The recent H3N2 canine flu outbreak centred around dog shows in Florida has led to the usual round of questions and concerns.

How many dogs have been affected?

  • 3 dogs at parkHard to say. Cases aren’t carefully tracked and it is reasonable to assume that the majority of dogs that developed influenza (especially mild disease) were never diagnosed. Testing costs money and often doesn’t change how a dog with respiratory disease is managed, especially in the midst of an outbreak where influenza is assumed to be the cause. Therefore, a lot of cases get presumptively diagnosed but not confirmed. We keep working on ways to better track diseases like this but getting uptake is a challenge.

Is this a sign of a new problem?

  • No. Canine flu has been around for a while, although H3N2 canine flu is a relatively new arrival to the US. The virus causes sporadic larger-scale problems (like this outbreak), but then tends to retreat back to being a low-level disease. Outbreaks are always possible with a flu virus when it gets into a dog population with lots of close contact and limited immunity (not previously exposed or not vaccinated). A dog show is a great mixing vessel for viruses like influenza. All it takes is one infectious dog to cause an outbreak that can spread rapidly, as opposed to an infected household dog that has far fewer opportunities to infect other dogs during the relatively short infectious period.

Should my dog be vaccinated?

  • There’s rarely a yes/no answer to this question. Vaccination decisions should be based on a risk assessment, considering the likelihood that your dog will be exposed and the implications of infection. Things that increase the risk/need would include:
  1. Known presence of circulating canine flu in the area.
  2. Planned travel to an area where canine flu is present.
  3. Regular or upcoming interaction with lots of different dogs.
  4. Regular or upcoming interaction with dogs from areas where canine flu may be present.
  5. Dogs that are at increased risk of complications following infection.
  • This last factor is something I think is often overlooked (and we don’t have a lot of data to go on). Influenza infection is usually relatively benign, but it can be serious. In humans, we know that certain groups are at increased risk of complications. The same presumably applies to dogs, although it’s less well defined. For me, I get concerned about dogs with underlying heart and respiratory tract disease that might not tolerate infection well. I’m also concerned about elderly dogs and dogs with diseases that compromise their immune systems. These are groups of dogs that probably also have fairly low vaccination coverage rates in general.

What should I do if I live in an area where canine flu is present?

  • Know what’s happening, as much as you can. If an outbreak is largely confined to show dogs, average pet dogs are at lower risk, but show dogs may still interact with pet dogs at parks and other areas. If there are anecdotal reports of dogs getting sick from parks or other routine contacts, that’s useful to know (even though you have to take those types of reports with a grain of salt).
  • If there is known flu activity in the area (or vague reports of coughing dogs without a diagnosis), consider keeping you dog away from other dogs for a while. Influenza usually burns through a population fairly quickly, so we’re talking about days rather than weeks, in most situations. The less dog-dog contact, the less risk of flu spreading. To maintain an outbreak, the average dog with flu must encounter and infect another susceptible dog during the fairly short time it is shedding the virus.
  • If your dog develops signs consistent with influenza (e.g. cough, runny nose and eyes, lethargy, decreased appetite), keep it at home and away from other dogs. If you need to take it to the vet, call ahead so they can make a plan to prevent exposure of other dogs (e.g. examine your pet outside, bring it right into an exam room or isolation to prevent it from mixing with other patients).
  • Talk to your vet about vaccination.

What should I do if I live in an area where canine flu is not present?

  • Pretty much the same list as above. “Not present” really means “Not present at the moment” or “Not known to be present,” since any dog you pass on the street could potentially be infected. The risks are obviously much lower in areas where flu activity hasn’t been reported, but disease reporting in dogs is pretty lax.

Can cats be infected?

  • Yes, although it’s much rarer in cats than dogs.

Is there a risk to people?

  • I should say there’s “no risk” since that makes my life easier, but the answer is probably more accurately “there’s virtually no risk.” Infectious diseases like to do odd things ,and while there’s no evidence that H3N2 is a zoonotic disease concern, I can’t say with complete confidence that there’s not a rare subset of people who would be susceptible (usually with mild infection). Most likely, lots of people have been exposed and some have had the virus enter their bodies, where their immune system took care of it with no problems. Rare mild disease may not be occurring or may easily be overlooked. The bigger concern is the potential for a dog or other species to be infected with H3N2 and another flu virus at the same time, creating a new virus that could be more virulent in people. This is always a concern, but the odds of this happening are very low. The fact that it’s past peak human flu season probably helps too, reducing the odds of a co-infection.