Scientists fear Canadian polar bears may be threatened by the spread of avian flu after officials confirmed the disease killed a bear in Alaska.

SA国际影视传媒淭hereSA国际影视传媒檚 a very high likelihood that it is (in Canadian bears),SA国际影视传媒� said Andrew Derocher, a leading polar bear biologist at the University of Alberta. SA国际影视传媒淚tSA国际影视传媒檚 there. We just arenSA国际影视传媒檛 looking for it.SA国际影视传媒�

Last month, officials with the U.S. Department of Agriculture confirmed the H5N1 strain of avian flu killed a polar bear, found in October near the Alaskan town of Utqiagvik about 500 kilometres from the Yukon border. Polar bears range hundreds of kilometres and the dead bear was part of a population shared by both countries.

The virus first showed up in Yukon more than a year ago in a red fox, said territorial veterinarian Jane Harms.

SA国际影视传媒淭his strain of avian flu seems to have the ability to infect and cause disease in mammals of a variety of types,SA国际影视传媒� she said. SA国际影视传媒淭he fact this virus can cause disease and death in polar bears, as well as other species, is of concern.SA国际影视传媒�

ItSA国际影视传媒檚 not clear yet how far the virus has spread among Arctic mammals. Alaska has found it in red foxes, a black bear and a Kodiak bear.

Harms said it seems so far it is being spread when mammals eat infected birds.

SA国际影视传媒淚n most cases, wild mammals are being infected by scavenging tissues of infected birds. It does not seem to be transmitted mammal to mammal.SA国际影视传媒�

But Derocher said climate change is likely increasing the bearsSA国际影视传媒� exposure, as diminishing sea ice keeps them on shore longer and forces them to subsist on prey such as dead birds. Those extended shorebound periods of relative scarcity also weaken the bears.

SA国际影视传媒淚mmune system function goes down. With weakened immune systems, theySA国际影视传媒檙e more likely to succumb.SA国际影视传媒�

As well, polar bears are more vulnerable to viruses than other bears, said John Whiteman, chief researcher at Polar Bears International and professor at Old Dominion University in Virginia. While evolving for the Arctic, they lost much of their genetic SA国际影视传媒渓ibrarySA国际影视传媒� of possible pathogens and how to resist them.

SA国际影视传媒淚f you can recognize a lot of pathogens, youSA国际影视传媒檙e in better shape to fight them off,SA国际影视传媒� said Whiteman. SA国际影视传媒淧olar bears donSA国际影视传媒檛 recognize a lot of pathogens.SA国际影视传媒�

Climate change has stirred the pot on viruses around the world, he said.

SA国际影视传媒淲e know that pathogens are changing their distribution and some of them that may not have been able to survive the north slope of Alaska are gaining a foothold.SA国际影视传媒�

Avian flu is now found on every continent except Australia.

Both Whiteman and Derocher called for better monitoring of wildlife diseases.

Harms said Yukon regularly performs necropsies on dead wildlife, but more needs to be done. Confirming avian flu requires extra testing, she said.

SA国际影视传媒淭he reality is we probably would have more avian flu virus infection in mammals if we had the ability to look for it.SA国际影视传媒�

The Southern Beaufort population of which the dead bear was a member is estimated to be about 900 strong, although itSA国际影视传媒檚 hard to be sure with polar bears. That population is considered to have declined by about 50 per cent since the 1980s, said Derocher.

The virus has hit other mammals hard. Scientists have linked it to the deaths of nearly 500 seals in Maine over the last two years.

But both Derocher and Whiteman say one bear death isnSA国际影视传媒檛 enough to push the virus panic button.

SA国际影视传媒淚 would put it in the category of a little alarming,SA国际影视传媒� said Whiteman. SA国际影视传媒淭his threat still has so much unknown to it. But there is a potential for mortality.

SA国际影视传媒淏y far, the biggest threat to this species is the loss of sea ice.SA国际影视传媒�

SA国际影视传媒擝y Bob Weber, The Canadian Press