Response to an Emerging Threat to Human Health: Diarrhetic Shellfish Poisoning in Washington State

The toxins associated with diarrhetic shellfish poisoning (DSP), produced by Dinophysis species and concentrated in shellfish by filter feeding, are now routinely monitored by the Washington State Department of Health (WDOH) since the confirmed human illnesses in 2011. The emergence of this new threat to public health had an immediate impact on the Jamestown S’Klallam Tribe whose subsistence and commercial shellfish beds are located near the site where the DSP events occurred from consumption of toxic mussels. In 2012, a collaborative research project was initiated together with the SoundToxins partnership, to determine whether routine monitoring Dinophysis abundance could provide an early warning of concentrations of DSTs accumulated by shellfish. Weekly sampling illustrated that dinophysistoxin-1 (DTX-1) was the primary responsible toxin isomer in WA and that mussels generally concentrated the toxin more than other shellfish. In addition, it was found that D. acuminata was the primary species present during toxic events and increases in cell density often predicted increases in shellfish toxicity. However, surface water samples analyzed from several sites in Discovery Bay did not show elevated numbers of Dinophysis cells as a precursor to DSTs in shellfish. In Sequim Bay, tidal cycle and water depth influenced the abundance of Dinophysis sampled over a 48 h period, demonstrating the need to optimize sampling protocols in order to successfully detect cells in an early warning mode.