It all started earlier this month. Veterinarians in Oslo, Norway were reportedly flummoxed by a rising number of sick dogs being brought to their practices. The pets appeared to be suffering from some sort of mysterious bowel disease, with similar signs of vomiting and bloody diarrhoea.

What had started in the capital city soon spread to most other regions of the country, sickening as many as 200 dogs, according to Norway's Veterinary Institute. By late Tuesday, the estimated death toll had risen to 26. On Wednesday, five new cases were added to the list.

The news has so frightened dog owners in Norway, visitors crashed the Norwegian Kennel Club's website in a flurry for information.

Even the experts are worried and baffled, searching desperately for answers. The emergency and safety director of the Veterinary Institute Jorun Jarp told local media it was "naturally alarming to have healthy Norwegian dogs dying so quickly."

"This is a very special situation," he said, according to a translation from The Guardian. "I haven't been in involved in anything like it before."

No one knows what the heck is going on, or even if these deaths are all connected. Post-mortem examinations have uncovered nothing sinister, and rat poison, Campylobacter and Salmonella have all been ruled out.

So far, there are only two types of bacteria that have been found in these dogs at unusual levels, and while these strains are sometimes responsible for diarrhoea in humans, it's currently unclear whether they're to blame for the recent outbreak.

To cover all possibilities, Norway's Food Safety Authority is also investigating mushrooms, viruses, other bacteria and parasites.

But while the symptoms between canines are remarkably similar, without some sort of distinct biomarker to go by, officials just can't be sure the dogs are even suffering from the same thing.

Food safety authority spokesman Ole-Herman Tronerud told a national Norwegian broadcaster that the illness seemed "very serious for a dog. But we don't know yet whether this is contagious or just a series of individual cases".

As long as the situation is unclear, officials suggest dog owners avoid close contact with other dogs, walking their dogs with a leash and avoiding dog shows. There are currently no signs this mysterious disease can spread to humans.