Mumps is the swelling of parotid salivary gland (one of the four salivary glands found in mouth just under each ear of the dog) in response to an infection by a virus (paramyxovirus).
The oral cavity of the dog has four sets of salivary glands which are the parotid, submandibular, sublingual, and minor salivary glands. These exocrine glands control the production and secretion of the saliva which in turn, breaks down starches into glucose for use by the body.
Dogs develop this condition when they are exposed to humans who have mumps. The mumps can be transmitted from humans to dogs. This is called a zooanthroponosis because it passes to animals (zoo) from humans (anthro). This cross-over is very rare, but is known to occur occasionally. When a dog does acquire an infection, the parotid salivary glands will swell in response.
Common symptoms of a dog being infected by mumps virus include
Lack of appetite
Swelling below the ears, caused by parotid salivary gland swelling