Canine Influenza: Dog Flu Explained
Dog flu is a highly contagious respiratory virus. Two strains exist, and vaccination protects against both.
Canine influenza, commonly called dog flu, is a contagious respiratory disease caused by influenza A virus. Two strains affect dogs: H3N8 (originally an equine virus that jumped to dogs) and H3N2 (originally an avian virus). Both cause coughing, fever, and respiratory distress, and both are now vaccine-preventable.
Key Points
- Two strains exist: H3N8 and H3N2; vaccines protect against both
- Dog flu spreads rapidly in kennels, shelters, dog parks, and grooming facilities
- Most cases are mild, but some develop pneumonia requiring hospitalization
- Virtually all dogs exposed become infected; 80% show clinical signs
- Cats can also be infected with H3N2
- Vaccination is recommended for social dogs and those in high-risk environments
How Dog Flu Spreads
Canine influenza spreads through respiratory droplets from coughing, sneezing, and barking. Direct contact with infected dogs is the primary route. Contaminated surfaces — food bowls, leashes, toys, and clothing — can also transmit the virus. The virus survives on surfaces for 48 hours and on clothing for 24 hours. Infected dogs shed virus for up to 28 days, even after symptoms resolve. This prolonged shedding makes outbreaks difficult to control.
Signs of Infection
The incubation period is 2-4 days. Mild cases show a persistent dry cough for 2-3 weeks, nasal discharge, low-grade fever, and lethargy. Some dogs develop a moist, productive cough with thick nasal discharge. Severe cases progress to pneumonia with high fever (over 104°F), difficulty breathing, and reluctance to move. Secondary bacterial infections are common. Unlike human flu, canine influenza is not seasonal — it can occur year-round.
Diagnosis
Clinical signs suggest canine influenza but cannot confirm it. Nasal or pharyngeal swabs tested by PCR detect viral RNA during the first 4 days of illness. Blood tests for influenza antibodies (serology) confirm infection but require paired samples 2-3 weeks apart. Chest X-rays identify pneumonia. Complete blood count may show low white blood cells early in infection. Respiratory panels using PCR can differentiate influenza from Bordetella, parainfluenza, and adenovirus.
Treatment and Prevention
Treatment is supportive — there is no specific antiviral for canine influenza. Mild cases need rest, hydration, and cough suppressants. Pneumonia cases require hospitalization with IV fluids, oxygen therapy, nebulization, and broad-spectrum antibiotics for secondary bacterial infection. Vaccination is available for both H3N8 and H3N2, either separately or combined. Dogs in boarding, daycare, shows, and shelters should be vaccinated. Good hygiene and isolation of sick dogs prevent outbreaks.
When to See a Vet Immediately
- Your dog has a persistent cough lasting more than a few days
- There's thick nasal discharge and difficulty breathing
- Your dog has a high fever and is lethargic
- Your dog was recently at a boarding facility or dog park
- Multiple dogs in your household are showing similar signs
How RVC Can Help
This article is for educational purposes only and does not replace professional veterinary advice. If your pet is showing any symptoms, please contact Royal Veterinary Center immediately at +853 6677 6611.