Abstract

A large-scale mortality event affecting at least 20 species of sea star (Asteroidea) on the Pacific coast of North America began in June of 2013 and continues to present (January 2015). An international, multidisciplinary and multi-institutional team of investigators is participating in the ongoing efforts to determine the cause of this unusual wildlife mortality event.

First detected in ochre sea stars (Pisaster ochraceus) along the outer coast of Washington State, Sea Star Wasting Disease (SSWD) has now been observed in wild populations at more than 240 subtidal and intertidal locations from southeastern Alaska to southern California, and at least five Pacific coast public aquaria that utilize 'open' water systems. Pisaster, Pycnopodia and Evasterias are the most well-documented genera in terms of impact, and mortality approaches 100% in select species at some locations. Short-term repeated sampling at select field sites suggests the disease often begins in one species and affects sympatric species over time in a predictable order. Clinical signs include: 1) loss of body turgor (deflation) and weakness; 2) foci of body wall pallor and tissue loss; 3) sloughing of multiple rays and/or rupture of the body wall with evisceration; 4) death.

Samples of affected and unaffected sea stars from captive and wild populations in Alaska, Washington, Oregon, California and British Columbia were collected for pathologic (n = 147) and molecular (n = 335) investigation. To date, 14 asteroid species have been examined histologically by members of a SSWD pathology working group. Consistent histologic changes include: 1) epidermal degeneration, necrosis and ulceration; 2) dermal edema, necrosis and inflammation. Comparative body wall composition analysis and mineral staining were also pursued to investigate the pathogenesis of the clinical body wall dissolution. Community fingerprinting and bacterial metagenomics identified three candidate disease-associated bacterial phyla including Bacteroidetes, Gammaproteobacteria and Spirochaetes. Viral metagenomics identified several candidate disease-associated metazoan viruses including a sea star-associated densovirus (Parvoviridae).¹ Transmission trials utilizing virus-sized filtrates of tissue homogenates from symptomatic animals resulted in clinical signs of SSWD in asymptomatic animals. Links between the histologic lesions and candidate disease-associated organisms identified by viral and bacterial metagenomics remain under investigation by transmission electron microscopy and in situ hybridization. Investigations of contributory environmental factors to SSWD development and population recovery are ongoing.

Acknowledgements

The authors would like to thank all collaborators including additional members of the Sea Star Wasting Disease Pathology Working Group: Dr. Michael Garner, Northwest ZooPath; Elise LaDouceur, University of California-Davis, School of Veterinary Medicine; Salvatore Frasca, Jr., University of Connecticut, Connecticut Veterinary Medical Diagnostic Laboratory; Roxanna Smolowitz, Roger Williams University, Aquatic Diagnostic Laboratory; Thierry Work, U.S. Geological Survey, National Wildlife Health Center - Hawaii Field Station; Susan Knowles, U.S. Geological Survey, National Wildlife Health Center; Mark Stidworthy, International Zoo Veterinary Group. Additional members of the Hewson Laboratory: Jason B. Button and Brent M. Gudenkaff. Additional members of the Raimondi Laboratory, University of California-Santa Cruz: Monica Moritsch, Rani Gaddam, Melissa Renfield. Additional members of the Harvell Laboratory, Cornell University: Colleen M. Burge, Morgan Eisenlord. Benjamin Miner, Western Washington University, Department of Biology. Michael Frenock, Oregon State University. Members of the Wessel Laboratory, Brown University: Gary Wessel and Vanesa Zazueta. Additional Pacific coast veterinary collaborators: Michael Murray, Monterrey Bay Aquarium; Tim Miller-Morgan, Oregon State University, Oregon Sea Grant; Janna Wynne, California Science Center; Joseph K. Gaydos, University of California-Davis, Sea Doc Society. The members of the Multi-Agency Rocky Intertidal Network: see www.marine.gov for complete list of researchers and affiliations.

* Presenting author

Literature Cited

1.  Hewson I, et al. Densovirus associated with sea-star wasting disease mass mortality. PNAS. 2014;111(48):17287–17283.