By John Upton
Nearly 18 months into the worst marine epizootic that humanity has ever seen, scientists appear to have found the cause of death. A virus is being blamed for the mass die-off of starfish along North America’s western coastline. Sickened sea stars grow lethargic and their limbs start to curl. Next comes lesions and the shedding of limbs. The body deflates, then melts into puddles of slime and bone-like ossicles. More than a million starfish, coming from at least 20 species, have succumbed. Some local populations of the keystone predators, whose hunting prowess keep populations of plant grazers in check, have been decimated.
Hopes that the new diagnosis will usher forward a cure, however, are about as low as the deep-sea habitat of a brisingida.
Research described Sunday in Proceedings of the National Academy of Sciences blames the heretofore mysterious deaths on a densovirus — a type of virus that typically plagues crabs, shrimp and other invertebrates. The scientists gave the pathogen the name ‘sea star-associated densovirus,’ or SSaDV.
The scientists discovered that loads of the densovirus were higher in sick starfish collected from the wild than in asymptomatic specimens. They also found that exposing lab starfish to the germ “consistently” induced the hallmark symptoms of sea-star wasting disease, while exposing specimens to heat-killed viruses remained healthy.
When the scientists turned their attention to ethanol-preserved sea stars collected as early as 1923, they discovered that the disease has been infecting starfish since at least 1942.
So why would it suddenly turn into such an ecosystem-rattling problem?
That’s just how viruses roll.
“This is the case for many viruses, including HIV and Ebola, which were present in populations since at least the 1930s but only became epidemics in the 1970s and 80s,” said Ian Hewson, an associate professor in Cornell University’s microbiology department, the leader of the recent research.
Perhaps the virus chanced upon a powerful genetic mutation. An improvement to the way it builds capsids, which are shells that protect viruses during their extracellular ventures, might explain its virulence boost.
Perhaps the manifest changes underway in the ocean, where pollution, carbon dioxide and heat are piling up, has weakened the victims’ natural defenses.
The scientists can’t say, yet, which of these factors is to blame. But they do note that large populations of starfish jammed into small habitats appear to be more vulnerable to outbreaks.
They point to a booming sunflower seastar population prior to the first large outbreak.
“We speculate that the current disease event has been exacerbated by an overpopulation of adult sea stars in the Salish Sea immediately prior to the current disease event,” Hewson said. “The Salish Sea was indeed the first population in which the disease was seen; it was noted in June 2013 on the Olympic coast. The first mass mortality occurred in the Vancouver region shortly thereafter.”
That suggests that preventing sea star populations from booming might help protect against future outbreaks. Given that it’s not clear why the Salish Sea population boomed, that’s a daunting task.
Assuming the scientists have accurately identified the cause of the wasting disease, how else could the discovery be used to squelch the current outbreak?
The answer to that question will not fill you with joy.
“Protecting sea stars in nature from an established pathogen, like the virus seen here, is almost impossible,” Hewson said.
Because the virus is so geographically widespread, Hewson said it would be unfeasible and impractical to remove and protect healthy sea stars. “Likewise, inoculating stars against the virus to build resistance would also not be feasible on a large scale,” he said.
Still, the benefits of finally finding the cause of the disease shouldn’t be understated. “The identification of the causative agent of sea star wasting disease enables accurate diagnosis and more effective management,” said University of Washington professor Carolyn Friedman, one of the new study’s coauthors.
For cheerier sea star times, let’s all tune out of reality for just a moment, and tune into the uninfected antics of Patrick — SpongeBob SquarePants’s friend .