Mumps is an acute disease of children and young adults, caused by a paramyxovirus of which there is only a single serotype. Mumps virus produces no symptons in about one-third of infected people. In those with a clinical response, glandular and nerve tissue are most often affected. The most common signs are fever and swelling of the parotid glands. Other complications, which may appear simultaneously with these signs or in any sequence, are epididymo-orchitis, meningo-encephalitis, cranial nerve involvement (especially eighth cranial nerve damage leading to hearing impairment), pancreatitis, oophoritis, mastitis and myocarditis. Frequent viruria and abnormal renal function suggest that mumps virus may infect the kidneys. In some instances, one or more of the other implications may be present in the absence of parotitis.

The most common complication of mumps in children is meningitis, sometimes associated with encephalitis, and in young adults orchitis. Most complications due to mumps infection resolve without permanent damage. Death following mumps is rare and is mostly due to mumps encephalitis. Many people reach adulthood without developing immunity and potential target populations for immunization therefore include both children and susceptible adults.

The Requirements for Mumps Vaccine (Live) were adopted by the WHO Expert Committee on Biological Standardization in 1992.

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