Canine Influenza - History, Symptons & Diagnosis

What is Canine Influenza?

Canine influenza is a highly contagious respiratory infection of dogs that is caused by an Influenza A subtype H3N8 virus.

Where did it come from and how long has it been around?

The exact origin is unknown, but it is thought to have mutated from a virus that causes equine influenza. While the first recognized outbreak is believed to have occurred in racing greyhounds in Florida in January of 2004, antibodies to the virus have been detected in stored serum samples from 1999-2003; no antibody has yet been detected in samples from prior to 1999.

Who is most at risk?

Because the virus is new to dogs, they have no natural immunity, meaning that all dogs exposed, regardless of age or breed, are susceptible to infection. Nearly all dogs that are exposed to the virus become infected, and approximately 80% will show clinical signs of disease.

How is it transmitted?

The virus is easily transmitted from dog to dog. The virus is spread by aerosolized respiratory secretions, contaminated inanimate objects, and humans moving between infected and uninfected dogs. Infected dogs may shed virus for 10 days from the onset of clinical signs. However, nearly 20% of infected dogs will not show any signs of illness and can become silent shedders and spreaders of the infection.

What is the incubation time?

The incubation period is 2 to 5 days after exposure before clinical signs may appear.

What are the signs and symptoms?

There are 2 general clinical forms – a milder syndrome and a more severe pneumonia syndrome. It is currently thought that about 80% of dogs with the disease will develop the milder illness, with signs including cough, low grade fever and nasal discharge. The most common clinical sign in the milder form is a cough that lasts for 10-21 days, despite treatment with antibiotics and cough suppressants. Most dogs have a soft moist cough, while others develop a dry hacking cough. Many dogs will have a thick nasal discharge which quickly resolves with appropriate antibiotic treatment.

A small percentage of dogs will develop a more severe illness with pneumonia and a high grade fever. Clinical signs of this syndrome include lethargy, weakness, rapid or shallow breathing, and a high fever between 105 and 107 F. This is likely to progress to pneumonia.

What other diseases can it look like?

The milder form looks very similar to kennel cough, especially when a dry hacking cough is seen. While both diseases are usually self-limiting, kennel cough usually resolves in 7-10 days, whereas canine influenza can take as long as 4 weeks to resolve.

How is it diagnosed?

Current diagnostic tests rely on detection of antibodies to the canine influenza virus, which can be detected as early as 7 days after the onset of symptoms. The preferred method is to obtain an acute sample during the first couple days of illness, and a convalescent sample 2 weeks later. This is to enable a comparison of titers to determine the presence of an active infection. If an acute sample was not obtained, the convalescent sample alone can determine if the dog had been infected at some point in the past.

When should you take your dog to the vet?

Keep a close watch on any dog that begins coughing, sneezing or exhibiting other signs. Contact your veterinarian if your dog develops a nasal discharge or fever (normal dog temperature is 100-102.5 F), or has a cough that persists. If the dog becomes depressed or stops eating and playing, the dog should be seen immediately.

Any dog showing signs of respiratory illness should be kept away from other dogs – including waiting outside the veterinary clinic until the dog can be immediately seen by the vet, to avoid exposing other pets to potential infection.