NBC News (emphasis added): Scientists may have fingered the culprit responsible for a mysterious epidemic that has killed millions of starfish… “Their disappearance is an experiment in ecological upheaval the likes of which we’ve never seen,” Ian Hewson, a professor of microbiology at Cornell University, said… Hewson and his colleagues noted that the disease was a relatively common parvovirus found in invertebrates that rose to epidemic levels due to overpopulation, a genetic mutation or other unknown environmental factors.

PBS: Scientists… said it’s a virus that’s different from all other known viruses infecting marine organisms [and] don’t yet know what sparked the seemingly benign virus to transform into the perpetrator of what’s considered the largest marine disease outbreak ever…

National Geographic: The virus [is] quite common. [Hewson said] “It’s been around for 70 years [and] probably present all over the world.”… Why such a pervasive virus is suddenly killing millions of animals is still up for debate… Previous events [were in] one or two species, but the virus is now infecting 20. It’s unusual for a single type of virus… But mutations in a key part of a virus… can help the infection spread to more species, the study authors write…

Hewson: “It is very peculiar to find a virus [infecting] such large numbers of species.”

Reuters: The researchers detected it in… specimens from as early as 1942. They said it may have been present at low levels for years and only recently became a large-scale threat due to some kind of viral mutation, environmental trigger, starfish overpopulation or other factor.

AP: Hewson adds they don’t know yet what triggered the outbreak of the virus… He said it could be related to… a change in the virus, or changes in the environment.

National Geographic: [Hewson] suspects that the virus may not actually cause the symptoms… [it may] disrupt the sea stars’ ability to control the bacteria that they normally co-exist with… Why is the current outbreak… so dramatic when [virus] is actually an old presence?

• Dr. Pete Raimondi, study author: “Something may have happened recently that caused [virus] to go rogue, because we’ve never seen anything like current outbreak“
• Amanda Bates, Univ. of Southampton: “[The virus] has been living with sea stars for over seven decades without causing the large-scale mass mortality of the past two years… we still don’t know why such a large number of sea stars over such a wide geographic area have succumbed to this disease. Has the virus changed to be more virulent, or deadly? Perhaps something in the environment has shifted.”
• Dr. Mike Murray, Monterey Bay Aquarium: “It provides a… place to start and say, ‘OK, we found this virus in lots of sea stars. What was the trigger? What started it all off? Are there other problems in other species? [This] may or may not have a human basis”
• Dr. Ian Lipkin, Columbia Univ., pathogen discovery specialist: “The authors… note themselves, there is much more work to be done before we will know whether the densovirus they describe is necessary and sufficient to cause disease.”
• Vincent Racaniello, Columbia Univ. virologist: “The crucial experiment that remains… is to… inoculate [the virus] into sea stars, and show that it causes wasting disease.”
• Drew Harvell, Cornell ecologist: “The million-dollar question in all this: Why now? What is it that changed that created the conditions for this outbreak? And we don’t have the answer to that. But certainly a viral mutation would be one explanation.”
• Carol Blanchette, Univ. of Santa Barbara: “It is likely that… environmental causes… have played an important role [and the virus] may only be one part of the story.”
• Watch an interview with lead author Hewson here