Scientists have identified the probable cause of a disease that devastated starfish along the west coast 'North America. Detective work experiences and genomic laboratory show that the wasting disease is associated with a previously unknown virus. With the discovery comes a deeper mystery, however. Virus-kill sea star is far from new. The study authors found in museum specimens up to the age of 72 years, scientists are puzzled about why the current outbreak has been so severe.
"This is probably the most extensive and devastating disease of marine invertebrates happened," said ecologist Bruce Menge at Oregon State University, Corvallis, who was not involved in the new research. "It is a major concern."
The enigmatic disease came to widespread attention in June 2013, when recreational divers near Vancouver, British Columbia, and Seattle, Washington, began notice the legions of dying starfish. first starfish developed lesions, and then began to lose their arms, and finally decayed into piles of skeletal ossicles (bits of calcium carbonate, such as plates and spines a star). as the year progressed, the disease has been observed in more and more places in the waters off California.
Although there have been minor outbreaks in previous decades, it is much more widespread, and more than 20 species of sea stars were afflicted other types of echinoderms, the animal group to which starfish and sea urchins belong, not the not. the researchers ran to collect samples and conduct laboratory experiments to investigate any pathogens that might be involved. A feature in Science earlier this year, now available, examined the mystery.
The scientists sent hundreds of tissue samples to Ian Hewson, microbial oceanographer at Cornell. When sequencing the DNA in the samples, he discovered that densovirus was more frequent in patients than in those stars who looked healthy. (Densovirus are known to infect insects, shellfish and some sea urchins.) Further evidence came from experiments conducted by marine ecologist Drew Harvell of Cornell and other researchers who took tissue starfish sick , filtered whole greater than the virus, and injected into the tissue starfish apparently healthy. They developed symptoms and at the same time, the amount of densovirus in their body has increased. Other starfish injected with sterilized tissue do not develop symptoms of wasting disease.
"We have very good evidence that this is a densovirus" says Hewson. But because the virus can not be grown in culture, scientists can not meet the standard tests to identify the culprit a disease. four criteria collectively called Koch's postulates the researchers published their findings online today in Proceedings of the national Academy of sciences
looking. a historical perspective, Hewson tested starfish museum specimens collected between 1923 and 2010 along the US west Coast. the virus existed in the healthy appearance of samples of five different years, which suggests that he persisted in the environment. Hewson speculate that the virus may have mutated as it wiped out several species of starfish, which allows it to infect others. it is also trying to understand the source of the virus, analyzing the starfish around the world, and if it can infect other types of echinoderms.
The biggest question is why the current outbreak has been so bad. A situation which, Hewson and his colleagues say, is that a starfish overabundance increased transmission of the virus, especially if they were highlighted by the competition for food, which could make them more vulnerable to infection .
This theory is logical Navy pathologist Marta Gomez-Chiarri the University of Rhode Island, Kingston, who was not involved in the new document. She and her students studied an earlier epidemic densovirus on the east coast; starfish populations in Narragansett Bay Rhode Island abounded before an accident in 2011. It is not known if the same densovirus caused the die-off west coast is also implicated in the decline of the East. Hewson found some genes Densovirus sea stars Connecticut, but has not enough samples for definitive conclusions.
Menge do not think the glut played a role in the current epidemic among populations stars 13 Sea follows on the Oregon coast. Instead, he wonders if ocean acidification, which can also be a source of stress that weakens the starfish, is a possible contributing factor. So far, the evidence is mixed for the role of acidification, Menge admits.
Whatever the cause of the outbreak, Menge said, violet stars of disappearance has already led to greater survival of prey, including barnacles and mussels. As a result, he predicted, the molds will eventually take over the rocky coast, the eviction of many other invertebrate species. Somehow, he adds, the epidemic is a unique opportunity in a lifetime to ecologists to study the predator-prey relationships. But it does dull the pain of losing familiar and charismatic species. "From a personal point of view, it is really disheartening."
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