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Update on H3N2 Canine Influenza (Dog Flu) Virus

April 28, 2015 – Experts from CDC’s Influenza Division have analyzed genetic sequences of the H3N2 canine influenza A virus recently detected in the United States and found no evidence suggesting an increased potential for this virus to infect humans or cause severe disease in humans. Therefore, the risk to humans posed by this virus continues to be low and is equivalent to that associated with previously circulating H3N8 canine influenza viruses.

CDC conducts year-round surveillance and genetic analysis on circulating human and novel influenza A viruses in order to assess human health risk and prepare for vaccine virus selection. This work is based in part on an informal inventory of genetic mutations that are associated with viral characteristics like increased transmissibility or severity. While genetic analysis of the H3N2 canine flu virus did not show any of these markers, the agency will continue to analyze this virus and watch the field situation closely.

H3N2 canine flu virus is responsible for an outbreak of dog flu reported in the Chicago area according to a press release issued by Cornell University, home to the New York State Animal Diagnostic Laboratory. Dog flu is a contagious respiratory disease in dogs. Two canine influenza viruses have been identified worldwide: an influenza A H3N8 virus and an influenza A H3N2 virus. No human infections with either of these canine influenza viruses have ever been reported.

Previously, canine influenza A H3N8 viruses have been identified in U.S. dog populations. However, testing at the New York State Animal Diagnostic Laboratory and the Wisconsin Veterinary Diagnostic Laboratory showed that the dog flu virus responsible for the current outbreak in dogs is an H3N2 virus. This virus is similar to H3N2 dog flu viruses that have been detected in dogs in parts of Asia since 2007.

Updates on ongoing antigenic and phenotypic analyses will be shared when they are available. For more information on canine influenza (dog flu), please visit .

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