One infection with the mumps virus usually provides lifelong immunity. Although the mumps virus initially affects the salivary glands, the virus can easily enter the blood stream and spread to other body organs. This may cause many different types of complications. About 1 in every 400 to 6,000 people with mumps develops encephalitis . In boys, mumps can also attack the testicles .
Mumps can also cause complications that affect the ovaries, pancreas, kidneys, joints and eyes.
It is also an important cause of one-sided hearing loss, since it can attack the nerve that carries sound messages from the ear to the brain. The parotid glands become increasingly swollen and painful over a period of 1 to 3 days. In 2 of 3 cases, both the left and right parotid glands are affected. The second gland usually swells about 4 to 5 days after the first. In many children, other groups of salivary glands around the mouth and neck may also be attacked by the mumps virus.