2009-11-07

Until this week, many veterinarians asserted that it was a myth that house cats could catch the deadly H1N1 flu from their owners.

Those veterinarians, along with other health experts, are revising their views after an Iowa Department of Public Health announcement Wednesday that the virus has been confirmed in an indoor 13-year-old cat, which likely contracted the illness from two flu-sick humans in its home.

Although all of the victims have since recovered, this latest H1N1 animal case puts the focus on humans as the primary carriers of the illness, which experts don't even want to call "swine" flu anymore.

"We're seeing reverse zoonosis, with the virus jumping from people to animals," Alfonso Torres told Discovery News, explaining that several ferrets have also been infected, resulting in at least one pet ferret death in Nebraska.

"In theory, cats could infect humans, but there is no evidence for that yet," added Torres, former chief veterinary officer of the United States who is now associate dean for public policy at Cornell University's College of Veterinary Medicine.

Torres was "not entirely surprised" by the diagnosis in a cat. He said that until four years ago, no evidence supported that felines could catch viruses from other species.

That changed when several captive tigers and leopards died after consuming chickens infected with avian flu (H5N1). A later study concluded that house cats could also contract avian flu.

While no dog has yet been diagnosed with H1N1, a deadly canine influenza strain has led to outbreaks among dogs since the first reported case in 2004. Canine influenza arose when a horse virus, H3N8, infected a dog.

It is not yet clear why ferrets and cats may be more susceptible to H1N1 flu, but Torres explained that "viruses need receptors" to enable infection of an individual. Sometimes these receptors are located in the throat and nose, while other times they are located more deeply in the lungs.

It could be that the anatomy of pigs and ferrets means that their receptors more closely match those of humans for H1N1. It's possible that cats have similar receptors, but further studies are needed to better understand the virus in felines and how to best treat it.

"The human H1N1 vaccine may or may not work in cats," Torres said. "There are some 60 million cats and only the one reported case, so the risk of other cats becoming infected appears to be low at this point."

Since both the avian and "swine" influenza strains emerged under crowded farming conditions, Torres suspects the growing worldwide demand for meat could be setting the stage for such outbreaks. It's predicted that meat production will increase by 50 to 60 percent by 2020 in response to human population growth and economic changes in developing countries.

However, animals and humans living together in close proximity is only one probable factor that could lead to such outbreaks. Increased travel, more pets, climate change and better diagnostic techniques could also help to explain the rash of interspecies illness, he said.

Michael San Filippo, a spokesperson for the American Veterinary Medical Association, told Discovery News that the cat H1N1 case "provides a good reminder that viruses can pass from humans to animals."

While both he and Torres wonder if the Iowa cat suffered from an underlying health condition that might have compromised its immune system, particularly because of the cat's advanced age, they still advise all pet owners to take precautions if they come down with influenza.

"Avoid direct contact with pets if you have the flu," San Filippo said. "Keep them off of your bed and be sure to cover up coughs and sneezes. Wash your hands regularly."

He concluded: "Pets are members of our families, so exercise the same precautions that you would for other friends and family."

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