Health officials in Norway are investigating after more than 20 dogs have died of a mysterious illness that appeared in the Scandanavian country.

"To have healthy and great Norwegian dogs die so quickly is naturally serious.  It's a very special situation I haven't been involved in before," said Jorun Jarp, emergency and safety director for the Norwegian Veterinary Institute.

Most of the cases are reported in and around Norway's capital Oslo, but others were in cities like Bergen and Trondheim, and even in the northern Nordland municipality.  The poor doggos could seem fine in the morning, but rapidly decline by the afternoon with symptoms including bloody diarrhea.  That has proven way too fast for owners to get their pets to the veterinarian in time, even if the vet knew what to do.

The disease doesn't seem to discriminate between breeds or ages.

"It is difficult because there are no obvious common features and no clear lab answers," said Dr. Hanna Jorgensen, also of the national Veterinary Institute.  "We do not have any conclusions to give yet.  But it is important to emphasise that many dogs recover from the disease."

The Norwegian Food Safety Authority is also involved in the investigation, given the potential for viral, bacterial, fungal, and/or parasitic causes.