An unidentified virus has been sickening and killing dozens of dogs in northern Michigan over the past month.

Similar to canine parvovirus in symptoms, the illness first appeared in Otsego County in northern Michigan, but has spread further north, animal experts in the state say.

Parvo is a highly contagious viral disease of dogs that causes acute gastrointestinal illness in puppies, according to the Baker Institute for Animal Health. The disease, often fatal, most often strikes in pups between 6 and 20 weeks old, but older animals are sometimes also affected.

“The state is in a panic right now,” Clare County Animal Control Director Rudi Hicks told the Clare County Cleaver.

The new unidentified virus is suspected to have come from Louisiana . It kills dogs within days of symptoms, Hicks told the outlet.

How many dogs died? What symptoms did they have?

More than 30 dogs had died of the disease in Clare County alone as of Thursday, Hicks said. It’s not yet known how the virus spreads.

“It is a virus much like parvo, possibly a different strain” said Melissa FitzGerald, director of Otsego County Animal Shelter in Gaylord, Michigan, about 50 miles south of Mackinaw City.

Symptoms, she said, include bloody diarrhea, vomiting and lethargy.

What dogs are affected by the virus?

The virus affects puppies and older dogs, and when the animals are tested by veterinarians, the initial test for parvo is negative, FitzGerald told USA TODAY.

Usually, the dogs die within three to five days. 

As of Monday, FitzGerald said, no dogs at the Otsego County shelter, 70 miles north of Clare County, had contracted the virus.