Give 1mg of Benadryl per pound such that if your dog weighs 30 pounds, you should give it 30 mg of Benadryl. Talk your veterinarian - while antihistamines are generally safe, there are the potential for side effects particularly if your dog has chronic organ failure (renal failure, liver failure, congestive heart failure, etc.).
1 Encephalitis is inflammation of the brain.  Meningitis is inflammation of the membranes (called meninges) that surround the brain and spinal cord.
An acute infectious and contagious disease caused by a mumps virus of the genus Rubulavirus and characterized by fever, inflammation, and swelling of the parotid gland, and sometimes of other salivary glands, and occasionally by inflammation of the testis, ovary, pancreas, or meninges.he mumps infection can spread into the brain causing inflammation of the brain (encephalitis). Symptoms of mumps encephalitis include the inability to feel pain, seizures, and high fever. Encephalitis can occur during the parotitis stage or one to two weeks later.