OUTDOORS TIPS: Watch for amnesiac shellfish poisoning

When humans ingest the compound -- generally by eating shellfish or crab that have taken in the alga -- the medical syndrome it causes is called Amnesiac Shellfish Poisoning (ASP). The first dig of the 2008-09 razor clam season is scheduled for Oct. 16. Here are some information diggers should be aware of regarding ASP.

1. What causes it

Surges in abundance of these diatoms are among those referred to as Harmful Algae Blooms (HABs). ASP triggering blooms like their PSP causing counterparts are often misnamed "red tide." When flourishing they seldom present a significant hue in the water, so color is not a reliable indicator of a bloom state or the alga abundance. Through photosynthesis, domoic acid is produced as a metabolyte or waste compound by these organisms. Research on trigger mechanisms in ongoing, but buoyant HABs are most often found in warmer, near-shore waters floating into intertidal areas where shellfish take them in. While pollution nutrients also are suspected, HABs will occur in relatively pristine sea environs.

2. Occurrence and effects

Marine waters of both the North Atlantic and North Pacific coasts will have recurrent algae blooms that pose the threat of ASP. All filter feeding mollusks and crab can take in these marine algae as they feed. In Washington coastal and inland waters, domoic acid producing alga are most often associated with razor clams and crab, though other shellfish will concentrate the toxin in their edible tissue or filters. While the shellfish are not affected, direct poisoning of some fish occurs when they eat the alga. Indirect poisoning of birds and mammals occurs when they eat the fish or contaminated shellfish containing significant amounts of the active alga or its toxin.

3. Health consequences

In humans, domoic acid causes brain damage that manifests itself in permanent short-term memory loss. Mild domoic acid exposures produce early symptoms such as vomiting, abdominal cramping and diarrhea. Moderate to large ingestions bring on neurologic disorders, including memory loss, weakness, seizures and heart arrythmias. Digestive tract problems occur within 24 hours, while the more severe symptoms start in 48 hours. The ASP biotoxin is very durable and cannot be destroyed by cooking or freezing temperatures. Also there is no known antidote. Treatment involves stabilizing patients and resolving symptoms until the toxin dissipates in their systems.

Prevention

Refraining from eating naturally contaminated shellfish during and immediately after blooms is the best course of prevention. Surge blooms can occur in any month of the year, not just popular summer shellfish gathering months. Most vulnerable to ASP and other marine toxin syndromes are casual eaters of personally gathered shellfish. Watch for alerts, check state, county or provincial health authority marine biotoxin Webpages for status throughout waters.

Washington State health authorities routinely test razor clams from the five coastal beach management zones before scheduled recreational digs are opened. A portion of the state razor clam license fee pays for this monitoring. Commercial shellfish businesses monitor and test their products during gathering and before marketing to ensure they are safe.

Online ASP and other biotoxins updates and alerts are available at these links:

Department of Health's biotoxin program

Updated shellfish safety map

Domoic acid information.

The current marine alerts also are available on the Biotoxin Hotline at 1-800-562-5632.

Source: National Oceanic and Atmospheric Administration Northwest Fisheries Science Center, Washington Department of Health Domoic Acid Biotoxin Web site.