Canine influenza: Veterinary resources

Signs of canine influenza in dogs

Virtually all dogs exposed to canine influenza virus become infected, with approximately 80% developing clinical signs of disease. Approximately 20% of infected dogs have no signs at all.

The most common sign is a cough that persists for 10 to 21 days. This cough may be soft and moist or it may be dry, similar to the cough characteristic of canine infectious respiratory disease complex ("kennel cough”). Other signs include the following:

• Thick nasal discharge
• Fever (often 104-105^oF)
• Lethargy
• Ocular discharge
• Reduced appetite

Complications such as secondary bacterial infection can develop in 10-20% of infected dogs, causing more severe illness and pneumonia. The overall case fatality rate is considered low at 1-5%.

The H3N8 virus has an incubation period of one to five days, with clinical signs in most cases appearing two to three days after initial exposure. Dogs infected with the H3N2 virus may start showing respiratory signs between two and eight days after infection. Infections are most contagious during the incubation period.

Signs of canine influenza in cats

Cats infected with H3N2 may display signs of upper respiratory infection, including sneezing, nasal discharge, and congestion, as well as malaise, lip smacking, and excessive salivation or drooling.

Canine influenza is transmitted through respiratory droplets or aerosols. This means that canine influenza virus can travel from infected dogs to uninfected dogs through the following:

• Direct contact, as through licking or touching nose-to-nose
• Coughing, barking, and sneezing
• Contaminated objects like food and water bowls, toys, kennel surfaces, collars, or leashes
• Skin and clothing of people who have been in contact with infected dogs

Settings where dogs are exposed to other dogs, such as animal shelters, boarding facilities, dog daycares, dog parks, and dog shows or competitions, increase the risk of canine influenza, particularly when an outbreak is occurring in the area.

Infected dogs can be contagious even if they seem healthy and can spread the virus for up to four weeks after they were first exposed to it. The virus can remain viable on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours, but is easily killed by common disinfectants. Rigorous biosecurity and disinfection practices can reduce the risk of disease transmission.

Because the signs of canine influenza are similar to those of other infectious respiratory illnesses in dogs, a diagnosis of canine influenza requires certain tests. Options include the following:

• Polymerase chain reaction (PCR) testing for virus nucleic acid
• Serologic testing for antibodies against the virus
• Virus isolation
• Immunoassays to detect virus antigen

Serologic testing is considered the most reliable way to confirm canine influenza virus infection. However, an accurate test requires two serum samples: the first collected when the patient first presents and the second two to three weeks later. Because of these time constraints, PCR testing is considered by many to be the preferred test for diagnosing infection in the acute stage. To minimize the chance of a false-negative PCR result, it is recommended that samples (usually deep nasal swabs) for PCR testing be collected within four days after onset of clinical signs. Some PCR tests also detect other influenza viruses, which can be useful for ruling out other causes of infection. Contact your diagnostic lab for their recommendations on testing and sample collection.

No specific treatment exists for canine influenza. Most cases are mild and self-limiting, with dogs recovering within two to three weeks. For dogs with more severe illness, supportive care is recommended, and may include the following:

• Fluids to manage dehydration
• Nutritional supplementation
• Antimicrobials to combat secondary bacterial infections/pneumonia
• Nebulization with saline solution and/or coupage to help loosen lower airway secretions
• Nonsteroidal anti-inflammatory medications as needed to reduce fever and inflammation

Note that antiviral drugs such as oseltamivir that used in humans with influenza A are neither approved nor recommended for dogs or cats with canine influenza.

To prevent transmission of the virus, dogs with H3N2 canine influenza need to be isolated for at least 21 days and dogs with H3N8 canine influenza for at least seven days.

Implement biosecurity and isolation protocols

An isolation period of four weeks from onset of illness is recommended for dogs with suspected or confirmed canine influenza, and for dogs with known exposure to the virus.

• Keep known or potentially infected dogs at least 20 feet away from other dogs and cats.
• Have the dogs enter and exit the hospital through a door other than the main door, and take them to a room where they won’t be exposed to other animals—preferably one with a separate air supply.
• Wear personal protective equipment (e.g., gowns, booties, and disposable gloves) when examining or caring for the dogs.
• Thoroughly clean and disinfect areas where potentially infected dogs are examined and treated, as well as all instruments used.
• Refrain from hospitalizing dogs with non-critical health concerns to prevent other patients (including cats) from becoming exposed.
• Practice hand hygiene.

Consider whether vaccination is warranted

Vaccines are available for both H3N8 and H3N2 canine influenza. A bivalent vaccine offering protection against both strains is also available—and might be preferred as it may provide broader immunity. Although these vaccines will not necessarily prevent infection, they can substantially reduce severity and duration of illness, as well as viral shedding. No canine influenza vaccines have been approved for use in cats.

The risk of the dog becoming exposed to the virus is important when determining whether to vaccinate. Currently, routine use of canine influenza vaccines is not recommended. However, vaccination may be advisable in areas where the virus is known to be circulating, particularly for dogs that are boarded or otherwise exposed to other dogs through activities or places where dogs congregate. Dogs that travel may also benefit from vaccination.

Initial vaccination can begin as early as six weeks of age. The recommended protocol is two doses two to four weeks apart, with revaccination within one year after the second dose. Subsequent boosters are given annually. A single vaccination is unlikely to be protective in high-risk settings.

Educate owners

Owners whose dogs are coughing or exhibiting other signs of infectious respiratory disease have an important role to play in preventing others from becoming ill. Advise them to keep their dog away from other dogs while their dog is sick (if canine influenza is not suspected) or for four weeks after their dog first became ill (if canine influenza is suspected).