The name suggests a single illness contracted in boarding kennels. It is neither, and understanding what it actually is explains why it appears where it does.
A syndrome rather than one disease
The condition is produced by several agents, including more than one bacterium and several viruses, often acting together rather than alone.
Different combinations produce a similar picture, which is why the presenting cough looks the same regardless of what is responsible.
This is also why no single vaccine covers everything. Available vaccines target the most common contributors rather than the whole set.
How transmission happens
Spread is primarily through respiratory droplets and aerosol produced when an infected dog coughs, which travel effectively over short distances.
Shared water bowls, toys, bedding and surfaces provide a second route, and hands and clothing move material between dogs that never meet.
Confined shared air is the common factor across the settings where outbreaks occur, which includes kennels, day care, training classes, shelters and grooming premises.
Why outbreaks appear all at once
There is an incubation period of several days between exposure and the onset of coughing, during which a dog can already be shedding.
A group exposed on the same day therefore starts coughing at roughly the same time, days later, which produces the impression of sudden simultaneous infection.
Shedding also continues after the cough resolves, which is why dogs returned to a group too early restart the cycle.
The damage that causes the cough
The agents involved attack the cells lining the airway, including the ones carrying the fine hairs that clear mucus upward.
With that clearance impaired, irritant material accumulates and triggers the harsh, repetitive cough that characterises the illness.
The same loss of clearance leaves the lower airway more vulnerable to secondary infection, which is where complications arise in a minority of cases.
When it stops being straightforward
Most otherwise healthy adult dogs recover over a couple of weeks with rest and reduced exposure to irritants such as smoke and dust.
Puppies, elderly dogs, brachycephalic breeds and dogs with existing airway disease are at higher risk of progression to something more serious.
Loss of appetite, lethargy, difficulty breathing, fever or a cough that worsens rather than settling are reasons for prompt veterinary assessment. Calling ahead matters, since waiting rooms are exactly the environment the disease exploits.