With the flu season ready to hit its usual peak in November, health experts are growing increasingly concerned about people passing illnesses on to their pets.

The deadly H1N1 virus of recent years is of particular concern, with humans more likely to be the carriers and our pets the victims.

PHOTOS: Seeking A Friend For The End Of The World

The journal Veterinary Pathology, for example, documented how an Oregon woman became severely ill with the flu and had to be hospitalized. While she was still in the hospital, her cat — an indoor cat with no exposure to other sick people, homes, or wildlife — died of pneumonia caused by an H1N1 infection.

Since then, researchers have identified a total of 13 cats and one dog with pandemic H1N1 infection in 2011 and 2012 that appeared to have come from humans. Pet ferrets have also been shown to be infected, and some died. All of the animals’ symptoms were similar to that of humans – they rapidly develop severe respiratory disease, stop eating and some die. Serological studies suggest there is far more exposure to flu virus in cats and dogs than previously known. (As reported in an Oregon State University press release)

WATCH VIDEO: How far can a human cough? Find out.

"We worry a lot about zoonoses, the transmission of diseases from animals to people," Christiane Loehr, an associate professor in the OSU College of Veterinary Medicine, said in the release. "But most people don't realize that humans can also pass diseases to animals, and this raises questions and concerns about mutations, new viral forms and evolving diseases that may potentially be zoonotic. And, of course, there is concern about the health of the animals."

NEWS: How Swine Flu Can Become Pandemic

"It's reasonable to assume there are many more cases of this than we know about, and we want to learn more," Loehr added. "Any time you have infection of a virus into a new species, it's a concern, a black box of uncertainty. We don't know for sure what the implications might be, but we do think this deserves more attention."

The phenomenon is called reverse zoonoses. About 80-100 million households in the United States have a cat or dog, so the situation could turn into a disaster should viruses mutate to infect another species. Human influenza viruses are frequently isolated from birds and pigs. That could be because these animals, often raised for food, are tested more.

NEWS: Can Humans Infect Pets with H1N1?

"All viruses can mutate, but the influenza virus raises special concern because it can change whole segments of its viral sequence fairly easily," Loehr said. "In terms of hosts and mutations, who's to say that the cat couldn’t be the new pig? We’d just like to know more about this."

Image: Bluetick Hound (Dale Spartas, Corbis)