While it was pretty well documented on the Worms & Germs Blog as it was underway, the full story regarding Ontario’s 2018 canine influenza outbreak(s) has now been published in the latest edition of Emerging Infectious Diseases. You can use the link above to access the full report, but here are some highlights.

• There were 104 confirmed cases. In most outbreaks, we talk about how that’s likely the minority of true cases. However, here, it probably accounts for the vast majority of cases, given the amount of contact tracing and testing that was performed.
• Transmission occurred in many ways, including while boarding, at a groomer, pack walking, day care, between neighbouring dogs and at a veterinary clinic.
• High attack rates were common. In an area where flu is not normally present, when it hits, large numbers of dogs can be affected quickly. Large clusters of disease, or situations where most or all dogs in a group develop respiratory disease around the same time, is a trigger for me to test for canine flu. That’s true even if there’s no initial link to imported dogs. One of our large clusters was first identified because of a high attack rate of respiratory disease in a good kennel. The link to imported dogs was only found later.
• Outbreaks were the result of multiple introductions of H3N2 canine influenza virus into Canada through dogs imported from Asia (China and South Korea).
• Two dogs died from complications of influenza. Both were older dogs, which isn’t surprising as older individuals are at greater risk of death from influenza, whether they’re dogs with canine flu or people with human flu. One other death was suspected but not confirmed.
• Some dogs shed the virus for a long period of time. We were able to collect serial samples from a reasonable number of dogs and some shed for at least 20 days, despite looking healthy after just a few days of illness.

The good news is that canine flu was eradicated. Good, old fashioned infection control was the key.  Some astute primary care veterinarians and responsible dog owners who were willing to quarantine infected dogs or facilities (e.g. kennels, groomers) for 28 days played a critical role.

While we were able to eradicate the virus in 2018, we’re under no illusion that it won’t come back. The large number of dogs imported from Asia and the lack of any quarantine or testing requirements for influenza means another outbreak is likely inevitable. However, we’ve shown that even with the introduction of a new virus to a population of dogs with no pre-existing immunity, it can be contained. It takes time, effort and money (and probably no small amount of luck), but it’s possible and worth the effort.

The map below shows the various clusters of H3N2 canine influenza identified in Ontario in 2018.