Last week we talked about an outbreak of canine influenza that has been hitting the Chicago area hard in recent weeks. Some new information has come to light that puts an interesting spin on what’s been going on.


Previous outbreaks of influenza in dogs have been caused by the H3N8 strain of the virus. This is the disease that originated from a form of influenza that, in the past, had primarily infected horses. It appears that this outbreak of flu in dogs is different, however.


According to laboratory scientists at Cornell University and the University of Wisconsin:


The canine influenza outbreak afflicting more than 1,000 dogs in Chicago and other parts of the Midwest is caused by a different strain of the virus than was earlier assumed. Researchers at Cornell say results from additional testing indicate that the outbreak is being caused by a virus closely related to Asian strains of influenza A H3N2 viruses, currently in wide circulation in southern Chinese and South Korean dog populations since being identified in 2006. The H3N2 virus had not been previously detected in North America. The outbreak in Chicago suggests a recent introduction of the H3N2 virus from Asia.


H3N2 has caused infection and respiratory illness in cats. There is no evidence that it can be transmitted to humans.


This new information complicates matters. Some of the tests commonly used identify flu infections in dogs will not pick up the H3N2 virus, which makes me suspect that this outbreak is even bigger than it appears to be. (Cornell recommends testing be done using a “broadly targeted Influenza A matrix reverse transcriptase-polymerase chain reaction assay.”) Also, we simply don’t know if the canine flu vaccine that I recommended as a preventative measure in last week’s article will have any efficacy against this different form of the virus, which makes the advice to avoid areas where dogs congregate (kennels, doggy daycare providers, groomers, shows, dog parks, etc.) even more vital.


While the Chicago area has been at the epicenter of this outbreak, dogs in Wisconsin, Ohio, and Indiana have also been infected. If you live in the Midwest, protect your dogs by keeping them as isolated as possible and by washing your hands before petting them if you have had contact with dogs outside of your home.


And in case you’re wondering… this new (to the U.S. at least) form of canine influenza is not related to the highly pathogenic avian influenza epidemic that is leading to the deaths and culling of millions of birds in commercial and backyard poultry flocks across the Midwest (over 1.4 million turkeys have died in Minnesota alone, the last time I checked). That flu variant goes by the moniker H5N2 and was likely brought to the area by migrating waterfowl. H5N2 has sickened people in other countries, but no human illnesses have been reported as a result of this outbreak. Some H5N2 flu viruses do appear able to infect dogs and cats, so keeping pets away from bird flocks is probably a wise precaution at this time.



Dr. Jennifer Coates




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