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Dog Flu (Canine Influenza) in Dogs

What Is Dog Flu (Canine Influenza)?

Canine influenza virus (CIV), commonly known as dog flu, is a highly contagious respiratory virus that impacts dogs of all breeds and ages. While dog flu has been detected across most of the United States, fortunately, it rarely leads to fatalities in dogs and, for many, does not require a visit to the vet.

CIV is caused by two distinct types of influenza viruses: H3N2 and H3N8. Initially affecting other canine species, birds, and equines, both viruses now also affect dogs. While H3N2 can also affect cats, neither virus has been reported to infect humans.


As this is a respiratory virus, dogs will exhibit symptoms typical of respiratory illness and common flu-like indications, including:

  • Persistent dry cough lasting for weeks
  • Fever
  • Discharge from the nose and eyes
  • Sneezing
  • Reduced appetite
  • Lethargy or decreased vigor

In severe instances, dogs may develop secondary bacterial infections, experience high fever (>103.5 F), and even contract pneumonia, which can pose a threat to their life.

CIV is highly contagious among dogs. Research indicates that the virus can spread up to 20 feet through dogs’ respiratory droplets when they cough or sneeze. While this is the main mode of transmission, dogs can also contract the virus through contaminated food and water bowls, shared toys, leashes, and other items. Additionally, human contact, such as handling an infected dog and then interacting with other dogs, can indirectly spread the virus. After infection, it takes a few days for dogs to display symptoms, and they remain contagious for approximately four weeks. While any dog can become infected, those originating from shelters are particularly vulnerable.


CIV is categorized among influenza A viruses, which are classified into types based on their hemagglutinin (H) and neuraminidase (N) proteins. Typically, these viruses are species-specific, but through mutations and other alterations, they can affect different animals over time.

H3N8 and H3N2, the strains of influenza viruses observed in dogs, serve as notable examples. The H3N8 virus, initially identified in horses, was detected in the dog population of the United States in 2004. On the other hand, the H3N2 virus, which emerged in the United States in 2015, is believed to have originated from the Asian bird population. Fortunately, there is currently no evidence to suggest that humans can contract dog flu, or vice versa.


Diagnosing dog flu in dogs can be challenging since symptoms can resemble those of various respiratory infections. Therefore, it’s crucial to have your dog tested to ensure proper treatment. For CIV, veterinarians often conduct a PCR panel, involving obtaining a swab from your dog’s nose, conjunctiva, or pharynx, which is then sent to a laboratory for analysis of viral DNA. Additionally, veterinarians may recommend further testing such as bloodwork and chest radiographs to assess your dog’s overall health, hydration status, and to detect any signs of pneumonia, which can be life-threatening and requires prompt treatment.

Before visiting the veterinarian, it’s important to call ahead and inform them about your dog’s flu-like symptoms. This allows veterinarians to follow specific protocols and procedures to minimize the risk of transmission to other dogs.


Treating CIV in dogs primarily involves supportive measures. It’s crucial to ensure that your dog remains calm, gets plenty of rest, and stays hydrated to facilitate a speedy recovery. In a hospital setting, this may involve administering IV fluids, cough suppressants, and providing nutritional support. If there’s a secondary bacterial infection present, veterinarians often prescribe antibiotics like clavamox or doxycycline.

Dogs infected with CIV should be kept isolated from other dogs (and cats) as soon as symptoms appear and for the subsequent 4 weeks. This means avoiding activities such as visits to dog parks, boarding, grooming, and similar outings. Additionally, since the virus can spread through contaminated clothing, pet owners should refrain from interacting with other dogs (and cats) during this period to prevent further transmission.

Living and Management

Thankfully, numerous dogs recover from CIV without significant complications within a few weeks, often with minimal lasting effects. Your dog may continue to have a cough during this recovery period. However, younger or older dogs, as well as those with compromised immune systems, may suffer more severe symptoms such as pneumonia and could potentially succumb to the illness. Seeking veterinary care promptly at the onset of your dog’s illness is crucial to achieving the best possible outcome.


Thankfully, there exists a vaccine for dogs designed to shield them from both strains of CIV. Manufactured by Nobivac and Zoetis, this vaccine can be administered to puppies as young as 7 or 8 weeks old, followed by a booster shot 3 weeks later and subsequent annual doses. While rare, possible side effects include symptoms linked to hypersensitivity and allergic reactions, such as vomiting, diarrhea, facial swelling, hives, and in rare cases, shock and death. While not all dogs face the same risk of contracting the disease, those who frequent boarding or grooming facilities, doggie daycares, dog parks, dog shows, or other competitions are at higher risk.

It’s important to discuss your dog’s risk factors with your veterinarian, as well as the potential risks and benefits of vaccination. While vaccines may not guarantee complete immunity, they significantly reduce the likelihood of infection. In cases where infection does occur, symptoms are often milder, and the duration of illness is shorter.

Thankfully, the influenza virus is easily eradicated from the environment, often with common household cleaners like bleach and soapy water. It’s essential to wash your hands and clothing before interacting with any dogs, as well as between interactions with different dogs.

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