Canine Influenza

What is canine influenza?

Canine influenza, also known as dog flu, is a highly contagious respiratory disease caused by a specific Type A influenza virus. These types of viruses are known to infect dogs as well as cats, but have never been reported to infect humans.

There are two different influenza A dog flu viruses. They are identified based on the composition of two proteins in the outer layer of the virus capsule, which are hemagglutinin (HA) and neuraminidase (NA). At the present time, two strains of canine influenza have been identified in the United States: H3N8 and H3N2.

Where did canine influenza viruses come from?

Canine H3N8 influenza was first identified in Florida in 2004 in racing Greyhounds. It is thought this strain developed from an equine strain that jumped from horses to dogs. Since being detected in 2004, canine H3N8 influenza has been diagnosed in dogs across the United States.

Canine H3N2 was first seen in the United States in March 2015 following an outbreak of respiratory illness in dogs in the Chicago area. Prior to this, reports of canine H3N2 influenza virus were restricted to South Korea, China and Thailand. It was initially identified in dogs in Asia in 2006-2007 and likely arose through the direct transfer of an avian influenza virus to dogs, possibly from among viruses circulating in live bird markets. The cases of canine H3N2 influenza reported all over the United States have been almost genetically identical to canine H3N2 viruses previously only reported in Asia.

How would my dog contract canine influenza?

Canine influenza is transmitted through airborne respiratory secretions from coughing, barking and sneezing. The dogs most at risk of being infected are those in close contact with other dogs in places such as boarding kennels, dog shows, training classes, day-care facilities, shelters, dog parks and groomers.

Dog flu can also be spread indirectly through objects, such as kennels, food and water bowls, collars and leashes. It can also be transmitted by people who have been in contact with infected dogs. It is important to clean and disinfect objects that have been in contact with an infected dog to avoid exposing other dogs to the virus. Likewise, people who have been in contact with an infected dog should wash their hands and clean their clothing to avoid spreading the virus.

The canine influenza virus can remain alive and infectious on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours. H3N8 has an incubation period of one to five days, with clinical signs in most cases appearing two to three days after exposure. Dogs infected with H3N2 may start showing respiratory signs between two and eight days after infection.

Dogs are most contagious during the incubation period and shed the virus even though they are not showing signs of illness. Some dogs may not show signs of illness, but have a “subclinical” infection and shed the virus.

What are the signs of canine influenza in dogs?

The signs of canine influenza are cough, runny nose, fever, lethargy, eye discharge and reduced appetite. However, not all dogs will show signs of illness. The severity of the infection can range from no symptoms at all to severe illness resulting in pneumonia and sometimes death.

Most dogs recover within two to three weeks. Canine-influenza infections compromise the normal defense mechanisms of the canine respiratory tract. Some dogs develop secondary bacterial infections, which could lead to more severe illness. Dogs may cough for several weeks after infection, but they are not contagious at this time. Dogs are generally free of canine influenza by seven days following the onset of clinical signs.

How is canine influenza diagnosed?

Canine influenza cannot be diagnosed solely by the clinical signs of coughing, sneezing and nasal discharge. These symptoms are also present with other canine respiratory illnesses such as canine infectious tracheobronchitis, also known as kennel cough.

The diagnosis of canine influenza requires the identification of the viruses in the infected dog or the detection of antibodies in the blood in the later stages of the infection. Tests are available to diagnose and identify the strains of canine influenza virus.

At the present time, the most reliable way to diagnose canine influenza virus infections is by blood tests that detect the presence of antibodies specific to the virus. Paired samples are preferred, with the first sample collected at the first sign of infection, and the second sample taken two to three weeks later.

A PCR test is used to directly detect the virus. This test is run on nasal swabs or respiratory tissue and will detect the DNA of specific viruses. Broad screening tests should be used to avoid missing a potential influenza infection caused by another strain of the flu.

Isolation of the canine influenza virus is an unreliable way to confirm infection. The reason for this is not clear, but the timing of the sample collection may be the key. Nasal swabs are nearly twice as successful in isolating the virus as swabs taken from the throat of the same dog at the same time.

What is the treatment for canine influenza?

The treatment for dogs with canine influenza largely consists of supportive care. This includes keeping the patient hydrated and controlling the cough while the body’s immune system fights off the virus. Broad spectrum antibiotics may be prescribed to treat a secondary bacterial infection.

Most dogs recover from canine influenza within two to three weeks. To prevent transmission of the virus, infected dogs, as well as other dogs in the household, should be isolated for four weeks.

Owners and professional personnel are advised to clean and disinfect all clothing and shoes, equipment, surfaces and hands after exposure to dogs showing signs of respiratory disease. Personal protective equipment, such as gowns, gloves and masks, can be worn when handling sick dogs.

Dogs that are coughing or showing signs of respiratory disease should not participate in activities with other dogs to avoid exposing other dogs to the virus.

Is there a vaccine for canine influenza?

Vaccines are available for both H3N8 and H3N2 strains of canine influenza. A bivalent vaccine that offers protection against both strains is also available. The initial dose is followed by a booster in two to four weeks, with annual revaccination recommended.

While vaccination can reduce the risk of a dog contracting canine influenza, it may not totally prevent an infection. However, dogs that are vaccinated usually have a milder illness and a quicker recovery.

The canine influenza vaccine is a “lifestyle” vaccine. It is not necessary for every dog. The vaccine is intended to protect dogs at risk for exposure to the virus. This includes dogs that participate in activities with other dogs such as shows, trials and doggy day care, or are housed in communal facilities where the virus is easily spread. Dogs that may benefit from canine-influenza vaccination include those that receive the Bordetella/parainfluenza kennel-cough vaccine, because the risk groups are similar.