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Canine Influenza in Dogs

The virus that causes dog flu, Influenza Type A (H3N8), was first identified in Florida in 2004. It primarily infects the respiratory system and is extremely contagious. A vaccine was granted full license by the United States Department of Agriculture in 2009 (Nobivac® Canine Flu H3N8). Some dogs can be exposed to the virus and fight off infection without showing clinical signs.

Symptoms and Types

Dogs that are infected with the canine influenza virus may develop two different syndromes: 

1. Mild – These dogs will have a cough that is typically moist and can have nasal discharge. Occasionally, it will be more of a dry cough. In most cases, the symptoms will last 10 to 30 days and usually will go away on its own. 
2. Severe – Generally, these dogs have a high fever (above 104 degrees Fahrenheit) and develop signs very quickly. Pneumonia, specifically hemorrhagic pneumonia, can develop. The influenza virus affects the capillaries in the lungs, so the dog may cough up blood and have trouble breathing if there is bleeding into the alveoli (air sacs). Patients may also be infected with bacterial pneumonia, which can further complicate the situation.

General signs of these syndromes include:

• coughing
• sneezing
• anorexia
• fever
• malaise

Red and/or runny eyes and runny nose may be seen in some dogs. In most cases, there is a history of contact with other dogs that carried the virus. 

Diagnosis

Besides a physical, the veterinarian will want to perform a complete blood count and clinical chemistry on the dog. Usually, increases are seen in the white blood cells, specifically the neutrophils, a white blood cell that is destructive to microorganisms. X-rays (radiographs) can be taken of the dog's lungs to characterize the type of pneumonia.  

Another diagnostic tool called a bronchoscope can be used to see the trachea and larger bronchi. Cell samples can also be collected by conducting a bronchial wash or a bronchoalveolar lavage. These samples will typically have large amounts of neutrophils and may contain bacteria. 

Detecting the virus itself is very difficult and is usually not recommended. There is a blood (serological) test that can support a canine influenza diagnosis. In most cases, a blood sample is taken after initial symptoms develop and then again two to three weeks later.