The Canine Ledger

Kennel Cough: When to Wait, When to Worry, and the 2023 Outbreak

Most kennel cough clears up in about 10 days without antibiotics. The signs that mean it isn't simple, and what the 2023 'mystery illness' turned out to be.

Written by thecanineledger

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The international guidelines on antibiotics for respiratory disease in dogs say that most cases of kennel cough don’t need them. “Most dogs with clinical signs of CIRDC including mucopurulent nasal discharge maintain normal appetite and attitude and might resolve spontaneously within 10 days without antimicrobial treatment” (Lappin et al., ISCAID guidelines, Journal of Veterinary Internal Medicine 2017). CIRDC is the canine infectious respiratory disease complex, the vets’ name for kennel cough.

That surprises many owners, who expect a cough to mean a course of tablets.

While most dogs with kennel cough get better on their own, a few develop pneumonia, and puppies and older or ill dogs are more at risk. This page sets out the normal course, the signs that mean your dog should be seen, and what the 2023 “mystery dog illness” in the US turned out to be.

1. What kennel cough is

Kennel cough isn’t one infection. The Merck Veterinary Manual’s owner page explains that “A number of viral and bacterial organisms can cause kennel cough. It is common to have infections with more than one of these organisms at the same time” (Merck, Tracheobronchitis (Bronchitis) in Dogs).

It “spreads rapidly among susceptible dogs housed in close confinement, such as veterinary hospitals or kennels.” Despite the name, dogs can catch it anywhere dogs meet.

The ISCAID guidelines note that “The majority of cases of CIRDC are currently believed to be viral in etiology and so antimicrobial administration is often not indicated.” Antibiotics don’t treat viruses.

2. The normal course

The cough. Merck: “The most common sign is spasms of harsh, dry coughing, which may be followed by retching and gagging.” Many owners think their dog has something stuck in the throat.

How long. “The severity of the cough usually diminishes during the first 5 days, but the disease persists for 10 to 20 days.”

Otherwise well. “Affected dogs have few if any additional signs except for some loss of appetite.”

Keep them home. Merck advises that “In most cases, affected dogs should not be hospitalized because the disease is highly contagious and because it generally improves on its own.” Phone your vet before going in, so they can keep your dog away from other patients.

Our note: We couldn’t find a figure for how long to keep a dog with kennel cough away from other dogs. Ask your vet.

3. When to worry

The guideline’s line. The ISCAID Working Group recommends that antibiotics be considered within the 10-day observation period “only if fever, lethargy, or inappetence is present together with mucopurulent discharges.” Mucopurulent means thick, cloudy or green-yellow.

Merck’s warning signs. “Development of more severe signs, including fever, pus-containing nasal discharge, depression, loss of appetite, and a productive cough, especially in puppies, usually indicates the presence of an additional infection such as distemper or bronchopneumonia.” It adds that kennel cough “can progress to fatal bronchopneumonia in puppies or to chronic bronchitis in weakened, ill, or aged dogs.”

See your vet the same day if your dog:

  • is off food, or very quiet and tired
  • has a fever, or thick, coloured discharge from the nose
  • has a wet, productive cough
  • is a young puppy, elderly, or has heart or lung disease

Go now if your dog is struggling to breathe, breathing fast at rest, or has blue or grey gums.

Our note: The same-day and go-now lists are our wording, built from the Merck signs and the ISCAID threshold. Flat-faced breeds may need to be seen sooner.

Not all coughs are kennel cough. A cough in an older dog, or one that lasts beyond a few weeks, may be heart disease, a collapsing windpipe or chronic bronchitis. Merck defines chronic bronchitis as “a cough that persists for at least 2 months that is not due to any other respiratory disease.”

→ Heart Failure at Home: Counting Your Dog’s Sleeping Breaths · → Emergency Signs in Dogs: When to Go Now, Not Tomorrow

4. Canine flu

Canine influenza can look the same as kennel cough. Merck’s owner page notes that “most dogs (80%) develop a mild respiratory infection and have a cough that lasts 1–3 weeks.” Some become severely ill with high fever and pneumonia. Merck says “Less than 10% of affected dogs die because of the flu.”

Merck also says that “around 20% of infected dogs can still spread the virus without showing any signs.” It reassures owners that “there is no evidence to suggest that canine influenza virus can spread from dogs to people.” (Merck, Canine Influenza (Flu))

Our note: Merck’s “less than 10%” death figure is vague, and the page was last fully reviewed in June 2018.

5. The 2023 “mystery illness”

In the winter of 2023–2024, the United States “experienced a noticeable increase in cases consistent with CIRDC”, and the idea of a new disease spread quickly. Two laboratory studies have since looked for a new cause.

No new pathogen found. One study tested 50 samples from dogs in six US states, taken between December 2023 and February 2024. It found the usual causes, mostly Mycoplasma bacteria, and concluded that the cases “were not associated with the emergence of any new pathogens” (Thieulent et al., Frontiers in Veterinary Science 2025).

The suspected bacterium wasn’t there. Preliminary genetic investigations had claimed to find traces of a poorly understood bacterium called IOLA. A 2026 study screened 777 canine respiratory samples, and “Dual-target PCR identified no evidence of IOLA in respiratory samples from the 2023 aCIRD outbreak” (Hasan et al., Frontiers in Veterinary Science 2026). Its authors recommend “prioritization of established CIRD pathogens over unverified organisms.”

That doesn’t mean the dogs weren’t ill. The 2026 study describes the outbreak as “associated with high case-fatality rates and poor antibiotic response”. But the evidence so far points to familiar infections, not a new one.

Our note: The “high case-fatality rates” line is the 2026 paper’s description. It gives no figure in the passage we read.

6. Vaccines

Merck notes that “Vaccines are available to protect against distemper, parainfluenza, canine adenovirus-2, and Bordetella bronchiseptica, some of the main organisms responsible for kennel cough.” Some are core vaccines and some are not. Ask your vet which suit your dog’s lifestyle, for example if your dog goes to kennels, day care or classes.

→ Core and Non-Core Vaccines: What the 2024 WSAVA Guidelines Say · → Does Diarrhoea Need Antibiotics? What the Evidence Says

7. What we could not verify

Commonly saidWhat we found
“Kennel cough needs antibiotics”Usually not. The ISCAID guidelines say most cases may resolve within 10 days without them.
“Only dogs in kennels get it”No. It spreads wherever susceptible dogs are in close contact.
“The vaccine means my dog can’t get it”Not shown. Kennel cough has many causes, and vaccines cover some of the main ones.
“The 2023 illness was a new disease”No new pathogen has been found in the two studies we read.
“Dogs can give flu to people”Merck says there is no evidence that canine influenza spreads to people.

Sources

Always confirm with your vet before acting on anything on this page.