Since dogs have tonsils, they can also develop tonsillitis. Similar to lymph nodes, their job is to fight infection. When they are doing this, they may become infected themselves and will enlarge.
Chronic vomiting, a chronic productive cough, and chronic disease in the mouth will allow bacteria to infect the tonsils. The main cause of chronic disease in the mouth is tartar accumulation on the teeth and the bacterial infections associated with it. Occasionally, primary tonsillitis with no underlying cause will occur.
When the tonsils enlarge, they are usually quite painful. This causes the dog to gag, as if something is in the throat, or to make exaggerated swallowing motions. Some dogs appear to be licking their lips repeatedly. Most affected dogs are reluctant to eat because of the pain associated with swallowing. Many dogs with tonsillitis are not as active as normal, but they usually do not have fever.
If an underlying source of the infection can be found, it must be treated with antibiotics. If there is tartar and periodontal disease present, the teeth should be cleaned.
Most cases of tonsillitis are caused by bacteria that are found normally in the mouths of dogs and humans. Therefore, it is not contagious unless it is caused by an unusual bacterium.
It is not that common and more prevalent in small breeds of dogs than in large dogs.