Everyone should know by now that there is an equine influenza virus, H3N8 2003 that adapted to the dog and this virus, H3N8 (CIV), is readily transmitted from dog to dog.  There are two vaccines available, one from Merck Animal Health (Intervet/Schering Plough) and one from Pfizer Animal Health.  However, what you probably didn’t know is that there is another influenza virus of avian origin, H3N2, which has adapted to dogs in Korea and China.  H3N2 is also readily transmitted from dog to dog, causing a similar disease to the H3N8 CIV.  The H3N2 has not, to date, been reported in the US, and H3N8 has not been reported in Korea or China.  There are several other influenza viruses that have been infecting dogs and cats since at least the 1940’s, but most are of human origin and they don’t spread among dogs or cats.

During the past two years, the swine origin H1N1 infected people and people infected their dogs and cats.  The H1N1 infection in dogs did not cause disease, but infection in cats with H1N1 did cause mild to moderate disease in some cats.  My laboratory technician and her 18-year-old diabetic cat was infected and both had clinical disease for several days.  It has just recently been reported that some dogs in Korea that were infected with H1N1 (and which were probably co-infected with H3N2) are now infected with a novel canine influenza virus, H3N1, which is likely a putative reassortment virus between the pandemic H1N1 2009 and H3N2 canine influenza viruses.  In contrast to the H3N2, which causes mild clinical disease in dogs, the H3N1 caused no clinical disease.  However, this is not uncommon, as many dogs that get infected with H3N8 also do not develop clinical disease.  As with many influenza viruses of all species, including those found in dogs and cats, secondary bacterial infections and multiple other factors (e.g. age and genetics) are often responsible for the severity of the disease.  An exception are the highly pathogenic influenza viruses like H5N1, which kills a high percentage of birds and humans that have been infected, as well as other species like the dog.  Fortunately, to date, none of the influenza viruses have adapted to the cat to cause an enzootic infection/disease.

Also of interest regarding viruses that infect humans and dogs is a recent report from the University of Helsinki’s Department of Food Hygiene and Environmental Health. They found human strains or norovirus (Hu Nov) in canine fecal samples from dogs living in households where either or both the dog or family members recently had experienced vomiting and/or diarrhea. Noroviruses are often referred to as the “Cruise Ship viruses” and are the leading cause of human gastroenteritis.

Ron Schultz, Professor and Chair, Department of Pathobiological Sciences