. The presence of disseminated neoplasia parallels the presence of certain toxin derivatives in both the bivalve and the Alexandrium spp. to which the bivalves are exposed. Disseminated neoplasia is common in softshell clams, M. arenaria, that have apparently been exposed to and have accumulated gonyautoxins, (GTX), and in particular GTX1 and GTX4, that are produced by A. tamarense or A. fundyense. M. mercenaria is apparently not affected by disseminated neoplasia and does not usually accumulate toxins associated with A. tamarense or A. fundyense. Bivalves that accumulate high concentrations of saxitoxin or neosaxitoxin, such as butter clams, Saxidomus giganteus; surf clams, Spisula solidissima; sea scallops, Placopecten magellanicus; and California mussels, Mytilus californianus, are apparently not affected by disseminated neoplasia or germinomas. In M. arenaria, the incidence of germinomas appears to be related to the distribution of Alexandrium spp. blooms. In M. mercenaria, however, the distribution of germinomas is not related to those Alexandrium spp. that are commonly associated with PSP. The incidence of disseminated neoplasia and germinomas is not correlated with PSP outbreaks associated with Pyrodinium bahamense var. compressum or Gymnodinium catenatum. Although the epizootiological evidence presented here for a correlation between dinoflagellate toxin profiles, the deposition of toxins in bivalve tissues, and the presence of neoplasia in such bivalves is circumstantial, it should be investigated in field and laboratory experiments.