Kennel Cough is the catch-all term used to refer to infectious
tracheobronchitis. The most common cause (there are
multiple causes, in cats dogs and people) in dogs is canine adenovirus
II.

If you take a dog with no other pathogens and give it one of these three
organisms, it will get kennel cough: canine adenovirus II, parainfluenza,
and bordetella bronchiseptica. In nonexperimental situations, more than
one is commonly involved. When the animals have the organisms, they show
signs or they don't - but they are't carriers, or latently infected, or
anything. And they don't get bacterial superinfections. It's usually just
these organisms.

Usually the animals get infected, get sick, then clear the infection. One
animal can get reinfected with the same disease, though. That's from
reexposure and reinfection, not from recrudescence of a latent infection.
These organisms cause only mucosal inflammation, no real damage to the
airway.

So, basically, the clinical presentation of kennel cough is a coughing
healthy dog. It's a nonproductive cough because there is no bacterial
component or damage. No nasal or ocular d/c - these organisms only inflame
the trachea. Also no systemic signs - eating, drinking, sleeping, etc all
normal, no fever. The thing you will see on your physical is an easily
elicited spasm of coughing from tracheal pressure - instead of the usual
one or two coughs, he'll cough for a while, a whole bout of coughing.
Sometimes just being at the vet will trigger the coughing. or owners may
say "new animal just arrived" or he just came from the kennel, or was
exposed to another coughing dog 2-6 days ago - the incubation period is
2-6 days. There is a low grade fever but it occurs prior to the onset of
the coughing. And people do not always give you that history.

In order to dx definitively - well, you
don't. The thing you'd have to do to dx viruses is viral culture - that's
not routine. If there is an extreme situation, maybe, but really that's a
research tool. By the time you got results, animal would be better. for
bordetella, you can dx by transtracheal wash, pretty routine procedure -
that's diagnostic if you get a pure culture of bordetella. but really,
you generally watch the animal and see what the clinical course is like.
If signs start to wane in 1-3 wks, it probably was kennel cough.
Sometimes, if you have an animal coughing and showing no other signs, and
it goes on a month or two, you will then do a further workup. Sometimes
bordetella by itself can last for months. you dx by transtracheal wash
and obtaining pure culture and sensitivity - sometimes requires prolonged
1-2 mos abx administration.