CHICAGO (CBS) — The dog flu has started to reappear in the Chicago area, and vets say if your dog isn’t vaccinated against it, the dog is likely to contract the virus.

Dogs that catch the flu are contagious for three weeks, and can cough for up to two months. Fortunately, it’s not as prevalent as it was three years ago when Chicago was the epicenter. Still, Dr. Natalie Marks, from the Blum Animal Hospital, says the days when dogs have a Fall to Spring flu season are gone.

“It can affect male or female, young and old, sick and healthy, dogs that are isolated or dogs that are communal any month of the year — it doesn’t discriminate,” she said.

The good news is that there are only two known strains. They have not mutated and the vaccine is highly effective.

The not-so good news is that Animal Welfare League in Chicago Ridge has been forced to temporarily shut down part of its facility because of a respiratory disease sweeping the shelter, which apparently affects dogs. The animal shelter is only offering limited services, and is not accepting stray or owner-surrendered dogs for the time being, according to a Facebook post.

Dog adoptions have also been halted.

The sign of the dog flu is a cough.

“If you’re dog is coughing … this would not be a dog that I would necessarily bring to a daycare setting or a dog park or a communal area where it could be spread,” Dr. Marks said.

She says those vaccinated dogs that catch the flu anyhow will suffer far less and recover more quickly.