NEW YORK — (CNN)  As new cases of canine influenza spread across several states, veterinarians are urging vigilance after hundreds of dogs contracted the virus.

Last month, more than 1,000 pooches got dog flu in Chicago, while one in the Atlanta area and another one in Ohio tested positive this week.

Other positive results have been reported in various states, including Iowa, Indiana, Massachusetts and New York, according to Cornell University.

Here’s what you need to know about the virus:

What causes it?

Dog flu is caused by two viruses — A H3N8 and A H3N2 — which only affect animals, according to the Centers for Disease Control and Prevention.

Can humans get it?

No evidence has been found of transmission from dogs to people, experts say.

Is it safe to take my dog to the park?

Depends on where you live.

As a precaution, dog owners in states affected by the virus should avoid dog parks, grooming spots and other areas where pets gather. The virus can especially spread among dogs staying in kennels and shelters.

What strain is causing the U.S. outbreak?

The U.S. outbreak is as a result of a virus closely associated with the H3N2 strain, according to Cornell University. The revelation spurred concerns because the strain, which is mostly found in Asia, had not been detected in North America until last month.

How did the virus start?

The most recent one afflicting the U.S., the H3N2 strain, is an avian flu virus that’s different from its human counterpart. In addition to dogs, it affects cats, and was first reported in the United States last month. Before then, it was mostly limited to countries such as China and Thailand.

The second one, the H3N8 strain, originated in horses before it crossed over to dogs, and the first U.S. case of the virus in pups was reported in 2004.

“Scientists believe this virus jumped species (from horses to dogs) and has adapted to cause illness in dogs and spread among dogs, especially those housed in kennels and shelters,” the CDC says.

Is dog flu fatal?

Yes and no.

While a small percentage of dogs die, others can get severely sick when pneumonia sets in. Some dogs show no symptoms at all, the CDC says. In the latter cases, a veterinarian can conduct a test to detect the virus in dogs.

What are the symptoms?

Signs of dog flu are similar to humans’ flu. The animals cough, get a runny nose, are lethargic, lose appetite and have a fever. But some dogs don’t show any symptoms.

How is dog flu treated?

There’s no specific treatment because it’s a viral disease, but dogs can get supportive care to boost immunity. If a secondary bacterial infection is diagnosed, antibiotics can be prescribed. A vaccine is also available in the United States, but only for H3N8, the CDC says. It’s not known whether it can help prevent the newest strain — H3N2 — which is causing the latest outbreak.

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