Canine influenza or og flu refers to varieties of Influenzavirus A that create influenza in canines. The most important of these is the equine influenza virus H3N8, which in 2004 was discovered to cause disease in dogs. Because of the lack of previous exposure to this virus, dogs have no natural immunity to this virus. Therefore, transmission rates from dog to dog are very high. Canine influenza is either approaching or is currently endemic in the dog population in the United States. It is a disease with a high morbidity but a low mortality.