Pulling Mussels from a Shell’ Leads to Diarrhetic Shellfish Poisoning
ABSTRACT & COMMENTARY
"Of all the creatures living in the water, you may eat any that has fins and scales. But anything that does not have fins and scales you may not eat; for you it is unclean."
By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University, Hospital Epidemiologist, Sequoia Hospital, Redwood City, CA, Editor of Infectious Disease Alert.
SYNOPSIS: Home-caught and cooked mussles in Canada and those served at restaurants in Washington state had elevated toxin levels that resulted in diarrhetic shellfish poisoning.
SOURCES: Lloyd JK, et al. Diarrhetic shellfish poisoning, Washington, USA, 2011. Emerg Infect Dis 2013;19:1314-6.
Taylor M, et al. Outbreak of diarrhetic shellfish poisoning associated with mussels, British Columbia, Canada. Mar Drugs 2013; 11;1669-76. (Abstract): http://ow.ly/nV7od
Public health authorities in Seattle and King County were notified in July 2011 of a cluster of cases of diarrheal illness occurring in 3 of 4 members of a family that had eaten mussels that they themselves had harvested and cooked. The 3 affected members, ages 2, 5, and 45 years, had eaten 8-15 mussels while the fourth, unaffected member, had only eaten 4. Symptoms began 4, 7, and 14 hours after their meal and included vomiting, diarrhea, body aches, fever and chills. The illness was self-limited with all 3 being well by 96 hours. Vomiting lasted for a mean duration of 3 hours while the mean duration of diarrhea was 52 hours.
Mussel samples collected from implicated public dock site were found to have excess toxin levels. Clams and oysters harvested from an adjacent commercial growing area were recalled (mussels were not commercially harvested). The park containing the public dock and the commercial site were closed until shellfish were cleared for harvesting based on reduced toxin levels.
Shortly after the Washington state outbreak, public health authorities in British Columbia were notified of the occurrence of gastrointestinal illness in individuals who had consumed cooked mussels at a number of restaurants. Investigation uncovered a total of 62 cases associated with 15 "food premises" where mussels had been eaten between July 28 and August 6. Symptoms, occurring after an incubation period of 5-15 hours and lasting 1-3 days most frequently included nausea, vomiting, diarrhea, and abdominal cramping pain.
The implicated mussels had been harvested at a single area in the Strait of Georgia between July 24-31 by a single enterprise that had taken steps to withdraw its product on August 3. Tested mussel samples contained elevated toxin levels.
COMMENTARY
Diarrhetic shellfish poisoning is one of a number of toxic events that may result from ingeston of these filter feeding marine molluscs. Diarrhetic shellfish poisoning is caused by the ingestion of excess amounts of okadaic acid group toxins as well as some related toxins.1 Okadoic acid potently inhibits mammalian protein phosphorylase phosphatases that dephosphorylate serine and threonine and is believed to cause diarrhea by stimulating the phosphorylation involved in controlling sodium excretion by intestinal epithelial cells. Okadoic acid and other toxins are produced by dinoflagellate algae, particularly Dinophysis. As filter feeders, shellfish act as concentrators of these lipophilic and heat stable toxins, an event exacerbated by increased density of these dinoflagellates, as occurs with algal blooms. There has, unfortunately, been a global increase in the frequency of algal blooms with consequent okadoic acid production and increasing contamination of shellfish. The reasons for the increased frequency of algal blooms are likely to be multifactorial but likely include climate change.
Diarrhetic shellfish poisioning was first identified in the Netherlands 5 decades ago. Most outbreaks are reported from outside North America, although these have occurred in eastern Canada. Although toxin-containing dinoflagellates have long been known to exist in Pacific Coast waters, these are the first reported cases of diarrhetic shellfish poisoning acquired in this region.
The incubation period is brief. In general, symptoms (nausea, vomiting, diarrhea, chills, abdominal pain) begin 30 minutes to 12 hours after ingestion and last for as long as 3 days. A similar syndrome that has been called azaspiracid shellfish poiosoning is caused by a group of toxins that differ from those causing diarrhetic shellfish poisoning.2 Treatment is supportive.
Reference
- Trainer VL, et al. Diarrhetic shellfish toxins and other lipophilic toxins of human health concern in Washington state. Mar Drugs 2013; 11:1815-35.
- James KI, et al. Shellfish toxicity: Human health implications of marine algal toxins. Epidemiol Infect 2010; 138:927-40.
