September 3, 2024

An update on the recent shellfish poisoning event and the safety protocols in place

By Ashleigh Epps, WSG aquaculture specialist

In late May 2024, the Pacific coasts of Oregon and Washington experienced a  paralytic shellfish poisoning harmful algal bloom event. Thirty-one people became sick in Oregon over Memorial Day weekend, which triggered increased paralytic shellfish poisoning testing and the closures of harvest areas by the Department of Health.

No illnesses occurred in Washington. The last time Willapa Bay and Grays Harbor closed due to an outbreak of paralytic shellfish poisoning was in 1997, making this an uncommon event. However, with increased ocean warming, harmful algal blooms events are occurring more frequently. Protocols are in place to ensure safe consumption of shellfish in Washington state.

What is paralytic shellfish poison?

Paralytic shellfish poison is a naturally occurring biotoxin created by species of phytoplankton   within the genus Alexandrium. In humans, other mammals and birds, this biotoxin affects the nervous system, paralyzing muscles. The poison can result in severe illness and even death. Symptoms may include numbness of the mouth and limbs beginning in the minutes or hours after eating contaminated shellfish. Severe paralytic shellfish poisoning progresses rapidly to paralysis and respiratory arrest, and may require mechanical ventilation.

Why does paralytic shellfish poison occur?

Shellfish are filter feeders, which means they pump water through their systems to filter and consume algae from the water column. Phytoplankton from the genus Alexandrium can be in the water column year round, and shellfish consume it. Shellfish generally are able to clear toxins from their systems at different rates depending on the species of shellfish. However, paralytic shellfish poison can occur when there is an abundance of Alexandrium present in the water, also known as a harmful algal bloom. During these harmful algal bloom events, toxins accumulate in shellfish faster than they are able to clear it, resulting in an accumulation of the toxin.

Harmful algal blooms occur when conditions are optimal for rapid algae reproduction. High inputs of nutrients, warmer ocean temperatures, and calmer waters can all contribute to greater abundance of algal blooms. Other types of shellfish poisons (for example, amnesic shellfish poison and diarrhetic shellfish poison) caused by other types of algae are also common in Washington. However, the monitoring and communications within the state mean that humans have rarely been sickened by consuming shellfish over the last 30 years.

Monitoring and protocols for safe shellfish consumption in Washington

The Washington Department of Health monitors shellfish safety by routine testing programs at more than 100 sites in shellfish harvest areas at least every other week. When high levels of biotoxins are detected, the Department of Health closes the harvest areas and monitors them closely until the biotoxin levels are within the consumption limits. There are usually signs posted on beaches that indicate when the beaches are closed for recreational shellfish harvesting. Many local health jurisdictions put out press releases as well. Ensure recreationally harvested shellfish are safe to eat using the Department of Health’s list of public beaches and status and the Shellfish Safety Map of beach closures, which are always the first to be updated when there is a closure.

The Olympic Region Harmful Algal Bloom (ORHAB) Program and the Sound Toxins Monitoring Program monitor algae at least weekly at sites along Washington’s Pacific coast and inland marine waters, providing early warnings when harmful algal bloom species are present in the water. The Washington Department of Fish and Wildlife and many Tribes collaborate with the Department of Health, ORHAB, and Sound Toxins to monitor and manage shellfish harvest areas.

Signs and symptoms of paralytic shellfish poison consumption

There is no way to detect paralytic shellfish poison by sight, taste, or smell in shellfish, and there is no way to remove it:  cooking, freezing, or removing part of the shellfish will not remove the poison. An early symptom of paralytic shellfish poison is tingling of the lips and tongue. This can develop within minutes or hours of consuming the affected shellfish. Symptoms can progress to loss of control in the arms and legs and, in severe cases, difficulty breathing. If you are experiencing any of these symptoms after consuming shellfish it is essential to seek medical attention immediately.

For more information, please read the Gathering Safe Shellfish document and visit the Department of Health Paralytic Shellfish Poisoning webpage. If you are interested in volunteering for our Sound Toxins Monitoring Program please visit the Sound Toxins webpage for more information.

 

###

Washington Sea Grant, based at the University of Washington, helps people and marine life thrive through research, technical expertise and education supporting the responsible use and conservation of coastal ecosystems. Washington Sea Grant is one of 34 Sea Grant programs supported by the National Oceanic and Atmospheric Administration in coastal and Great Lakes states that encourage the wise stewardship of our marine resources through research, education, outreach and technology transfer.

wsg.uw.edu

Join the conversation: instagram.com/waseagrant and Facebook.com/WaSeaGrant.