A polar bear at the Toronto Zoo had to be euthanized after likely contracting West Nile virus from a mosquito bite, zoo veterinarians believe.

If confirmed, they think it would be the first known case of a polar bear contracting the ailment.

Kunik, one of two polar bears at the zoo, began having trouble using his hind legs Sept. 19 and was put down for humane reasons two days later.

The 545-kilogram bear, one of the facility's most popular attractions for a quarter-century, underwent a post-mortem at the Ontario Veterinary College in Guelph.

"It sure looks like (West Nile) right now," said zoo vet Jean Pare. "It's certainly rare in polar bears. We've never seen it before, that's for sure."

The 26-year-old polar bear was euthanized after its back legs became paralyzed, likely as a result of encephalitis, an inflammation of the brain, caused by the virus.

Pare said the first set of blood tests was negative for West Nile, but the post-mortem examination of the bear's brain tissue came up strongly positive.
  
The contradictory test results have cast some doubt on the West Nile diagnosis.
  
But Dr. Ian Barker, who conducted the autopsy in Guelph, said he is confident the bear died of West Nile, although he will send brain samples on to Health Canada to confirm the diagnosis.
  
Barker, a professor of wildlife disease in Guelph, said the bear suffered from the same encephalitic conditions that humans would develop.
  
Evidence of the virus has been found in black bears in New Jersey and in horses, dogs and cats, but there have been only a handful of cases where it actually erupted into the full-blown disease, Barker said.