New Disease Afflicting Sea Otters

Northern sea otters at the Seattle aquarium | Photo: canopic/Flickr/Creative Commons License

A virus related to the ones that cause smallpox and chickenpox has been found in sea otters from California and Alaska, according to researchers at the University of Florida. Though it's unknown just how virulent the virus is, scientists are concerned it could interfere with infected otters' ability to stay warm in the frigid waters of the Pacific Ocean.

The newly discovered poxvirus was isolated from two orphaned sea otter pups being treated in wildlife rehab facilities. Researchers noticed skin lesions on the otters, and isolated an identical virus from the lesions on both animals. As the same strain was found in both the Californian and Alaskan otters, the previously unknown poxvirus is likely widespread through the species' range, at least in the eastern Pacific.

It's unknown whether the new virus poses a threat to humans, though the researchers encourage those working with sea otters in the wild or in rehab facilities to wear protective gear such as gloves. But the potential health risks to the otters themselves are dire enough even in the absence of human health risks.

"To our knowledge, this is the first report of a poxvirus in a mustelid, the group of mammals including otters, mink, badgers and related species," said James Wellehan, assistant professor at the University of Florida's College of Veterinary Medicine, in a University press statement.

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Unlike other marine mammals that insulate themselves from cold seawater with a thick layer of fat, sea otters -- Enhydra lutris -- keep warm with a thick layer of nearly waterproof fur, which provides both insulation and a bit of buoyancy. That fur, the thickest of any mammal's, nearly proved the species' undoing. Once numbering in the hundreds of thousands, sea otters were hunted to the verge of extinction by the dawn of the 20th Century to supply the fur trade.

Hunting mostly ended in 1911 with the signing of the international Treaty for the Preservation and Protection of Fur Seals, though illegal hunting does continue here and there. In the century and change since the Treaty was signed sea otter populations have rebounded. But otter populations in both California and Alaska have plateaued for various reasons, including changes in the marine ecosystems of both areas. In California, exposure to pathogens such as Toxoplasma gondii, spread by domestic cats and opossums, has been implicated in population declines, as have shipping, energy development, and Naval activity.

So this new poxvirus would seem to be the last thing sea otters need. The skin lesions it seems to generate cause fur loss, which means that the sea otters' remarkable natural insulation develops holes. That could easily lead to hypothermia and rapid death in infected otters.

That said, it may be that this novel virus poses only a minor risk to healthy otters at present. According to the researchers' article in this month's issue of the Journal of Wildlife Diseases, the two infected pups displayed only "small superficially ulcerated skin lesions," and the authors noted that the virus "did not appear to be associated with systemic illness."

Still, anything that dents otters' protective fur shield is cause for concern. "What keeps sea otters alive in the cold water is their hair coat." Wellehan said. "Anything affecting their hair coat, with its incredible density of fur, is a huge problem for them."

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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