Researchers have discovered why so many dogs in Norway became seriously ill and died in 2019

In the autumn of 2019, many dog owners in Norway were afraid. Across the country, dogs suddenly arrived with acute bloody diarrhoea, and several died. Veterinarians had no clear answers. What was happening?

Acute bloody diarrhoea in dogs can have several causes, and in many cases no clear explanation is found.

This time, however, one bacterium in particular – Providencia alcalifaciens – emerged as the prime suspect during the investigation.

The Norwegian Veterinary Institute, NMBU, and the Norwegian Food Safety Authority launched an extensive investigation into the outbreak.

Could the bacterium cause fatal intestinal damage?

The bacterium mentioned above was detected in a majority of the autopsied dogs and in faecal samples from sick dogs.

At that time, veterinarians knew little about what role it actually played in causing severe intestinal damage in dogs.

Back then, the conclusion was that Providencia alcalifaciens was highly likely to have had something to do with the illness.

Further research on the collected material was necessary to prove that the bacterium could indeed cause fatal intestinal damage in dogs.

New samples provide new answers

Researchers have made important new discoveries about this bacterium in a collaborative project between the Norwegian Veterinary Institute, NMBU’s Faculty of Veterinary Medicine, and others.

Veterinarians and animal clinics send the Norwegian Veterinary Institute samples from dogs with diarrhoea.

In the first years following the major outbreak, the institute found several cases of Providencia alcalifaciens in late summer and early autumn.

“It appeared more like isolated cases than an actual outbreak. After that, it seemed to fade away,” says Bjarne Bergsjø.

He is a veterinarian and head of the bacteriology lab at the Norwegian Veterinary Institute. All bacterial samples were preserved for future investigations.

An autumn disease

In this study, researchers examined bacterial isolates from dogs with diarrhoea collected over several years (2019, 2020, and 2021, as well as samples from 2005 and 2006).

About a quarter of the samples came from NMBU’s Faculty of Veterinary Medicine, and the remainder from the Norwegian Veterinary Institute.

“We found the bacterium only rarely outside the autumn season. This pointed towards a possible seasonal pattern. The finding strengthened our suspicion that the bacterium could have been an important contributing factor to the outbreak,” Bergsjø says.

At the same time, researchers observed that even when the bacterium was detected, illness did not always occur.

This prompted them to ask whether there might be something specific about the bacterial strain had triggered the outbreak.

Mapping the bacterium’s ‘family tree’

To understand what made P. alcalifaciens dangerous, the researchers examined samples collected in Norway. In total, 273 samples were studied, the vast majority of which were from Norwegian dogs.

These samples were compared with 48 P. alcalifaciens samples from other studies, including international sources.

The researchers used a type of analysis that 'reads' the entire DNA of the bacteria to see how they were related.

The analysis revealed a clear pattern. The bacteria clustered into two genetic groups: A and B. The most interesting findings lie within group A.

The investigations showed that bacteria from group A were overrepresented in samples from the sick dogs, including many from the 2019 outbreak.

Particularly aggressive types

When analysing subgroups within group A, the researchers found that some frequently carried extra genes associated with the ability to cause disease.

“Several subgroups stood out by having plasmids that resembled one another,” says researcher Eiril Moen Soltvedt at NMBU’s Faculty of Veterinary Medicine.

This long-term work forms part of her doctoral research.

She explains that plasmids are pieces of DNA that bacteria can exchange – essentially the bacteria’s downloadable toolbox. This ‘package’ of genes makes these variants particularly aggressive.

In other bacterial species, similar genes provide the bacterium with a type of syringe that injects proteins into intestinal cells, disrupting their normal function.

These injected proteins can give the bacteria the ability to break down the intestinal mucus layer and suppress the immune response.

In this study, researchers identified genes resembling those found in dangerous E. coli strains and a toxin gene from the plague bacterium Yersinia.

“We found that nearly all bacteria in subgroups A‑1 and A‑4 carried such ‘toolboxes’ with potential disease-causing genes. This suggests that these dangerous variants did not evolve slowly, but rather ‘downloaded’ the traits that make them harmful,” Soltvedt explains.

What does this mean for dog owners?

Simen Foyn Nørstebø, researcher at the Norwegian Veterinary Institute and co-author of the study, believes the findings have direct practical relevance.

“Now we know that there are specific variants of P. alcalifaciens that seem to appear each autumn in Norway and are particularly dangerous to dogs. This allows veterinarians to more easily identify the bacterium as the cause. In the long run, it means we might develop more targeted treatment and perhaps even prevent disease,” he says.

Researchers also found the bacterium in some healthy dogs.

This indicates that P. alcalifaciens does not always cause illness on its own, but takes advantage of situations where the dog is weakened. This could be due to stress, another illness, or damage to the intestine.

Previous advice still applies

Some soil samples collected near the Veterinary Hospital at NMBU in 2021 were almost identical to bacteria from sick dogs.

“Whether this is because the bacterium can survive in soil on its own or because the soil had been contaminated by faeces from sick dogs is still unclear,” says Nørstebø.

Regardless of the reason, the finding suggests that the environment may play a role in the chain of transmission.

He adds that the advice given during previous outbreaks still stands: keep dogs away from rotten food scraps, rubbish, faeces, and stagnant water, and contact a veterinarian if your dog develops bloody or severe diarrhoea with reduced general condition.

Most dogs that receive proper veterinary treatment for such symptoms recover.

Nørstebø believes that monitoring this bacterium may make us better prepared when the next autumn approaches.

Are some dogs more vulnerable?

The next step is to investigate whether the genes associated with disease are active in the dog’s intestine, and what role they play in disease development.

There is also a need to determine why some dogs are more vulnerable than others, and where the bacterium resides in nature between outbreaks.

“The answers to these questions will determine whether we can one day prevent disease outbreaks rather than merely respond to them,” says Nørstebø.

The same type of bacterium makes both animals and humans ill

The researchers also compared the Norwegian bacteria with samples from other parts of the world.

The comparison shows that the most dangerous variants belong to a distinct international lineage, but with a distinct Norwegian ‘branch’ that played a central role in the outbreak in this country.

“It's interesting to see that bacteria from dogs and humans ended up in the same genetic subgroups,” says Nørstebø.

Among other things, the researchers found a Norwegian dog bacterium that was very similar to a bacterium from a human with diarrhoea.

This may mean that the bacterium can jump between species, like several other bacteria that cause disease in both animals and humans, Nørstebø explains.

“In the 2019 outbreak, we did not detect any cases in which humans were infected by sick dogs. This suggests that several factors must align before such bacteria can infect people. Nevertheless, it's wise to maintain good hygiene when handling a dog with diarrhoea,” he says.

Reference:

Soltvedt et al. Canine Providencia alcalifaciens: virulence factors and phylogenetic analysis of an emerging enteropathogen, Microbial Genomics, 2026. DOI: 10.1099/mgen.0.001628

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Read the Norwegian version of this article on forskning.no

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