Experts blame the epidemic on a strain called H3N2 that is seen in Asia and leaves pets feeling lousy for about two weeks. Veterinarians believe the strain, which doesn't yet have a vaccine, will likely spread to other parts of the country, so they offer ways to keep pets healthy or help those that are already ill.
WHAT TO LOOK FOR
Steve Gilberg, a digital marketer in Chicago, says his 6-year-old pug-Chihuahua mix, Joey, had most of the symptoms: high fever, runny nose, watery eyes, sore throat and loss of appetite. But mostly, he coughed.
"He just started coughing really, really hard, kind of like a smoker's hacking cough, coming from the belly," Gilberg said.
Dr. Brian Collins urges owners to pay attention to changes in behaviour, such as dwindling interest in eating, drinking and playing, laboured or rapid breathing, or lethargy.
"If he's always happy to eat and now he isn't, that isn't a good sign. Are they clingy when they are usually close, removed when they are usually just a bit aloof?" said Collins, a companion animal veterinarian at the Cornell University College of Veterinary Medicine in Ithaca, New York.
HELPING SICK PETS
Start by taking its temperature. You can't just feel your dog's forehead to see if it's running a fever, but digital thermometers can take readings under an armpit or in the most accurate area — the backside, Collins said.
Food and fluids are important, so keep trying to entice your buddy. With a pet that isn't eating well, offer fare that's a bit more tempting, but be careful it doesn't cause a stomachache. Try some baby food, canned meals or dry food softened with water.
Dogs probably have achy muscles, a sore throat and stuffy head, while feeling tired and run down, so don't discourage long bouts of snoozing as long as they are getting up to go outside and staying hydrated.
"If he's mostly resting and seems stable and is breathing comfortably, then the more sleep, the better," Collins said.
Gilberg said his sick pup would lie in bed all day, but it helped to hold him and then his energy returned gradually.
Infected dogs can be contagious for two weeks, so keep pets — sick or healthy — away from other pooches and places where they gather, such as doggie day cares, dog parks, groomers and pet stores.
Some pet businesses in Illinois closed for a few days to help stop the spread. When Gilberg took Joey to the vet, the receptionist asked them to wait out front to avoid getting other dogs sick.
The virus gets passed through the air when dogs sneeze or by people when germs jump on hands or clothing, where they can live for hours. But the canine flu doesn't sicken people.
WHEN MEDICINE HELPS
There is no vaccine for the strain sweeping through Illinois, Wisconsin, Ohio and Indiana. Shots are available for a similar strain seen last year, and some vets believe it could help ward off germs.
But there's no need to vaccinate dogs that are already sick, said Dr. Drew Sullivan of the Medical District Veterinary Clinic at Illinois in Chicago.
Antibiotics likely would come in if a flu-infected dog contracts pneumonia.
But doctors warn against treating dogs with cough syrup or other over-the-counter medicine in case it counteracts with other medications.
"I don't think it's going away," Sullivan said of the outbreak. "We can't treat the virus, just the symptoms."