BACKGROUND: Paralytic shellfish poisoning (PSP) is a caused by ingestion of saxitoxin, a neurotoxin produced by dinoflagellate algae. These algae accumulate in bivalve mollusks (e.g., butter clams, razor clams, mussels, scallops, etc.) and crabs that consume them. Ingestion of shellfish contaminated with saxitoxin can result in a range of neuroparalytic symptoms, from mild numbness and tingling to complete paralysis and death due to respiratory failure. In Alaska, commercially-harvested shellfish and crabs are tested for saxitoxin prior to distribution; there is no systematic testing or monitoring of shellfish from recreational beaches.
METHODS: Between 1993 and 2015, the Alaska Section of Epidemiology (SOE) received reports of 119 PSP cases comprising 72 incidents. Response to these reports included identifying and monitoring cases, collecting contaminated food sources for lab testing, and working in partnership with the Alaska Department of Environmental Conservation (DEC) to provide public awareness and education.
RESULTS: Of the 119 PSP cases reported between 1993 and 2015, most required medical intervention and four were fatal. The most frequently reported shellfish sources for incidents of PSP were butter clams (n=26, 36%), mussels (n=12, 17%), cockles (n=12, 17%), or combinations of shellfish varieties (n=12, 17%). All of the contaminated food sources were personally harvested either for recreational sport or for subsistence use. While the majority of the incidents occurred in May or June, cases were reported throughout the year.
CONCLUSIONS: There is no risk-free time during the year to personally harvest shellfish in Alaska. Because recreationally-harvested shellfish are not routinely tested, and rapid field tests are not yet widely available or practical for subsistence harvesters, there is no reliable way for subsistence harvesters to determine if the shellfish they gather are safe to eat. Efforts to model the ecological factors that cause harmful algal blooms are ongoing.