(NewsNation) — Health officials in northern Michigan are investigating reports of an unidentified, 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.

A report from the Clare County Cleaver said more than 30 dogs in the area died in a matter of days from the virus.

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.

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. 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.

According to the American Veterinary Medical Association, canine parvovirus — or “parvo” —affects the gastrointestinal tracts of dogs and is spread by “direct dog-to-dog contact and contact with contaminated feces (stool), environments, or people.”

The virus is highly contagious, with unvaccinated dogs and puppies under 4 months at the highest risk.

According to the MDARD, canine parvovirus is not contagious to people or other animals. Also, it should not be confused with Parvovirus B19, which infects only humans.

The AVMA says there is no specific drug out there that will kill parvovirus in infected dogs.

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 of the mystery illness.

“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,” said Kim Dodd, director of the Michigan State University Diagnostic Laboratory. “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.”