Canadians are lining up for H1N1 shots but their furry friends can't, even though they may also be susceptible to the virus.

On Wednesday, U.S. officials confirmed that a 13-year-old cat was infected with swine flu. The domestic shorthair was treated last week at Iowa State University College of Veterinary Medicine and has recovered.

"This may be the first instance where we have documentation that transmission occurred involving cats or dogs," said U.S. Centers for Disease Control and Prevention spokesman Tom Skinner.

Swine flu was also confirmed in two pet ferrets in Oregon and Nebraska. Stormy, one of four pet ferrets owned by a Nebraska family, died last week after all the animals contracted H1N1 influenza from their owners.

Scott Weese, an expert in zoonotic diseases at the University of Guelph, said the animal cases underscore the need for owners of companion animals to realize that "pets are part of the household microbiologically, not just socially."

Ferrets, which are often used as a research model for infectious diseases in humans, are likely the pets most vulnerable to flu strains.

Pet birds, pot-bellied pigs and felines are also likely susceptible.

Dogs have their own influenza, but there is little likelihood of Fido infecting humans or vice-versa, Weese said.

Equine influenza also doesn't affect humans.

To avoid spreading H1N1 to pets, Weese recommended avoiding close contact, especially face-to-face, and washing hands frequently.

With files from The Associated Press