Linda Simon
Dr Linda Simon (MVB MRCVS, University College Dublin)
Sick pup with Canine Influenza

While us humans are more than familiar with the flu and may be unlucky enough to catch what’s going around every few years, dogs seem naturally more resistant and it is actually not as common as one may assume for dogs to develop Canine Influenza. That being said, it is certainly not unusual for a dog to become unwell after being exposed to the virus and those that spend a lot of time around other dogs (such as in kennels or pounds) are most at risk.

It’s important that owners do not assume that any runny nose, cough or sneeze is attributed to Canine Influenza as there are many other conditions that can cause similar symptoms in dogs, including kennel cough, tracheal collapse and heart disease. Due to this, any new flu-like symptom always warrants a trip to the vet.

For most who catch the flu, their prognosis is excellent. Some (an estimated 20%) will not show any symptoms or may be very mildly affected. Dying from Canine Influenza is possible (particularly in debilitated animals) but is not something that happens often.

What Is Canine Influenza?

Sick Jack Russell Terrier

Canine Influenza or ‘dog flu’ is a viral infection and it is a highly contagious disease that can be spread from dog to dog. The strains that we see in the canine population are H3N2 and H3N8. Interestingly, while both of these strains pass from dog to dog, the H3N2 originally only affected birds and the H3N8 strain was a horse pathogen.

Relatively new pathogens, the H3N2 strain of the virus was first recognised in Asia in 2007 and the H3N8 strain was first identified within the USA in 2004. These viruses evolved over time to be able to affect our canine companions. While interesting to know, in reality we will rarely check which strain an animal has as it will not affect their treatment plan.

How Do Dogs Catch It?

Pack of Dogs in Park

The Canine Influenza virus is highly contagious and can be spread relatively easily from dog to dog. The virus is present in fluid droplets that are expelled from the body through coughing, barking and sneezing and become airborne. Animals may either become exposed to these particles from contaminated items (such as when they share food bowls) or from direct contact (for example if they are sneezed on!).

Humans can play a big role in the spread of the disease if they come are around an affected dog and then do not practice strict hygiene (including decontamination of objects and surfaces, as well as hand washing) before coming into contact with other dogs.

Where Is It Most Commonly Found?

Due to the high concentration of dogs and the ease with which aerosolised droplets can spread, any area that will have dogs in close contact with one another is at risk of an Influenza outbreak. It would just take one affected animal to lead to an outbreak that affects everyone. The Influenza virus is most commonly found in veterinary clinics, grooming centres, boarding kennels, rehoming centres and pounds.

What Are the Symptoms?

The symptoms of Canine Influenza are by no means specific so a dog suffering from these symptoms does not necessarily have flu and may well have another infection or disease, such as Kennel Cough. Symptoms include:

  • Sneezing
  • Runny Nose
  • Runny Eyes
  • Cough
  • Reluctance to Exercise/Socialise
  • Reduced Appetite
  • Fever

It is important to remember that some dogs will show few if any symptoms despite harbouring the virus and acting as a source of infection to others. It is also worth mentioning that secondary bacterial infections are not uncommon, as the respiratory system is impaired when infected and cannot fight off other infections as well as it normally would.

This can result in more serious symptoms and a more unwell patient. When a secondary bacterial infection affects the lower respiratory tract, animals can go on to develop pneumonia, which can be particularly risky for the young, old and unwell.

How are Dogs Diagnosed

Puppy at Vets

As there are a number of conditions that can mimic Canine Influenza, it is not always immediately obvious that a dog has the flu and the vet may need to run several tests when presented with a dog that is showing symptoms, such as coughing and/or sneezing. As well as a physical exam, most will have a blood test to check for changes, such as an increase in the number of their white blood cells.

Chest X-rays are frequently undertaken as they can help to check for secondary issues, such as pneumonia. Some vets will also perform a diagnostic test called a broncho-alveolar lavage to sample the cells within the respiratory tract. None of these tests are specific for flu. There are test which can be performed in the laboratory, such as a blood test for antibodies and a PCR test for the viral DNA, though these can be quite expensive and are not 100% reliable.

What Is the Treatment?

It is important to emphasise that antibiotics play no role in the treatment of a straight-forward case of Canine Influenza, which is a viral and not a bacterial infection. Viral infections are typically treated with supportive care as the animal’s immune system will be able to fight the infection without medication. Some dogs need little to no treatment but others may require nursing to ensure they maintain their energy and hydration levels.

For some, they will have their noses and eyes gently cleaned with warm cotton wool every few hours. They may also be treated to steam baths. Limiting exercise and encouraging rest and sleep can aid in a quick recovery. Many vets will suggest a high calorie, nutrient dense diet, particularly if appetite is reduced. If an animal does become dehydrated, they may need to be admitted to the hospital to be placed on intravenous fluids while they recover their strength. If an animal were to develop a secondary bacterial infection, they would then be given a course of antibiotics.

How Long Do Dogs Remain Contagious For?

Frustratingly, dogs can be contagious before even showing signs of the disease. This makes it far more difficult to control and can make it particularly tricky to prevent outbreaks in places such as rehoming centres and kennels. Once a dog catches the flu, they will not show any symptoms for roughly two to four days.

It is on about the fourth day that the level of the virus that they shed begins to decrease but we know that they can still pass the virus on for at least one week after this. In fact, studies have shown that those affected with the H3N2 strain remain contagious for far longer than this and often up to several weeks.

Will I Need to Quarantine my Dog?

Jack Russell Terrier Taking a Nap

Whether your dog has received a definitive diagnosis of Canine Influenza or not, any dog showing symptoms that could be classified as ‘flu-like’ should be kept away from other dogs. It is an owner’s responsibility to prevent their dog from interacting with other dogs and from going to areas where they could endanger others, such as the groomers or a dog park.

For those who own more than one dog, they should assume that all have been exposed to the virus and are carrying it (whether showing symptoms or not), so the same rules should apply to all of the dogs in the household. The rule of thumb is that those affected with the H3N8 strain are isolated for seven days and those who have the H3N2 strain should be isolated for 21 days. If it is unknown which strain a dog has, it should be assumed that the 21-day isolation period is needed.

What Is the Recovery Time?

The effects of Canine Influenza can last for several weeks. The overall recovery time depends on which strain the dog has contracted and on how fit and healthy the dog is otherwise. Good supportive care can reduce the amount of time that dogs remain under the weather for.

Preventing Dog Flu

When everyone works together (pet owners, business owners and animal health professionals alike), we can reduce the spread of the disease and greatly limit any outbreaks.

Close to Home

Though there is no way to completely eliminate the risk of a dog catching Canine Influenza, there are things that owners can do to reduce the odds. Avoiding places where there will be a high volume of dogs, such as dog parks or doggy day cares, is sensible though is not always possible for every owner. In reality, limiting exposure by only using these facilities when necessary is a more practical solution.

Owners should be vigilant and cautious when out on a walk or around other dogs and any dog showing symptoms that could indicate they are carrying flu should be given a wide berth. Owners should prevent their dogs from getting too close to them or from having contact with anything they have touched e.g. a ball or toy.

Owners should also try to keep up to date with local happenings as outbreaks within the community may be reported, for example, in local social media groups, in community newspapers or on posters in the park. Being aware of an outbreak allows owners to take the necessary precautions and can potentially reduce the risk of the disease spreading further.

In Canine Facilities

Limiting Canine Influenza in facilities, such as veterinary clinics and boarding kennels, is essential to safeguard the population. This may mean veterinary clinics using separate waiting areas for those showing symptoms of flu and employing screening programmes when dogs are admitted to a boarding facility.

On top of this, staff should be trained to practice good hygiene at all times. Any animal showing symptoms of the flu should be immediately isolated and barrier nursed using the appropriate personal protective equipment.

Is There a Vaccine?

Corgi Getting Vaccination

Vaccination is considered the best form of prevention. Not every country will have a vaccine available, though the USA does. Dogs are typically vaccinated against both the H3N2 and H3N8 strains. Vaccines require ‘top-ups’ two to four weeks after they are initially given and need to be repeated annually to ensure antibody levels do not drop too low.

While it is true that any dog can become infected, not every animal is routinely vaccinated. Owners of those dogs who spend a lot of time around other dogs, such as those who compete athletically or participate in dog shows, should consider the vaccine. Similarly, some boarding kennels may request that each dog that attends is vaccinated, to reduce the chance of them experiencing an outbreak at their facility.

Are Humans at Risk of Infection?

Thankfully, there is currently no risk of humans contracting Canine Influenza. However, Influenza is a clever virus that has the ability to mutate and potentially infect mammals that it could not in the past.

This has already happened in the case of Swine Flu, for example. For now, there have not been any reports published of a human contracting either the H3N8 or the H3N2 strain of this disease, but we remain vigilant and cautious.