Canine Influenza by Frank Utchen, DVM

What is Canine Influenza?
Let's start with what an influenza virus is. Influenza viruses are a group of viruses. There are three types of influenza viruses: Type A (including the canine influenza virus), Type B, and the less closely related Type C. They produce fever, joint pain, and respiratory signs with which we are all familiar. Death is unusual but stems from respiratory complications and is most common in the very old and very young.

The virus has on its surface an assortment of proteins that determine its “strain” or subtype, and it is against these surface proteins that our bodies mount an immune response. If a viral strain mutates and sufficiently changes its surface proteins, a new strain is created. A new strain is one where the susceptible population (humans in the case of human influenza, dogs in the case of canine influenza) has no immunity and infection can spread rapidly.  Unless a mutation occurs as described, influenza virus strains will only infect one species of animal: Human influenza only infects humans; Equine influenza only infects horses; Canine influenza only infects dogs.

Molecular studies indicate that canine influenza represents a mutation from the equine influenza virus. Canine influenza was first confirmed in a racing greyhound in 2003 and has largely been a concern of the racing greyhound industry, particularly in Florida.

Starting in April 2005, the canine influenza virus has been seen in the pet populations of many states outside of Florida, from New York to Southern California.

What Happens to the Sick Dogs?
If a dog is exposed to the virus, there is a high likelihood it will become infected. However, although the infection rate is high, approximately 20% to 50% will simply make antibodies and clear the infection without any signs of illness at all.

The other 50% to 80% will get symptoms of the “flu:” They will have fevers, listlessness, coughing, and a thick nasal discharge. Most dogs will recover without complication, but a small percentage of dogs will actually get pneumonia. These are the dogs at risk of dying, and will require hospitalization, intravenous fluid therapy, and injectable antibiotics. Most of these dogs will recover provided they receive proper care. The death rate from canine influenza is believed to be less than 5%.

The majority of dogs that do become sick will recover in 2 to 4 weeks. Because this is an emerging disease, few dogs will have immunity to it and there is currently no vaccine. This means that any dog is a candidate for infection.

How Is The Disease Transmitted?
Dogs that are infected will shed virus in body secretions whether or not they appear to be sick. Virus transmission can occur from direct contact with an infected dog or with its secretions. Sneezing and coughing are the most likely routes by which it is spread. Kennel workers have been known to bring the virus home accidentally to their own pets. The virus persists on toys, bowls, collars, leashes etc.

How Are Sick Dogs Treated?
Pneumonia results from secondary bacterial infections (i.e., bacteria invade the lung after the virus has damaged the tissue and compromised its ability to defend itself). This can require high doses of intravenous antibiotics, as well as antibiotics delivered by “nebulization” (i.e., mixed into water and administered by a vaporizer by being inhaled). Many dogs with severe pneumonia will require intravenous fluids as well in order to stay hydrated.

One specific treatment for canine influenza may be the use of a medication called “Tamiflu”. This is an antiviral medication used in treating human influenza and is helpful if used early in the course of infection or in prevention of infection in exposed dogs. It prevents replication of the virus, and other studies suggest it impairs the development of bacterial pneumonia also.

Can Dogs Get Reinfected?
After a dog has recovered from canine influenza, immunity appears to last at least 2 years.

How Are Dogs Tested For Canine Influenza?
The most reliable test is a blood test for antibodies against the influenza virus. Blood samples are sent to the veterinary school at Cornell University.

Does Vaccination Against “Kennel Cough” (Bordetella) or Parainfluenza Offer Any Protection Against Canine Influenza?
No. These are all completely different infections; however, work on the development of a canine influenza vaccine is underway

Can People Get Infected?
People cannot get infected by this virus. Influenza viruses are specific for their host species and require a dramatic mutation in order to jump species. Don’t be concerned about getting an influenza infection from a dog, horse, or any other species other than humans.