ANIMAL TALES: What is Canine Influenza?

By Dana Carr, DVM 

What is Canine Influenza?

Influenza in dogs is caused by the canine influenza viruses (CIVs).  The two main CIVs in circulation internationally are H3N8 and H3N2.  Dogs are occasionally infected with human influenza viruses.  These viruses are highly contagious.  Currently there is no evidence to suggest that people can contract CIV.  The recent outbreak of the more severe H3N2 strain began in the Chicago area in March 2015.  It seems to be mostly contained to the Chicago area, but cases have been reported in neighboring Midwestern states.  Due to limited surveillance and reporting, the outbreak may be wider than reported.  The 2004 outbreak caused by the milder H3N8 strain has remained in circulation in the U.S. dog population.  We are seeing sporadic disease caused by H3N8 since then.  Unfortunately, the currently available influenza vaccines are not likely to be cross-protective against the H3N2 strain involved in the current outbreak.  Influenza viruses can change over time making them able to evade host defenses.  All previously unexposed dogs are susceptible to disease, regardless of age, sex, breed, or vaccination status.  However, the disease is more likely to become clinically significant in dogs housed in populations such as animal shelters, boarding facilities, and daycare settings.  

Clinical signs range from subclinical infection, or mild fever and lethargy, to severe and life-threatening pneumonia.  Most clinically affected dogs have signs that are typical of kennel cough, such as a mild cough in an otherwise active and normal dog.  Distinguishing CIV from other causes of acute respiratory disease (kennel cough) based on clinical signs is difficult to impossible.  The milder form requires minimal supportive care similar to any mild case of kennel cough (i.e. cough suppressants and isolation from other dogs).  Some dogs will go on to develop a more severe form of illness with high fever, loss of appetite, lethargy, nasal discharge, rapid breathing, and secondary pneumonia.  The severe form will require hospitalization and treatment is largely supportive.  Intravenous fluid support and coverage with broad-spectrum antibiotics are required.  Because this is an emerging disease, few dogs will have immunity to it.  Although vaccination does not prevent infection, it can reduce the severity and duration of disease, and should be considered in high risk dogs.  All dogs scheduled for boarding or other group events should be seen by their veterinarian at least 2 weeks prior to boarding to discuss recommended vaccinations and any necessary preventative measures.

Control of CIV relies on reducing the spread of virus between dogs by preventing individual animal exposure.  This is difficult as CIV is spread in part through aerosolized particles and droplets making it difficult to contain.  Also, some dogs may be subclinical and appear healthy while still shedding infectious organisms.  For dog owners living in known infected areas, minimize contact with other dogs.  Limit your exposure to dog parks, doggy daycare, grooming facilities, boarding facilities, training classes, and group gatherings.  Anytime your dog has respiratory signs (i.e. coughing, gagging, hacking, difficulty breathing) call your veterinarian beforehand so that we can take extra precautions to minimize contamination when you arrive.  If your dog has respiratory signs after traveling to an influenza endemic area, it is best to leave your dog in the car and have our veterinary team meet you at the car to triage the situation.

The bottom line:

• Keep your dog’s annual or biannual wellness visits to your veterinarian up-to-date. This gives us an opportunity to discuss lifestyle and risk factors and ensure your dog is vaccinated properly.
• If your dog is coughing do not ignore it and call your veterinarian.
• Do not allow your dog to socialize with coughing dogs.
• If your dog develops nasal discharge, lethargy, and a cough expect your veterinarian to perform chest radiographs and consider hospitalization.