Tell Me About: Dog Flu

Since it's been a long time since Toxicology Tuesday or Foreign Body Friday, I thought I'd start a series of veterinary posts about various pet diseases. I was inspired to write this post by the recent attention being given to dog flu, or more properly, Canine Influenza Virus (CIV.)

Background on influenza viruses: There are three basic classifications of influenza viruses. Class A viruses can affect many species of animals, including people. Class B and C affect humans only. While Class A viruses tend to be very species-specific (one virus affecting only one species), they are close enough in structure to each other that mutations can occur. This is the concern with swine flu and avian (bird) flu - that the virus may combine with human influenza viruses and be able to cross species lines, potentially creating a pandemic flu among people.

These viruses are named for the kinds of proteins that make up their structure. The proteins are called H and N for short, and there are many types of each protein. Thus, you get the dreaded H1N1 of swine flu, H5N1 in avian flu, H7N7 and H3N8 in equine flu. It is the H3N8 virus which is responsible for canine flu.

Let me reassure you right from the start - canine flu, unlike swine flu or avian flu, has no public health significance. To date, there are no reported cases of dog flu affecting people. You are not at risk from contracting influenza from your dog.

Canine Influenza Virus (CIV) is a newly reported disease. The virus is a variant of an old flu bug, the Equine Influenza Virus. It was first reported in the US in racing Greyhounds on tracks in Florida and New York in 2004. A similar disease outbreak occurred in foxhounds in the UK in 2002. In both cases, the dogs were being fed horse meat, and the supposition is that this is what lead to the virus mutating and "jumping" species from horses to dogs.

While the outbreak in Britain flared up and then fizzled, the US cases have been spreading. By 2005, 20 racetracks in 11 states were reporting 'flu in the Greyhound population. Since that time, the virus has moved out from the racetracks and spread to the pet dog population. At this time, 30 states, including Ohio, Kentucky and West Virginia, have reported CIV cases. Canine influenza is considered to be enzootic (a disease that is constantly present in an animal community but only occurs in a small number of cases) in five states: Florida, New York, New Jersey, Pennsylvania, and Colorado.

Because CIV is a new virus, all dogs are at risk. There is no natural immunity, and routine vaccinations to this point have not included canine influenza. One hundred percent of dogs exposed to CIV will become infected. About 20% will not show any clinical signs, and yet they will be shedding the virus (contagious) and exposing other dogs they meet. Only dogs are affected - not cats or other pets.

Of the 80% of dogs with clinical signs of CIV, the majority will have simple upper respiratory symptoms, like any other Canine Infectious Respiratory Disease (CIRD), commonly called "kennel cough." The disease starts 3 to 5 days after exposure with sneezing and nasal discharge. Lethargy and a fever may be present. About 7 to 10 days after exposure, the dog begins coughing. The cough is soft, not the honking, croup-like cough of Bordetella (bacterial cause of CIRD), but otherwise CIV is virtually impossible to distinguish from traditional "kennel cough" based only on clinical signs.

Approximately 10% of dogs that contract CIV may develop a more severe, potentially fatal, form of the disease, which manifests as pneumonia. Greyhounds in particular seem to be prone to a peracute (rapid onset) hemorrhagic pneumonia.

Canine Influenza Virus is highly contagious. It spreads from dog to dog via direct contact at dog parks, doggy day care facilities, and pet stores that encourage dogs to visit. Like the common cold, the virus is airborne, so coughing and sneezing dogs will spread the virus at boarding kennels, grooming parlors, in veterinary clinics, and over the back fence. It will also be possible to transmit the virus from dog to dog via contaminated surfaces such as shared food and water bowls, toys, and floors - even on your hands and clothes - since the virus can survive up to 12 hours on surfaces, up to 5 hours on your clothing.

The good news is, CIV is very susceptible to all common disinfectants and good hand washing techniques. The bad news is that most dogs which are actively shedding the virus are not clinical. Let me rephrase: The coughing dog who looks sick is not shedding live virus. The virus is shed primarily by dogs in the early stages of the disease, with mild sneezing only, or in the 20% of infected dogs who show no signs at all.

As responsible pet owners, we avoid taking our sick dogs out in public or exposing our dogs to dogs who look sick. Operators of boarding kennels, day cares, etc., refuse entry to dogs who are coughing. Veterinarians take special precautions when handling dogs with outward signs of contagious disease. BUT, no one is going to be able to predict which apparently healthy dog is infected with CIV. This means your dog may come home from a boarding kennel and develop CIV. Don't blame the kennel operator; it is likely that the infectious dog wasn't showing signs when it was admitted.

Treatment is supportive, just like when you have a cold - rest, fluids, maybe something to alleviate the symptoms. The majority of affected dogs recover within two weeks. In some cases, the cough may last 30 days. Severely ill dogs may need hospitalization with IV fluids, oxygen, and nebulization. This will require specialized isolation areas to prevent the spread of the disease to other dogs, and not all veterinary offices will be able to provide this service.

A new vaccine by Intervet/Schering-Plough was released in May with a conditional license from the USDA's Animal and Plant Health Inspection Service. It is given to dogs and puppies over 6 weeks of age, in a series of two injections two to four weeks apart. While the vaccine won't prevent the disease, it will lessen the severity and duration of symptoms, and will reduce the amount of virus shed and the length of time the dog is contagious.

Please talk to your veterinarian about the CIV vaccine and your dog's risk factors.

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I hope you enjoyed this post on canine influenza. If you would like to see more "Tell Me About" posts, please comment here on the blog or on my Facebook page and let me know what topics you would be interested in. Remember, I am a "dog and cat" vet. While I have some basic knowledge of other pets with hair, I have a strict "No feathers, no scales" policy.