Nothing is more comforting when you're feeling lousy than to curl up with your cat or dog. But if you have the flu, is your pet at risk of getting sick as well?

Unfortunately, the answer is yes. The phenomenon of the ability of humans to pass along illnesses to their pets is called "reverse zoonosis," and it can be fatal. A probable case of human-to-cat transmission of the pandemic H1N1 flu virus occurred in 2009 when a cat caught flu from its owner and died of pneumonia caused by the flu. Since then, other cases have been documented, including dogs, rabbits, and ferrets. One study found that 30 percent of cats tested had been infected with flu.

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"It’s reasonable to assume there are many more cases of this than we know about, and we want to learn more," said Christine Loehr, an associate professor in the Oregon State University College of Veterinary Medicine.

"We worry a lot about zoonoses, the transmission of diseases from animals to people," she said. "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."

The jury is still out on whether or not your pet can catch your cold. According to some experts, dogs can't catch human colds, but cats are at risk, although the odds are very small. Other experts believe that although both cats and dogs can suffer from colds, the viruses are different from the ones that affect humans.

Other diseases you can pass along to your pet include:

• Mumps. Although rare, the mumps virus, caused by a virus that infects the salivary glands, can be transmitted to dogs. In dogs, the disease is called parotiditis.

• Salmonella. Salmonella is a bacterial disease that affects the intestinal tract, and humans are typically infected through contaminated water or food. Pets contract salmonella through the same means.

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• Tuberculosis. A study published in the Journal of the American Veterinary Medical Association found that an owner passed tuberculosis to the pet dog, and another study found that all dogs diagnosed with tuberculosis had contact with an infected person. Although cats can also catch tuberculosis from humans, it is extremely rare.

• MRSA. Numerous cats and dogs have been diagnosed with Methicillin-resistant Staphylococcus aureus (MRSA). A study at the University of Minnesota Veterinary Medical Center found that infected animals either had owners who worked in healthcare, had been hospitalized recently, or were caring for a family member who had been recently hospitalized.