Atlantic seal virus found in Kachemak Bay otters

Posted: Monday, June 22, 2009

A virus previously seen only in Atlantic Ocean seals has been identified in Alaska sea otters, including three dead otters found in Kachemak Bay from 2005-2007. In a paper published this month in the Centers for Disease Control's "Emerging Infectious Diseases," phocine distemper virus was documented in dead and live otters tested by biologists studying an unusual mortality event among Alaska sea otters.

Ocean warming and a decline in Arctic Ocean sea ice may have lead to the spread of the virus across the Arctic.

The phocine distemper virus, or PDV, is suspected to be the cause of an unusual number of sea otter deaths in Alaska, including Kachemak Bay, said Verena Gill, a U.S. Fish and Wildlife Service marine mammal biologist, and one of the authors of the report, "Phocine Distemper Virus in Northern Sea Otters in the Pacific Ocean, Alaska, USA," by Tracy Goldstein, Jonna A.K. Mazet, Gill, Angela M. Doroff, Kathy A. Burek and John A. Hammond.

Those otters died of what scientists are now calling "strep syndrome," or a streptococcus bacterial infection. Gill, Doroff and Burek, all Alaskans, have done much of the research on dead otters found stranded in Kachemak Bay. Necropsies showed 43 percent of dead otters found had valvular endocarditis and septicemia, conditions that lead to heart valve defects and eventual death and associated with strains of streptococcus infantarius, a bacterial infection. The strep caused the disease, but what caused the otters to become susceptible to strep? That's the question that led to the new finding.

A veterinarian the scientists consulted said that if a dog had valvular endocarditis, vets would diagnose canine distemper, a disease present in Alaska that sometimes gets into the marine environment. The otter scientists tested tissue samples from dead otters looking for canine distemper.

"We were surprised when it came back negative for canine but positive for phocine distemper," Gill said.

"For sure right now we can't say it's causing this strep syndrome, but it's the leading culprit," she added.

PDV is not necessarily the cause of strep syndrome, though, and more research needs to be done.

PDV caused two epidemics in northern Europe, killing 23,000 harbor seals in 1988 and about 30,000 more in 2002. It also was associated with seal deaths on the east coast of Canada and the United States.

"The reason we published the report was PDV has never been found in the Pacific," Gill said. "Now we're going to see how widespread it is."

PDV probably spread over the Arctic Ocean during periods of decreased sea ice caused by ocean warming. The 1988 Atlantic PDV virus did not reach Alaska. Reduction of sea ice was pronounced in 2004 and 2005, years in which PDV infected otters here. Several seal species have ranges overlapping between the Pacific and Atlantic oceans. Sea ice reduction may have altered seal haulout and migration patterns, resulting in contact between Atlantic, Arctic and Pacific ocean species, the authors write.

With PDV found in the Pacific Ocean, there is a potential for it to infect western marine mammals.

"All seal species in the Arctic and Pacific Oceans are threatened, especially those with limited numbers, and epidemic management strategies must be in place to protect critically small populations," the authors caution.

There is a vaccine for PDV, Gill said. Seals captured for rehabilitation in the United Kingdom are routinely vaccinated. Scientists in Hawaii are considering vaccinating the endangered monk seals if PDV spreads there.

More testing of Pacific Ocean marine mammals for PDV is going on this summer. Goldstein, the lead author, is sampling seals and polar bears in the Arctic this summer. PDV is shed through the nose, and its presence can be tested through nasal swab samples.

The report is available online at Gill and Doroff work with the U.S. Fish and Wildlife Service, Anchorage, and Burek is with Alaska Veterinary Pathology Services, Eagle River. Goldstein and Mazet work with the University of California at Davis and Hammond with the Stanford University School of Medicine, Stanford, Calif.

Michael Armstrong can be reached at

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