(NewsNation) — Health officials in northern Michigan are investigating reports of a parvovirus-like illness being reported in dogs.

The unidentified illness, which has killed dozens of dogs, first appeared in Otsego and Clare counties, according to NewsNation local affiliate WOOD-TV. At least 30 dogs have died in Ostego, Melissa Fitzgerald, director of the Ostego Animal Control, said.

A report from the Clare County Cleaver said more than 30 dogs in that county died in a matter of days from the illness as well.

On Facebook, the Otsego Animal Shelter said dogs they’ve seen have parvo-like symptoms, such as bloody diarrhea, vomiting, lethargy and loss of appetite. However, when the canines are taken to a veterinarian, their parvo test comes back negative.

The illness is not affecting certain breeds more than others, Otsego Animal Shelter noted, and cases have been reported in counties around northern and central Michigan.

First clues indicate that it could be a new strain of the parvovirus. Canine parvovirus is a highly contagious viral disease that causes acute gastrointestinal illness in dogs, according to the Baker Institue for Animal Health. Although it most often affects puppies between six and 20 weeks old, elderly animals are also sometimes affected.

One older man who spoke to Fitzgerald said he lost a dog that was 12-14 years old from the illness, she said.

“His dog was the only thing he had left,” Fitzgerald said. “No family, no friends, that type of deal. He’s kind of secluded where he’s at, and it was sad.”

The Michigan Department of Agriculture and Rural Development is working with local animal control shelters, veterinarians, the Michigan State University Veterinary Diagnostic Laboratory and others to learn more about the reports and try to find a cause for the recent deaths.

While some of the first samples submitted to the Veterinary Diagnostic Laboratory were positive for parvovirus, additional diagnostic testing is ongoing, a news release said.

Because parvovirus is not a reportable disease in Michigan and is not uncommon in unvaccinated dogs, officials don’t have a clear picture of how many dogs in total have been affected in this particular cluster of cases, Courtney Chapin, communications manager for the laboratory, told NewsNation.

“Our team at the MSU VDL has the expertise to lead this diagnostic investigation, including the detection and identification of potential infectious or toxic causes,” Kim Dodd, director of the Michigan State University Diagnostic Laboratory, said. “Our work starts with looking for known causes of disease, and if none is found, we’ll explore novel explanations such as new virus variants. Our team is working hard to find clear answers, and we will provide an update when we know more.”

In a news release from the Michigan Department of Agriculture and Rural Development, the agency urged dog owners to work with their veterinarians to ensure their pet is up to date on routine vaccinations. Ostego County Animal Control said it hasn’t seen any dogs die that were properly vaccinated.

Health officials also say dogs and puppies should be kept away from other animals until they are fully vaccinated, or if the canines are showing any signs of illness.

“When you’re taking your dog for a walk, maybe don’t go pet everybody’s pet at this point,” Dr. Erin Schroeder, of the show Heartland Docs, DVM on National Geographic, said. “Because you don’t want to be a vector, you don’t want to be an inadvertent contaminant.”