Abstract

Sea Star Wasting Disease (SSWD) is associated with one of the largest marine wildlife die-offs ever recorded, killing millions of sea stars from Alaska to Mexico since the summer of 2013.¹ During the initial 6 months of the SSWD epizootic, many captive Asteroidea at the Seattle Aquarium became moribund with mortality rates in common species such as Pycnopodia helianthoides reaching 100%. Over 20 species of sea stars have been affected by SSWD along the west coast, with Pycnopodia, Pisaster, Evasterias, and Orthasterias the most documented genera in terms of impact. The etiology, contributory factors and pathogenesis of this disease process are actively under investigation. Anecdotal reports suggested that enrofloxacin administered via intracoelomic injection (IC) was effective in treating SSWD in captive sea stars.

Fifty-two stars from the four commonly affected genera listed above and the Dermasterias genus (Dermasterias imbricata), all showing early signs of SSWD, were randomly assigned into a treatment group (n = 26, enrofloxacin 5 mg/kg, IC q 4 days) and a control group (n = 26, saline 0.9%, IC q 4 days) for a total of six treatments. Animals were monitored and graded for severity of lesions twice daily. The scores were not significantly different between groups throughout the study period. At day 20, after four treatments, the mortality rate was 100% and 77% in the control and treatment groups, respectively, and was not significantly different (p = 0.55). At 30 days, after six complete treatments, the mortality rate in the treatment group was 95% and there was no significant difference between the two groups (p = 0.9). A complete necropsy was performed on all mortalities, and samples were submitted for histopathology. An unexpected and notable occurrence at several points during the study period was the presence of pedicellariae from species in the Asteriidae on the external surface of D. imbricata. The removal of pedicellariae from D. imbricata and complete separation of D. imbricata from Asteriidae sea stars resulted in the resolution of SSWD clinical signs in affected animals. Enrofloxacin given intracoelomically at 10 mg/kg to sea stars results in high drug concentrations in the hemolymph of sea stars (J. Rosenburg, pers. comm.). However, administration of enrofloxacin by injection did not alter mortality rates significantly in captive sea stars affected by SSWD and is therefore not recommended for the treatment of this disease in commonly affected species

Acknowledgments

The authors would like to thank Dr. Martin Haulena of the Vancouver Aquarium and Dr. Michael Murray of the Monterey Bay Aquarium for their support and review of this project. The authors would like to thank the Boeing Corporation for their generous support of Sea Star Wasting Disease research through a grant awarded to the Seattle Aquarium.

* Presenting author
⁺ Student presenter

Literature Cited

1.  Hewson I, Button JB, Gudenkauf BM, et al. Densovirus associated with sea-star wasting disease and mass mortality. PNAS. 2014;111(48):17278–17283.