Dozens of dogs in Norway died this week of a mystery illness.

The Norwegian Food Safety Authority isn’t sure if the disease is contagious or just a series of individual cases, but acknowledged the situation is serious, The Associated Press reported.

Most of the cases have been in or around the capital city, Oslo, but the illness, whose symptoms include vomiting and bloody diarrhea, has also been reported in the cities of Bergen and Trondheim, and the northern Nordland municipality.

For now, authorities are advising dog owners to limit contact with other pets, according to Bloomberg News.

The Norwegian Veterinary Institute said autopsies detected two unspecified bacteria, but it’s not clear if that was the cause of the outbreak.