Canadians have been lining up across the country to get an H1N1 flu shot, but it may not be just themselves and their family members they have to worry about when it comes to contracting the virus.
Some pets may also be susceptible to the disease.
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.
"We've known certainly it's possible this could happen," said Tom Skinner, a spokesman for the U.S Centers for Disease Control. "This may be the first instance where we have documentation that transmission occurred involving cats or dogs."
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."
"So if you have an infectious disease, you try not to transmit it to your family members, and your pets should be part of that."
Mr. Weese said there are no hard data on which species of pets are vulnerable to H1N1 influenza, which carries a mix of human, avian and swine flu genes.
But he said ferrets, which are often used as a research model for human infectious diseases, are likely the pets most vulnerable to certain flu strains.
"One of the big questions is pet birds and pet pot-bellied pigs," he said Wednesday from Guelph, Ont. "Pet birds and pet pot-bellied pigs would be the next ones I'd be worried about because we know that these are susceptible to influenza."
However, when it comes to the most common pets in Canadian households - dogs and cats - Mr. Weese said felines are likely at higher risk for H1N1 than canines.
"We know that cats are susceptible to some influenza viruses. We know with H5N1 avian flu, cats can become infected, cats can get sick from it and cats can also shed the virus."
Dogs have their own influenza, and there is little concern about Fido infecting humans or vice versa, he said.
Still, "we never say never with an infectious disease," said Mr. Weese. "It's certainly possible."
He said horses fall prey to an equine flu that doesn't affect humans. But then there are all the other animals that people share their domestic lives with - from rabbits and gerbils to reptiles and rodents.
"And we know virtually nothing about a lot of them in terms of their susceptibility to influenza or any other diseases," Mr. Weese said.
The veterinarian who treated the cat in Iowa, Dr. Brett Sponseller, said two of the three people in the home had flu-like symptoms before the feline became ill.
Other influenza strains have been known to cross species, but Dr. Sponseller cautioned against drawing too many conclusions from the cat, including whether other pets could also get the swine flu.
"It's well-documented in influenza in general, but this is the first highly suspected case of H1N1 going from humans into a cat," he said. There is no H1N1 flu vaccine for pets.
Mr. Weese said pet owners should take the same precautions against spreading swine flu to pets as they would with humans - by avoiding close contact, especially face-to-face, and washing their hands frequently.
"It's something we certainly ... something we always say we have to pay a lot more attention to what, what goes on with household pets, because they're the individuals that some people have the closest contact with."
With files from The Associated Press