Dr. Mark Horton, director of the California Department of Public Health (CDPH), announced today that the statewide annual quarantine on mussels taken by sport harvesters from the ocean waters of California for human consumption ended today. Sampling of mussels confirmed that shellfish-borne paralytic shellfish poisoning (PSP) toxins and domoic acid poisoning are at safe or undetectable levels.
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 CDPH and are subject 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.
Another toxin of concern associated with shellfish is domoic acid. It was first recognized as a cause of poisoning in humans in an outbreak in Canada in 1987 when approximately 150 people became ill and four died after consuming toxic mussels from Prince Edward Island on the Atlantic Coast. The source of the domoic acid in this outbreak was a diatom known as Pseudo-nitzschia pungens forma multiseries. This single-celled marine algae, like dinoflagellates, is a natural food source for filter-feeding animals.
The first documented occurrence of domoic acid on the Pacific Coast of the United States was in September and October 1991 in the vicinity of Santa Cruz on Monterey Bay. Domoic acid was found to be the cause of death of several hundred brown pelicans and Brandt’s cormorants. The birds were exposed to domoic acid by feeding on anchovies, which feed on plankton.
Domoic acid 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.
Consumers can receive updated information about PSP and domoic acid by calling the CDPH "Shellfish Information Line" at 1-800-553-4133.