Seal disease investigation intensifies

Published on February 01, 2012
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The investigation into a fatal disease among ringed seals in the Arctic and Bering Strait regions of Alaska has intensified following a federal agency's determination the outbreak constitutes an "unusual mortality event."

The decision by the National Oceanic and Atmospheric Administration this past December means additional resources will be dedicated to identifying what's behind the illnesses and deaths of more than 100 seals since the summer (see JAVMA, Dec. 15, 2011). As of press time in January, the U.S. Fish & Wildlife Service had not determined whether it would declare the outbreak an unusual event.

More than 60 dead and 75 diseased seals, mostly ringed seals, have been reported in Alaska since July 2011, with reports continuing to come in. USFWS scientists have also identified diseased and dead walruses along Point Lay in northwest Alaska. 

ringed seal with facial lesions
Facial lesions are a common sign of a mystery illness afflicting 
ringed seals along the Alaskan coast. (Courtesy of North Slope
Borough Department of Wildlife Management)

Federal law authorizes the allocation of additional personnel, finances, and other resources in response to incidents involving unusually high mortality rates among marine mammals. Fifty-five unusual mortality events have been formally recognized in U.S. waters since the program was started in 1991.

Seals and walruses suffering from the mystery disease develop skin sores, usually on the hind flippers or face, and patchy hair loss. Some of the diseased mammals have labored breathing and appear lethargic.

Scientists have not yet identified a single cause for this disease, although tests indicate a virus is not the cause.

At necropsy, most of the affected animals have had skin lesions as well as fluid in the lungs, white spots on the liver, and abnormal growths in the brain. Some seals and walruses have undersized lymph nodes, which may indicate compromised immune systems.

Testing continues for a wide range of possible factors that may be responsible for the animals' condition, including immune system–related diseases, fungi, man-made toxins and biotoxins, radiation exposure, contaminants, and stressors related to sea ice change.

Similar signs have been reported in walruses in Russia and ringed seals in Russia and Canada. Although it is not clear whether these other disease events are related to those in Alaska, the timing and location of the disease incidents suggest the possibility of transmission between the populations, or shared exposure to an environmental cause.

Numerous government agencies and other organizations are involved in the investigation, which, according to NOAA, may require months or even years of data collection and analyses.