Canine influenza (or dog flu) is an influenza A virus that infects dogs. There are two different dog flu viruses: H3N8 and H3N2 virus. Most dogs have no immunity to either strain of virus and it is highly contagious. It can also infect cats. It is not known to infect humans. The first documented case of H3N2 in Canada was on January 2, 2018 in Windsor-Essex County.