Chicago veterinarians are grappling with an outbreak in dog flu the likes of which has never been seen before.

At least five dogs have died and another 1,000 have been infected with canine infectious respiratory disease, or H3N8, in the Chicago area within recent weeks, CBS News reported.

"It's almost an epidemic," Dr. Jerry Klein, supervising veterinarian at the Chicago Veterinary Emergency Center, told the station. "I've been here for 35 years, it's probably the worst type of outbreak I've ever experienced."

Animal boarding businesses like PetSmart and pet hotels have shut down their Chicago area locations to be disinfected after dogs became sick with the fast-spreading virus, which does not affect humans. Veterinarians say dogs can catch the illness through physical contact with infected dogs at kennels, dog parks and grooming facilities.

Experts warn dog owners to avoid places where dogs gather and to monitor their animals for symptoms.

"The common symptoms include cough, a runny nose, and fever," PetSmart spokesman Andy Izquierdo told CBS Chicago. 

But detecting signs of the virus is difficult as symptoms can take up to 10 days to appear, Terry Medinger, medical director of VCA Aurora Animal Hospital, told the Aurora Beacon News.

Medinger said within two weeks they have gone from treating one dog flu case a week to up to three cases daily. At the Chicago Veterinary Emergency Center, Klein said they treat 15 cases of dog flu a day.

"We have had a few fatalities, so that's why it's exceedingly serious," Klein told CBS News. "It causes pneumonia, in some cases, and some of these dogs have to be on oxygen and on ventilation."

Dog flu may be highly contagious, but it's also highly treatable with a vaccine, which can cost about $100.

"We have had a rush of pet owners having their dogs vaccinated now," Medinger told the Beacon News.

"The good news is we haven't seen the flu mutate. It is not doing what the human virus does."