Dogs get kennel cough by inhaling airborne droplets from an infected dog’s cough or sneeze, through direct nose-to-nose contact, or by touching contaminated objects like shared water bowls, toys, or bedding. It’s not a single disease but a collection of infections caused by several bacteria and viruses working together, which is why veterinarians formally call it canine infectious respiratory disease complex (CIRDC). Any place where dogs gather in close quarters creates the perfect conditions for spread.
The Pathogens Behind It
Kennel cough isn’t caused by one germ. The most common culprits are a bacterium called Bordetella bronchiseptica and two viruses: canine parainfluenza virus and canine adenovirus type 2. Dogs frequently pick up more than one of these at the same time, and co-infections with all three are the most typical pattern. Bordetella is especially important because it can act as a primary pathogen on its own, particularly in puppies under six months old. The viruses often do the initial damage to the airway lining, which then lets bacteria move in and cause a deeper infection.
Other organisms sometimes involved include canine herpesvirus, canine influenza, and a type of bacteria called Mycoplasma, though their role is less clearly established.
Three Ways Dogs Catch It
The most efficient route is airborne. When an infected dog coughs or sneezes, it launches tiny droplets loaded with bacteria or viral particles into the surrounding air. A nearby dog breathes those in, and the pathogens land directly on the lining of the windpipe and upper airways. This is why infections tear through enclosed spaces so quickly.
Direct contact is the second route. Dogs that greet each other by licking, nuzzling, or sniffing faces are essentially exchanging respiratory secretions. Even brief encounters at a dog park can be enough if the other dog is actively shedding.
The third route is contaminated surfaces. Shared water bowls, toys, bedding, kennel walls, and even people’s hands can carry infectious droplets. A dog that drinks from the same bowl or mouths the same toy as a sick dog is at real risk.
What Happens Inside the Airway
The lining of a dog’s windpipe and bronchial tubes is covered in tiny hair-like structures called cilia. These cilia constantly wave in coordinated patterns, pushing mucus and trapped debris up and out of the airways. It’s essentially a self-cleaning escalator for the lungs.
Bordetella produces toxins that destroy this system. These toxins trigger inflammation, kill off the ciliated cells, and cause the airway to produce excess mucus it can no longer clear. The result is a raw, irritated trachea with no functioning defense against further infection. That’s what produces the characteristic honking cough: the airway is inflamed and stripped of its protective layer, so every breath of air or slight pressure on the throat triggers a coughing reflex. The toxins also break down the tight seals between airway cells, making the tissue more permeable and vulnerable to secondary bacterial infections.
Where Dogs Are Most Likely to Get It
Any setting with multiple dogs in close proximity is high risk. The classic locations include boarding kennels, dog daycare facilities, shelters, grooming salons, veterinary waiting rooms, and dog shows. The risk climbs when dogs are confined together for longer periods, sharing the same air supply in enclosed or poorly ventilated spaces. A single afternoon at daycare carries less risk than a week of boarding, though both can be enough.
Dog parks and training classes are moderate-risk environments. They involve shorter exposure times and open air, but direct contact between dogs still happens freely. Even a neighborhood walk can lead to infection if your dog greets a sick dog along the way.
How Long a Sick Dog Stays Contagious
This is one of the trickiest parts of kennel cough. Dogs infected with Bordetella can remain contagious for up to eight weeks after their symptoms resolve, and possibly longer. That means a dog that seems completely recovered, with no coughing or nasal discharge, can still shed bacteria and infect other dogs for two months or more. This extended shedding window is a major reason kennel cough is so hard to contain in multi-dog environments. A dog that “got over it” weeks ago can introduce the infection to a new group.
What It Looks and Sounds Like
The hallmark symptom is a dry, forceful cough that sounds like a goose honk. Many owners initially think their dog has something stuck in its throat. The cough is often triggered by excitement, pulling on a leash, or light pressure on the trachea. Most dogs remain alert and continue eating normally, which can make the illness seem minor.
In mild cases, the cough lasts one to two weeks and resolves on its own. More severe infections, especially those involving multiple pathogens or affecting puppies, senior dogs, or dogs with compromised immune systems, can progress to lethargy, loss of appetite, fever, and thick nasal discharge. Pneumonia is the most serious complication and requires veterinary treatment.
Vaccination and Prevention
Bordetella vaccines come in two main forms. The intranasal (or oral) version uses live but weakened bacteria and provides protection after a single dose. It’s squirted into the nose or mouth and stimulates immunity right at the site where infection starts. The injectable version uses killed bacteria and requires two doses given two to four weeks apart to build full immunity. These two types are not interchangeable: the injectable form should never be given intranasally, as it won’t work and can cause discomfort.
Vaccines reduce the severity and likelihood of infection, but they don’t guarantee complete protection. Because kennel cough involves multiple different pathogens, a dog vaccinated against Bordetella can still catch the disease from one of the viral causes. Most boarding facilities and daycares require proof of Bordetella vaccination precisely because it lowers the overall risk of outbreaks, even if it can’t eliminate them entirely.
Beyond vaccination, practical steps help. Bringing your own water bowl to the dog park, avoiding shared toys in group play settings, and keeping your dog away from dogs that are actively coughing all reduce exposure. If your dog develops a cough after being around other dogs, keeping them isolated from other pets for several weeks protects the dogs around you.