by ANDREW M. STREIBER, DVM
Q: With all the reports last year of a new strain of canine influenza infecting dogs across the United States, I’m wondering what symptoms I should be aware of in my dogs, and if humans are able to contract this particular strain?
A: The viruses of which you speak, known by two distinct proteins on their outer layer, are the H3N8 and H3N2 influenza viruses. They are distinguished from their human influenza virus counterparts by the fact that they are unique and distinct variants (or subtypes) of those known to human medicine.
The H3N8 virus was first discovered over forty years ago, while the H3N2 virus was elucidated more recently. Both viruses have origins in Asia: H3N2 in China and H3N8 in South Korea. Viruses are known for their ability to survive outside of their host for varying amounts of time, allowing them to travel. In the United States, the H3N2 subtype was first found in racehorses that had been racing at a specific track in Florida in the late 1990s. By 2004, it “jumped” to a colony of racing greyhound dogs, also racing at the same track. The virus, a disease of the upper respiratory tract, is spread intra-species via nose-to-nose contact, coughing, sneezing or contact with an inanimate object on which the disease may have settled. Once the greyhounds contracted the disease, H3N8 spread across the country, arriving in California around 2008. Fortunately, a vaccine already existed for that particular canine strain and dogs could be easily protected.
The H3N2 canine influenza virus (CIV) is a more recent, and a far more virulent (infectious) strain than the H3N8 virus. Like its predecessor, H3N2 is a variant (or subtype) virus, and causes an upper respiratory infection. The symptoms are similar – lethargy, inappetence, sneezing, coughing, nasal discharge, etc. — but the clinical disease this strain may cause can be worse than the H3N8, even, in rare instances, resulting in death. In the United States, H3N2 was first discovered in Illinois in April 2015. Also fast moving, H3N2 spread to California by the fall. Fortunately a vaccine exists for this strain as well, so dogs can be easily protected.
The bottom line for these strains of CIV is this: they are both influenza viruses, they present classic symptoms as a typical “flu” would, our canine population can be easily protected by being vaccinated, and to date no human has been diagnosed with a variant of either.
I hope this aids in your understanding of these diseases and helps put your mind at ease regarding the risk to you and your dogs.