At last, a publication on the causative agent for sea star wasting syndrome! Several co-authors have written a paper that was published in the Proceedings of the National Academy of Sciences (PNAS), in which the culprit was identified as a densovirus.
The Smithsonian wrote up a nice article summarizing the findings here.
While it remains to be seen why the virus caused such widespread disease this time, at least now researchers have something to focus their work on.