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Canine Influenza – What We Know
History: The presence of an influenza virus capable of transmission from dog to dog was first identified in January 2004 in a population of racing greyhounds afflicted with respiratory disease at a racetrack in Florida. Eight of the 22 infected dogs died from pulmonary hemorrhage. An H3N8 influenza virus was subsequently identified as the cause.
More recently an outbreak of canine influenza has been reported primarily in the Chicago region. This time a different strain of influenza (H3N2) has been identified as the cause. It is believed this virus was introduced by dogs from Asia.
The virus: The influenza virus is an RNA virus belonging to the orthomyxovirus family. External antigens (responsible for the HA and NA classification) are specific to each particular subtype of the virus. The H3N2 influenza virus, unlike the H3N8 virus, can also cause respiratory illness in cats. Neither virus has been shown to be contagious to humans.
Shedding of the virus by an infected dog begins before clinical signs are noted and, on average, will last 5 days. The virus is spread by aerosol transmission of respiratory secretions via sneezing or coughing. Direct contact with respiratory secretions or contact with freshly contaminated surfaces will also serve as a source of exposure. The virus invades and kills the epithelial cells of the respiratory tract. Damage to the epithelial cells causes inflammation. The loss of ciliary function reduces the clearance of irritants, secretions, and secondary pathogens, further contributing to the signs of illness.
Clinical signs: Signs of infection typically develop within 2-5 days of virus exposure and are similar to those associated with a bad case of “kennel cough.” Lethargy, anorexia, nasal discharge, low-grade fever, and a persistent dry nonproductive cough are common clinical manifestations of the illness. The presence of secondary bacterial infections can exacerbate the severity of the illness. Severe pneumonia, pulmonary hemorrhage, and even death, though uncommon, may occur. Signs can persist for weeks.
Diagnosis: PCR testing specific for the H3N2 virus from nasal swabs performed early in the disease is presently the only method available to diagnose the new condition. Antibody testing is not yet available.
Treatment: Treatment is supportive in nature and should include antibiotics to control secondary bacterial infections.
Prevention: It is unknown whether the present influenza vaccine, which is specific for the H3N8 virus is effective against the H3N2 strain.
Avoidance of exposure to potentially infected dogs is the best means of prevention at the present time. This means avoiding dog shows or kennels where dogs from regions of active disease may also be present. To our knowledge, the virus has yet to be identified in the Minnesota area.
Appropriate environmental hygiene and the immediate quarantine of patients with respiratory signs are imperative to controlling the spread of infection. Most disinfectants will kill the virus. The virus can survive only for a short time on external surfaces.