Canine influenza — commonly called dog flu — is a highly contagious respiratory virus that spreads rapidly wherever dogs gather: boarding facilities, dog parks, shelters, and groomers. In 2026, two strains remain active in the United States: H3N2 (the more prevalent strain) and H3N8. While rarely fatal in healthy dogs, dog flu can be serious for puppies, seniors, and immunocompromised dogs.
What Is Canine Influenza?
Canine influenza is caused by an influenza A virus adapted to infect dogs. Unlike the human flu, it's not seasonal — outbreaks can occur year-round. The virus spreads through respiratory secretions (coughing, sneezing, barking), contaminated surfaces, and direct dog-to-dog contact.
Virtually all exposed, unvaccinated dogs will be infected. Unlike many pathogens, dogs have little natural immunity to canine influenza. About 80% of infected dogs show symptoms; the remaining 20% are subclinical carriers who can still spread the virus.
Symptoms of Dog Flu
Mild to Moderate Cases (Most Dogs)
- Cough — soft, persistent, and productive; different from the honking cough of kennel cough
- Nasal discharge — initially clear, may become yellow or green with secondary bacterial infection
- Low-grade fever (103-104°F; normal is 101-102.5°F)
- Lethargy and reduced energy
- Reduced appetite
- Eye discharge
Symptoms typically last 2-3 weeks. Many dogs improve on their own with supportive care.
Severe Cases (About 20%)
A minority of dogs develop pneumonia — bacterial secondary infection of the lungs. Signs include:
- High fever (above 104°F)
- Rapid or labored breathing
- Productive cough with green/yellow discharge
- Significant lethargy — not getting up, not eating
- Blue-tinged gums (emergency sign)
Pneumonia from canine influenza can be fatal without treatment.
How Dog Flu Differs from Kennel Cough
This is the most common question owners ask. Both cause coughing after time at boarding or the dog park. Key differences:
- Kennel cough cough is typically dry and honking (like something's stuck in the throat); flu cough is softer and wet
- Flu usually causes fever and lethargy; kennel cough often doesn't
- Flu causes nasal discharge more prominently than kennel cough
See more about kennel cough in dogs and why dogs sneeze frequently for comparison.
When to Worry
Call your vet if your dog:
- Has a fever above 104°F
- Is breathing rapidly or with effort at rest
- Is significantly lethargic — won't get up or eat
- Has thick green or yellow nasal/eye discharge for more than 3-4 days
- Is in a high-risk group: puppy under 6 months, senior over 10 years, immunocompromised, or brachycephalic (flat-faced) breed
What to Do at Home
Isolate your dog. Canine influenza is highly contagious. Keep your dog away from other dogs for at least 21 days after symptom onset.
Rest and fluids. Encourage water intake and reduce activity.
Monitor temperature. A rectal thermometer is worth having — a fever above 103.5°F warrants a vet call.
Don't give human flu medications. Oseltamivir (Tamiflu) is not routinely recommended for dogs and should only be given under veterinary direction.
Inform your boarding facility or dog park. Other owners need to know so they can monitor their dogs.
How Voyage Can Help
Not sure if your dog has the flu, kennel cough, or something more serious? Voyage AI Vet can help you assess the symptoms and determine whether your dog needs same-day care or home monitoring — starting at $4.99/month.
Frequently Asked Questions
Q: Can my dog get the flu vaccine? A: Yes — bivalent vaccines covering both H3N2 and H3N8 are available. They don't prevent infection entirely but significantly reduce severity. Recommended for dogs that frequently board, go to dog parks, or attend shows.
Q: Can dogs give humans the flu? A: Current evidence suggests canine influenza strains do not readily infect humans. The risk of transmission from dogs to people is considered very low.
Q: How long is my dog contagious with dog flu? A: Dogs begin shedding virus before symptoms appear and remain contagious for up to 21 days after symptom onset. This is why early isolation matters.
Q: My dog was exposed at boarding but seems fine. Should I still be concerned? A: Yes — up to 20% of infected dogs are subclinical carriers. Keep them away from other dogs for 7-10 days after potential exposure and monitor for any symptoms.
Q: Is dog flu the same as kennel cough? A: No. Kennel cough (Bordetella) is a bacterial infection; canine influenza is a viral infection. They have overlapping symptoms but different causes, treatments, and timelines.
This article is for informational purposes only and is not a substitute for professional veterinary advice.