Since the summer of 2013, echinoderms along the Pacific Coast of North America have suffered from a mass die-off. Starting in the Pacific Northwest and moving down the coast, 20 different species of sea stars (commonly termed starfish) have suffered from symptoms that start with lesions and swelling and progress through the loss of their ability to coordinate their multiple limbs. It nearly inevitably ends in the complete degeneration of the organism, which largely melts or dissolves.

Perhaps the most disturbing aspect of the disease is that we've had no idea what caused it. We didn't even know whether it was a response to environmental changes or the end result of a pathogen. Now, researchers have published evidence that a virus may be to blame.

A large team of researchers started by noting that the sea-star wasting disease had spread to some aquarium facilities that draw water straight from the ocean, while those that treated their water with UV light had remained disease free. This suggests a pathogen or chemical agent. The team then obtained material from animals dying from the disease and passed it through filters that should exclude bacteria. When injected into healthy animals, it still triggered sea star wasting. Heat treating this material eliminated its ability to cause disease.

This strongly suggests a virus is involved. This was further supported by the fact that material obtained from the newly infected animals could pass the disease on to another round of starfish. Electron microscope images also showed a virus in the material.

But which virus? Lots of viruses are endemic to echinoderms, and even more are found in seawater. The authors sequenced DNA from infected and uninfected animals, both in their facilities and in the wild. Here, the results were less clear-cut. Suspicion focused on one virus because it is generally correlated with infection, and its levels go up as infection progresses. But there wasn't a one-to-one relationship, so the results are only highly suggestive.

The virus belongs to a large family called the Parvoviruses, which also causes disease in dogs and humans, among other animals. Looking through preserved specimens, the authors have been able to find it in sea stars collected as far back as the 1940s. They also note that other instances of sea star wasting disease have been reported around the globe over the last few decades. All of which suggests that, although a virus might be the ultimate cause of the symptoms, something else is likely to be interacting with the virus in order to cause this widespread outbreak.

PNAS, 2014. DOI: 10.1073/pnas.1416625111 (About DOIs).