Fri, 03/03/2023 - 5:51am

Canine Influenza

How to identity, treat and prevent this respiratory virus

What is canine influenza?


You have probably heard there have been outbreaks of canine influenza recently, especially in the Philadelphia area. This is a concern for all of us with dogs that frequently interact with other dogs.

Canine influenza, or dog flu, is a highly contagious viral infection that affects dogs and also cats. It is a Type A influenza virus and is further identified based on the composition of two specific proteins in the lipid outer layer of the capsid. These are hemagglutinin (HA) and neuraminidase (NA). At this time, two strains of canine influenza virus have been identified in the United States: H3N8 and H3N2.

Influenza viruses are able to quickly change, or mutate, and give rise to new strains that can infect other species. Both strains of canine influenza identified in the U.S. can be traced to influenza strains known to infect species other than dogs. At some point, these viruses acquired the ability to infect dogs and be transmitted from dog to dog.

Canine H3N8 influenza was first identified in Florida in 2004 in racing Greyhounds. It is thought this strain developed from an equine H3N8 influenza strain that jumped from horses to dogs.

Canine H3N2 influenza was first identified in the U.S. in 2015 following an outbreak of respiratory illness in dogs in the Chicago area. Prior to this, reports of canine H3N2 influenza were restricted to South Korea, China and Thailand. It was initially identified in dogs in Asia in 2006 and likely arose through the direct transfer of an avian-influenza virus, possibly from among viruses circulating in live-bird markets, to dogs.

In early 2016, following the initial diagnosis in Chicago, a group of shelter cats in Indiana was diagnosed with H3N2 canine influenza. It is believed the virus was transmitted to them from infected dogs.

Canine-influenza viruses are not thought to pose a threat to people. There is no evidence that either strain of canine influenza (H3N8 or H3N2) can infect humans.


How would my dog become infected with canine influenza?


Canine influenza is transmitted from dog to dog by coughing, sneezing and barking. Secretions from the respiratory tract containing the virus are passed in the air and breathed in by nearby dogs. The virus is easily spread in places where dogs are in close contact with each other. Dogs at boarding kennels, dog shows, training classes, groomers, day-care facilities and shelters are at increased risk of infection.

The canine-influenza virus can also be spread indirectly through objects, such as food and water bowls, kennels, collars and leashes. People who have been in contact with infected dogs may also spread the virus. It is important to clean and disinfect objects that have been in contact with an infected dog to avoid exposing other dogs. Likewise, people should wash their hands and change their clothes after being in contact with an infected dog.

The virus can remain alive and infectious on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours. It is important to practice strict cleaning and disinfection procedures to reduce the risk of disease transmission.

The H3N8 virus has an incubation period of one to five days, with clinical signs appearing two to three days after exposure in most cases. Dogs infected with the H3N2 virus 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.


What are the symptoms of canine influenza?


Canine-influenza virus infects and multiplies inside the cells of the respiratory tract from the tip of the nose to the end of the airways in the lungs. The body’s inflammatory response to the disease results in the death of the cells lining the respiratory tract. This leaves the respiratory tract vulnerable to secondary bacterial infections that result in coughing and snotty discharge from the nose.

The majority of dogs have mild symptoms of canine influenza. The most common sign is a cough that persists for 10 to 21 days despite treatment with antibiotics and cough suppressants. Discharge from the nose and eyes, sneezing, lethargy and loss of appetite may also be observed.

Some dogs are more severely affected and will develop signs of pneumonia, such as a high fever of 104oF to 106oF and labored breathing. Although most dogs recover from canine influenza, deaths due to the H3N2 strain have been reported.


How is canine influenza diagnosed?


Your veterinarian can test your dog to diagnose and identify the strain of canine influenza, since the signs of canine influenza are the same as other respiratory diseases. The PCR, which stands for polymerase chain reaction, will detect the presence of the virus and seems to be the most reliable test for the diagnosis of canine influenza. Other tests are virus isolation, immunoassays to detect virus antigen, and serology for antibodies specific to the virus.


What is the treatment for canine influenza?


The treatment for canine influenza, as for most viruses, is mostly supportive. Good care and nutrition help dogs mount an effective immune response. Most dogs recover from canine influenza in two to three weeks.

More diagnostic tests and treatments may be necessary in cases where secondary bacterial infections, pneumonia or dehydration are present. Dogs that have other health factors, such as pre-existing lung disease, immunosuppression, tracheal collapse or pregnancy, may require additional care. These treatments include antibiotics for secondary infection, non-steroidal anti-inflammatory medication to reduce fever and inflammation, and electrolyte fluids to correct and maintain hydration.

In order to prevent transmission of the virus, dogs infected with canine influenza should be isolated for four weeks. This applies to other dogs in the household as well.

Antiviral drugs prescribed to treat influenza are approved for use in humans only. Little is known about their effectiveness and safety when given to dogs.


How can I protect my dog from catching canine influenza?


Vaccines are available for both the H3N8 and H3N2 strains of canine influenza, either separately or the bivalent vaccine that contains both strains. Vaccination will reduce the risk of a dog contracting canine influenza. It may not completely prevent an infection, but it may reduce the severity and duration of the illness.

The canine-influenza vaccines are not necessarily recommended for every dog. They are more of a “lifestyle” vaccine. The vaccine is intended to protect dogs at risk for exposure to the canine-influenza virus. This includes dogs that participate in activities with many other dogs or are housed in communal facilities.

Dogs that may benefit from canine-influenza vaccination include those dogs that receive the Bordetella/parainfluenza vaccine for kennel cough, since the risk groups are similar. You should consult your veterinarian to determine your dog’s level of risk and if vaccination is appropriate.


Is canine influenza the same as kennel cough?


No. Canine influenza is a viral disease, whereas kennel cough, or infectious tracheobronchitis, is a combination of a bacterial and viral infection. Kennel cough is easier to treat than canine influenza since the bacterial portion of the infection responds to antibiotics. Viral diseases rely on the body’s immune system and supportive therapy to fight off the disease.



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