BY: Samantha Bartlett
Canine influenza is a type A influenza virus. There are two strains that have been identified in the United States. Both of these strains, H3N8 and H3N2, were believed to originate in a species other than the dog and jumped species where they were then transmitted from dog to dog. H3N8 was identified in Florida in the early 1990s. It is believed that the virus originated in racehorses and then mutated to affect racing greyhounds housed in proximity to the horses. H3N2 was first identified in Asia and was believed to have mutated from an avian influenza strain most likely found in market birds in China, South Korea and Thailand. H3N2 made its way to Chicago in 2015. Since then, the virus has jumped species again to infect shelter cats that were housed in proximity to infected dogs.
In 2017 another outbreak of H3N2 occurred that was believed to have originated from two dog shows in the southeast. From there the virus spread to Georgia, Florida, Tennessee, Kentucky, North and South Carolina, Louisian, Missouri and Illinois. To this point, there is no evidence that other species have been affected, including humans. A group at Cornell University’s Animal Health Diagnostic Center has published a map based on most recent surveillance data. Currently, the main areas for influenza cases appear to be California (209 cases in past 45 days) and Southern Ohio/Northern Kentucky (40 cases). This map can be accessed at https://ahdc.vet.cornell.edu/news/civchicago.cfm.
Diagnosis of canine influenza is difficult because dogs typically present with non-specific signs that may be associated with kennel cough. Most dogs have a cough that lasts for 10-12 days despite treatment. Other symptoms include lethargy, fever, vomiting or nasal or ocular discharge associated with secondary bacterial infections. More severely affected dogs may develop pneumonia. Diagnosis is made with virus isolation, antigen tests or PCR. These tests are costly in owner perspective and many owners may decline diagnostics. Cats exhibit upper respiratory signs. To date there have been no deaths associated with canine influenza in cats.
Strict biohazard protocols should be implemented since the virus is easily spread on fomites. People that have contact with infected pets should wash and disinfect hands and clothes before handling other dogs or cats. In addition, all surfaces and equipment should be disinfected thoroughly between pets. The virus can remain viable on surfaces for up to 48 hours. The virus is easily killed with most commonly used kennel disinfectants.
Most dogs exhibit mild respiratory signs and cough and recover without incident. However, a few deaths have been reported. Treatment is largely supportive until the virus runs its course. It is recommended that affected dogs and any dogs in the household remain isolated for 4 weeks after diagnosis. Vaccines exist for both strains of Canine Influenza and a bivalent vaccine covering both strains is also available. Vaccination may not entirely prevent the flu, but will reduce the severity of symptoms if the dog does get sick. The vaccine is considered a lifestyle vaccine and is given on a case-by-case basis. Dogs that interact with many other dogs and travel frequently are good candidates for vaccination. There are no approved influenza vaccines for cats.