December 15, 2011

 

 Questions-and cases-mount in seal disease outbreak

 
 
 

Mystery illness killing Arctic ringed seals may be spreading

Seal
An international team of researchers is trying to identify what's behind a disease outbreak
among ringed seals, the most common ice seal in the Northern Hemisphere.
Photos courtesy of NOAA
posted November 30, 2011

A mysterious disease that's killed scores of ringed seals off the Alaskan coast since the summer may also be infecting other species of Arctic marine wildlife.

The outbreak was first reported this July along the North Slope of Alaska. Severely ill and dead ringed seals were found with excessive hair loss and lesions on their faces and flippers. Other signs associated with the disease are delayed molt, lethargy, unusual behavior, and labored breathing.

By late October, government officials had received some 200 reports of sick or dead seals, mostly along the more than 200-mile expanse between the Alaskan cities of Point Lay to the south and Barrow to the north. Approximately 50 animals were dead or died a short time after being found.

Ringed seals are the most common and widely distributed of the Arctic seal species. Since July, ringed seals with the same telltale signs of the mystery illness have been documented in Russia and Canada.

Walruses with similar ulcerative skin lesions are turning up along the North Slope and western coast of Alaska while harp seals with marked hair loss have been sighted in Alaskan waters and around Greenland—indicators the outbreak may not be isolated to ringed seals.

On Oct. 13, the National Oceanic and Atmospheric Administration, one of several U.S. and Canadian entities investigating the outbreak, issued a statement saying it was not known whether the same disease is infecting multiple marine mammal species. Moreover, the agency acknowledged that the cause of the ringed seal illnesses and deaths had so far eluded discovery.

"Laboratory findings have been inconclusive to date, and scientists have not yet pinpointed a single cause of this disease," NOAA explained. "A group of international wildlife researchers continue to test for a wide range of possible factors, including bacterial, viral, fungal, or toxic agents that may be responsible for the animals' condition."

Samples have so far tested negative for poxvirus, parapoxvirus, herpesvirus, papillomavirus, morbillivirus, and calicivirus and are currently being tested for influenza virus.

Native communities living in the region hunt ringed seals and other marine mammals for food, and government officials are advising them against eating sick animals or feeding the meat to their dogs.


Clinical signs associated with the illness include skin ulcers and
lesions, pictured here on a seal's flippers and around another seal's eyes.

Dr. Kathy Burek, owner of Alaska Veterinary Pathology Services in Eagle River, began assisting in the disease investigation this August. As of early November, Dr. Burek had performed necropsies on 10 ringed seal carcasses recovered from the North Slope.

The board-certified veterinary pathologist described the case animals as having excessive hair loss across their bodies as well as ulcerative and erosive lesions on their skin and inside their mouths. In all the seals, one or more pathologic abnormalities have been identified, including hepatitis; vasculitis and thrombosis in the skin, lungs, and spleen; lymphadenopathy; and lymphoid depletion.

Some features of the histopathologic and epidemiologic findings, such as unusual vacuolar changes, possible inclusions in the skin lesions, and a lymphoplasmacytic necrotizing hepatitis, could indicate a virus is behind the outbreak, Dr. Burek explained, hence the intense search for a primary viral etiology.

Dr. Burek has also seen signs suggestive of disseminated intravascular coagulation, including evidence of hemolysis and an unusual bleeding tendency in affected animals that were still alive. And, although vacuolar changes were evident in the cerebral and cerebellar white matter of two carcasses—a possible explanation for the abnormal behavior—Dr. Burek says further testing is necessary to determine whether the condition occurred while the animals were alive or after they had died.

Dr. Burek can't say with certainty what killed the seals, but she suspects the animals were terminally septicemic. "It's not entirely clear what the cause of death is, but septic shock appears most likely, considering the lesions as well as the isolation of a variety of different bacteria systemically from these animals," she said.

Alopecia and delayed molt have been observed in ringed seals around Alaska for the past couple years, according to Alaska State Veterinarian Bob Gerlach. He worries the recent cases of morbidity and mortality, along with the possibility other marine mammal wildlife in the Arctic are infected with the same agent, are signs of a more serious issue.

"This may not just be a problem for a specific species of marine mammals," Dr. Gerlach said, "but could be a reflection of a larger problem across the entire Arctic coastal ecosystem."

Dr. Gerlach and others involved in the investigation speculate that no single infectious agent or toxin is responsible for the outbreak. Rather, they wonder whether the animals are succumbing to a complex combination of stressors brought on by changes in their environment, such as warmer air and ocean temperatures and a diminished sea ice habitat.

But determining how the warmer Arctic climate could be a factor in the disease outbreak isn't easy. "The problem is how do you establish any correlation or causation between these particular disease issues and climate change?" noted Dr. Burek, who has written about the subject for the journal Ecological Applications.

Despite the challenges, Dr. Burek believes the possibility cannot be ignored. "Ringed seals are so dependent on the ice, you have to wonder if it's not a part of the problem," she said. "It'd be unrealistic to think it couldn't be."