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.