After a recent case of H3N2 influenza was detected in a dog in Calgary (that presumably originated in the US), there’s not much to update, which is hopefully good news. Things have been quiet. On one hand, that’s a bit surprising, because flu is highly transmissible and there’s basically no pre-existing immunity in the Canadian dog population (due to lack of exposure and low vaccination rates). On the other hand, it’s possible for new disease introductions like this to die quickly if the affected dog(s) have limited contact with other dogs.
Whether introduction of flu results in no additional cases, a small cluster of cases, or a large and sustained outbreak depends on the number and types of contact the infected dog has. The more dogs it encounters when it’s infectious, the greater the risk of spread. That’s infectious diseases 101.
Over the past two weeks, since we’ve been tracking this, there have been typical reports of respiratory disease in local dogs but no new cases of canine flu. We’re prepared to do testing, but haven’t heard about any high risk situations that would warrant more testing.
Does that mean this flu outbreak has been contained?
Maybe. At the individual dog level, canine flu looks no different than other causes of infectious respiratory disease in dogs. Most dogs with respiratory bugs get “flu-like” disease that resolves on its own. Some dogs get more severe disease and/or develop secondary pneumonia, and a small percentage of those dogs may develop fatal infections. So flu can’t be ruled out by looking at just a dog’s clinical signs, and we have to temper the current “no new cases” due to the typically limited testing of dogs with respiratory disease.
However, since flu is so transmissible, case patterns mean a lot. When flu spreads into the community, I expect to see noticeable outbreaks. Yes, the virus can circulate in household dogs and maybe be missed if people aren’t reporting disease, but I’d expect it to make it into kennels, day cares and/or shelters too. There, I’d expect to see high morbidity outbreaks with a lot of sick dogs in a very short period of time. We see outbreaks in these settings regularly, but with flu, I expect pretty much every exposed dog to get sick, usually around the same time. The pattern tends to be more dramatic with flu compared to other pathogens, and we haven’t seen that pattern so far following the Calgary case (but we’re ready to test if it does pop up).
At this point, it’s so far, so good. Each day that goes by without a new case or concerning situation is good news. I wouldn’t be confident saying the virus has been eliminated for at least a few more weeks, though. We still need a bit more time and testing for that.