Canine Influenza (Flu)

What is canine influenza (flu)?

Canine influenza is a highly contagious viral respiratory disease that can spread among dogs in close contact with one another through coughs and sneezes and contaminated objects like water bowls. Indoor housing facilitates transmission. Although the virus can be spread between dogs by people on infected skin or clothing, there are no instances of dog influenza viruses being transmitted to humans.  Settings in which dogs are in close proximity to one another, such as day care centers and shelters pose increased risks for spread of canine influenza and other respiratory viruses. Dogs visiting dog parks and participating in outdoor events with other dogs might also be at risk for infection, but the risk of outdoor transmission is much lower than for indoor transmission.

The type of influenza virus causing outbreaks in dogs in the United States (H3N2) spreads following importations of infected dogs from China and Korea; each outbreak then burns itself out until another infected dog is imported. This is not the same as the influenza virus causing disease in poultry, dairy cattle, humans, cats, and other wildlife species in the United States (H5N1 clade 2.3.4.4b), which has not yet been associated with significant disease in dogs. Previously, another type of influenza virus caused disease in dogs (H3N8). This virus was predominantly responsible for disease in shelters and now is considered extinct.

Canine influenza can affect dogs of any age, breed, and sex, and infections can occur year-round.

What are the clinical signs of canine influenza?

The clinical signs of canine influenza range in severity. Some dogs show no signs, but the majority develop a mild infection characterized by a cough lasting 1-3 weeks. Other possible signs include sneezing, ocular and nasal discharge, fever, lethargy, and reduced appetite. In severe cases dogs may develop secondary bacterial infections that result in high fever and pneumonia. 

How is canine influenza diagnosed?

Canine influenza can be diagnosed in dogs by different methods, depending on how long they have been ill. Your veterinarian will consider your dog’s history and activities, such as spending time at a boarding facility, and whether the virus is known to be circulating in the area at the time. A variety of other infectious agents can cause similar respiratory signs, so laboratory testing is required to prove that an influenza virus is involved.

PCR testing can identify viral genetic material on swabs from the nose or throat but is often negative within a few days after onset of signs. Serologic testing, which detects the presence of viral antibodies in blood samples, can also be used, but can be positive in dogs that have been vaccinated for influenza or dogs that have recovered without developing illness. Because of the limitations of these tests, they are often only performed if an outbreak is suspected. Chest x-rays may be performed in cases with secondary bacterial pneumonia.

How is canine influenza treated?

Canine influenza is primarily treated through supportive care. Antibiotics do not affect the canine influenza virus but can be used to fight secondary bacterial infection. Antiviral therapy is not recommended for affected dogs. Dogs with contagious respiratory disease (of any cause) must be isolated from other dogs, usually for about a month, to prevent the spread of the disease.

What is the prognosis for dogs infected with canine influenza?

The prognosis for dogs infected with canine influenza is generally good. Most recover within two to three weeks. About twenty percent of infected dogs display no signs but may still be contagious. Severe cases, especially those involving secondary infections, are rare but can be serious. The mortality rate is low, between 1-5%.

How can canine influenza be prevented?

Canine influenza can be prevented through appropriate hygiene and disease control measures.  Vaccines against canine influenza H3N2 are available, but are generally only recommended in particular cases, such as for dogs that travel frequently or spend a lot of time in environments with other dogs like day care centers and dog parks. Talk to your veterinarian to determine if your dog should be vaccinated for canine influenza. Vaccines for H3N8 do not provide protection against H3N2 and vice versa.

Canine influenza virus can survive for up to two days in the environment but can be killed by common disinfectants. Keep your dog away from other dogs if they are coughing or sneezing and avoid interactions with other dogs that are exhibiting respiratory signs. Keep an eye out for alerts about canine influenza circulating in your area and minimize your dog’s contact with unknown dogs. Wash your hands after handling pets and avoid sharing dog bowls, toys, etc. with dogs outside of your household. Canine facilities can prevent the spread of canine influenza by maintaining regular infection control practices, proper hygiene, and isolation precautions. 

For more information

Canine Influenza PCR Test Developed at UC Davis

About Dog Flu, Centers for Disease Control and Prevention (CDC)

Canine Influenza, American Veterinary Medical Association (AVMA)