Starfish on the Pacific coast of North America wither away and die since June last year and in a new research, scientists said that the phenomenon is caused by a virus.
The sea stars that have wasted away into nothingness is struck by what is known as the sea star wasting disease, or SSW, which causes sea stars to disintegrate as their limbs pull away.
Although scientists are aware of this disease for a long time, the outbreak that has been going on for a year and a half now is unprecedented given its geographical extent affecting species of starfish along the Pacific from Mexico to Alaska and for reason that it afflicted about twenty species of asteroid sea stars.
Once infected by the disease, the starfish's arms curl from the tips and tie themselves into pretzel-like knots. The normally plush body of the starfish then starts to deflate and white lesions appear on the skin. As these sores spread, the flesh of the animal starts to rot away and their arms fall off. In just a matter of days after the symptoms start, healthy starfishes disintegrate and die.
Marine biologists had several ideas on what could possibly be causing the large-scale deaths of sea stars. This includes global warming, storms and pollutants. Now, a new study published in the Proceedings of the National Academy of Sciences on Nov. 17, offers evidence of what has been causing the death of millions of asteroid starfish.
Study researcher Ian Hewson, from the Department of Microbiology at the Cornell University in Ithaca, New York, said that prior to the research, scientist know little about pathogens of sea stars but the study reveals that a virus that has been sweeping starfishes is the likely the culprit behind the marine animals' death.
For their study, Hewson and colleagues blended the tissues from disintegrating starfish and then passed these through filters with pores small enough so bacteria won't get through but large enough to allow viruses to pass through.
When the researchers injected healthy starfishes with the extract, the animals begin wasting away in just a few weeks. Notably, the extracts did not harm the animals if these were boiled prior to inoculation confirming that the disease is transmissible and is caused by virus-sized organism.
By sequencing the extract that killed healthy starfishes, the researchers found that it contains the genome of the sea star-associated densovirus (SSaDV). They also found that animals that show symptoms of the disease were more likely to carry SSaDV compared with healthy starfishes. Hewson and colleagues also found that symptoms tend to be worse when there is a higher number of SSaDV.
"SSaDV loads were more abundant in symptomatic than in asymptomatic asteroids," Hewson and colleagues wrote. "SSaDV could be detected in plankton, sediments and in nonasteroid echinoderms, providing a possible mechanism for viral spread."