“Seek and you shall find.”
That might be the simple explanation for why we’re hearing more about spillover of different types of flu viruses into dogs. Sporadic reports of dogs being infected by different flu viruses keep coming in these days, maybe we didn’t get this reports in the past because people just often didn’t bother testing dogs when doing surveillance of flu outbreaks in other species.
The latest incident is a report of finding antibodies against the H5N8 avian flu virus in a dog on a South Korean farm. This H5N8 strain is different from the H3N8 canine flu strain that has become a true "dog-flu", having adapted to dogs following spillover from horses.
This potentially emerging H5N8 avian flu virus has caused a lot of concern in southeast Asia as it can be devastating to poultry farms. It doesn’t sound like the dog in this case was sick, but the suspicion is that the dog was infected by eating infected poultry.
Avian flu viruses are a concern because some avian flu types can infect people and cause very serious disease. They can also cause devastating outbreaks in birds. Mixing of avian (and other) flu viruses with human viruses is the biggest concern, as it could potentially create a new pandemic virus that retains its high mortality in people but spreads much more easily like regular human flu strains. Adding more species to the mix adds more potential routes for transmission and flu virus recombination. It’s likely that dogs are of little to no concern here, and the dog was probably never infectious – it just got exposed, mounted an immune response and the virus died. However, it indicates the need to consider broader surveillance, involving various companion animal species, when investigation new influenza threats.