SACRAMENTO - The statewide annual quarantine on mussels taken by sport harvesters from the ocean waters of California for human consumption will end at midnight on Tuesday, Oct. 31, except in San Luis Obispo County, State Public Health Officer Dr. Mark Horton announced today. Extensive sampling of mussels confirmed that shellfish-borne paralytic shellfish poisoning (PSP) toxins are at safe or undetectable levels, except in San Luis Obispo County.

The quarantine is issued for the entire California coastline, usually from May 1 through Oct. 31, to protect consumers of sport-harvested shellfish from PSP and domoic acid poisoning. The quarantine applies only to sport-harvested mussels. Commercial shellfish harvesters in California must be certified by the California Department of Health Services (CDHS) and are subjected to stringent sample testing for toxins. Commercial harvesting is stopped immediately if a potentially dangerous level of toxin is found.

PSP is a form of nervous system poisoning. Concentrated levels of the PSP toxins can develop in California mussels and other bivalve shellfish when they feed on certain naturally occurring marine plankton. Shellfish become toxic only when populations of the responsible organism, a dinoflagellate known as Alexandrium catenella, become abundant in ocean waters -- a phenomenon known as a "bloom." Bivalve shellfish feed by filtering the microscopic organisms from the water and concentrate the toxin in their bodies.

Domoic acid was first recognized as a cause of poisoning in Canada in 1987 when 107 people became ill and three died after eating toxic mussels harvested on the Atlantic coast. This toxin was observed for the first time on the Pacific Coast in September 1991 when it was found to be the cause of death of hundreds of pelicans and cormorants in the vicinity of Santa Cruz.

It has subsequently been linked to several episodes of severe poisoning of marine mammals along the coast. Several mild cases of human poisoning from domoic acid may have occurred in the state of Washington in 1991 in consumers of toxic razor clams from beaches north of the Columbia River.

The source of domoic acid in seafood is several species of marine diatoms in the genus Pseudo-nitzschia. Besides bivalve shellfish, the viscera of anchovies, sardines, spiny lobsters and several species of crabs has been found at times to contain unsafe amounts of domoic acid. Toxic anchovies were the source of domoic acid in the Santa Cruz incident.

Consumers can receive updated information about PSP and domoic acid by calling CDHS' "Shellfish Information Line" at 1-800-553-4133.

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