Falling Stars: Probing the Starfish Pandemic

Sea-star wasting disease (SSWD) is a recurring phenomenon whereby massive numbers of starfish die on the American West Coast; this baffling occurrence has been tracked for nearly a century without a convincing explanation. SSWD is a merciless malady, leading to a variety of effects including deflation, self-amputating limbs, and a corrosive death that scientists have dubbed “melting.” Previous studies propose storms, fluctuating temperatures, and starvation as probable causes for SSWD, but a recent report from Ian Hewson’s lab at Cornell University has found a different answer: a virus.

Hewson and his collaborators noticed that SSWD seemed to be contagious, for in the 2013 epidemics, sites of infection moved up the Pacific Northwest coastline. Further environmental analysis of these waterways led the team to discover that starfish living in water that received large amounts of UV light were healthy, whereas regions with unfiltered or sand-filtered inflow tended to harbor infected organisms. These patterns suggested a water-borne microbe rather than an environmental cause. To test that theory, the researchers collected SSWD-infected sea-stars, homogenized them, and then filtered that material through virus-sized pores. Healthy sea stars injected with this material developed SSWD within a few weeks, and repeat experiments with those freshly infected starfish produced the same result.

To identify a candidate virus, the team performed surveys of healthy and infected starfish to understand wildtype and SSWD starfish microbiomes. From this data, they were able to assemble a new viral genome, which they have named sea star-associated densovirus (SSaDV). A comparison of the SSaDV genome to 72-year-old museum specimens collected during historic sea star wasting disease pandemics showed that SSaDV could have been infecting starfish for decades. The researchers suggest that the warming seas might be the cause for the increased host susceptibility and rates of transmission in recent years.