(CNN)Dozens of dogs in different parts of Norway have been hit by a deadly mystery disease in the past few weeks, and officials are scrambling to identify the cause.
The first cases were spotted in the capital city of Oslo, but dogs have since fallen sick all over the country -- cases were reported in 13 of Norway's 18 administrative regions.
Representatives from the Norwegian Food Safety Authority and Norwegian Veterinary Institute told CNN that at least 25 dogs had died so far.
Autopsies did provide a clue on Monday: two bacteria have been found in "abnormally large quantities" in multiple dogs that had died, according to the Norwegian Veterinary Institute.
However, there are no more concrete details at this stage. Some possible causes have been ruled out, like Salmonella, Campylobacter, or poison -- but the investigations have not yet provided any definitive answers, said the Food Safety Authority.
The symptoms are not completely new -- they have been seen before in sick dogs, but the sharp increase in cases is unusual, according to the Veterinary Institute. It said the illness is also more acute than before -- not only are the dogs getting sick, but once ill, they deteriorate quickly. One dog over the weekend was euthanized due to an "acute" progression of the disease, and another died before it could arrive at the clinic.
The Food Safety Authority, Veterinary Institute, and the Norwegian University of Life Sciences are working together on the investigation. They have sent a survey to pet owners to collect more information, as well as coordinating with clinics and 2,000 veterinarians across Norway, according to the Veterinary Institute.
The research teams are also continuing to conduct virological studies, autopsies, and laboratory analyses of the dead dogs to further narrow down the cause. Apart from bacteria, possible causes might include viruses, fungi, parasites, or even environmental causes like poor water quality, said the Veterinary Institute. The total number of affected dogs is not yet clear.
In the meantime, the authorities warn dog owners to keep their dogs on leashes and stay alert for symptoms. When dogs are walked, they should not have contact with dogs they meet on the road or in the park as long as the situation remains unclear, said Ann Margaret Grøndahl of the Food Safety Authority.
There is so far no suggestion that the illness is coming from dog food, or that the illness can spread to humans.