Kennel cough is like a cold in humans. It is viral and passed from one dog to another, usually when they are in confined quarters like a kennel or vet's office, thus the name kennel cough. There are so many different strains of cough, the vaccines given really don't help.
It's hard to say how, it is an infection Bordetella bronchiseptica, and usually passed easily when dogs are grouped together, but not necessarily, like human coughs, however, they need treatment.
Kennel cough is a highly contagious infection of the dog's upper respiratory tract. It is spread readily from dog to dog. A dog who was infected and has recovered can still spread the disease for as long as 3 months after symptoms have disappeared. Kennel cough can result from a viral or bacterial infection, often both.
This is caused by bacterial infections. It can be linked to the flu in humans and can also be a symptom of another disease that your pet is suffering from.