4 December 2013
It’s flu season so I’ll take advantage of the time to talk about flu of a different type… canine flu.
Canine flu is different from seasonal flu in people. It’s caused by canine influenza A H3N8, and has spread around the US is a rather meandering and unpredictable manner. It’s caused major problems in dogs in some areas, while other areas have been completely unscathed.
Influenza in animals is a concern for animal health, but there are also human health concerns because of the ability of many influenza viruses to cross species barriers.
The human health risk posed by canine flu has been unclear, but it’s been assumed to be low. One reason is that there have been no credible reports of disease in people working with infected dogs (although that’s a far-from-convincing degree of evidence). More importantly, from my standpoint, is that canine influenza originated from, and is still closely related to, equine influenza H3N8. This virus is widespread in horses internationally (and has been for a long time) and it’s not of much zoonotic concern.
However, it’s always good to have more information, and a recently published study (Krueger et al, Influenza and Other Respiratory Viruses 2013) explored this area further. The researchers looked at 304 people who were regularly exposed to dogs and 101 people who did not have canine exposure, and they looked for antibodies against H3N8 influenza in the subjects’ blood.
There were no differences in antibody levels between the two groups, suggesting no evidence of flu transmission from dogs to people.
The study would be more informative if they knew whether any of the people had been exposed to dogs with influenza (or respiratory disease, in general), so conclusions from the study are somewhat limited. The study targeted people at higher risk for exposure to dogs with flu, such as show dog owners, racing greyhound caretakers and similar groups, which is good. More useful would be a study looking at owners or caretakers of dogs with canine flu and comparing them to other dog owners and people with no dog contact (although that’s not easy to do).
So, we’re still left with some questions but no convincing evidence that canine flu is a human health risk. That being said, it would be better not to have it circulating in the dog population where a co-infection of an animal (or person) with H3N8 and a common human flu virus could result in a new virus that is more easily able to infect people and to which there’s little resistance in the human population. New flu viruses are potentially a big problem, as the bird/pig/human pandemic H1N1 flu virus showed a few years ago.