Along the Pacific coast of North America, sea stars have been dying off in record numbers since June 2013. The cause of sea star wasting disease, which transforms the animals into piles of mush, has been difficult to pin down. A study published this week (November 17) in PNAS points to a probable culprit: a single-stranded DNA virus known as a densovirus, related to viruses found in Hawaiian sea urchins.

Inspections of hundreds of infected tissues turned up no evidence of bacterial or eukaryotic pathogens, which led researchers to suspect a virus. A team led by scientists at Cornell University filtered extracts from sick sea stars to eliminate any infectious agents larger than viruses. They found that this filtrate caused healthy animals to develop the disease.

“When we inoculated them, they died within about a week to 14 days,” Cornell microbiologist Ian Hewson told Oregon Public...

Sequence analyses uncovered the densovirus, which turned out to be present in museum specimens dating back as far as 1942. Although sea star wasting disease has been observed in the past, this is the first time it has spread this widely and to such a range of species—at least 20 different taxa.

“This is probably the most extensive and devastating disease of marine invertebrates that has happened,” ecologist Bruce Menge of Oregon State University told Science. “It’s a major concern,” added Menge, who was not involved in the study.

The die-off has already led to increased populations of the sea stars’ prey, including barnacles and mussels, in many coastal areas. Researchers are continuing to examine whether factors such as increased ocean temperatures and acidification might contribute to the spread or severity of the disease.

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