Laboratory Diagnosis and Control of Mumps (Epidemic Parotitis)
Laboratory studies are not usually required to establish the diagnosis of typical cases. However, mumps can sometimes, be confused with enlargement of the parotids due to suppuration, foreign bodies in the salivary ducts, tumors, etc. In cases without parotitis, particularly in aseptic meningitis, the laboratory can be helpful in establishing the diagnosis.
Recovery of Virus
Virus can be isolated from saliva, cerebrospinal fluid, or urine collected within 4 days after onset of illness. After treatment with antibiotics, the specimen are inoculated into monkey kidney cell cultures. Virus growth can be detected in 5-6 days by adsorption of suitable erythrocytes by the infected cells. The isolate can be identified with specific antiserum that can inhibit the hemadsorption. Immunofluorescent serum can also identify a virus isolate in cell culture within 2-3 days.
Antibody rise can be detected in paired sera. The CF test is best for specificity and accuracy, although the HI test may be used. A 4 fold or greater rise in antibody titer is evidence of mumps infection. A CF test on a single serum sample obtained soon after onset of illness may serve for a presumptive diagnosis. S (Soluble) antibodies develop within a few days after onset and sometimes reach a high titer before V (viral) antibodies can be detected. In early convalescence, both S and V antibodies are present at high levels. Subsequently, S antibodies disappear more rapidly, leaving V antibodies as a marker of previous infection for several years. The intra-dermal injection of inactivated virus results in reappearance of V antibodies in high titer. Neutralizing antibodies also appear during convalescence and can be determined in cell culture.
Skin Test Antigen
Delayed type hypersensitivity may be noted about 3-4 weeks after onset. The skin test is less reliable than serologic tests to establish evidence of past infection.
Immunity is permanent after a single infection. Only one antigenic type exists. Passive immunity is transferred from mother to offspring; thus it is rare to see mumps in infants under age 6 months.
Gamma globulin is of no value for decreasing the incidence of Orchitis, even when given immediately after parotitis is first noted.
Mumps occurs throughout the world endemically throughout the year. Outbreaks occur where crowding favors dissemination of the virus. The disease reaches its highest incidence in children age 5-15 years, but epidemic occur in army camps. Although morbidity rates are high, the mortality rate is negligible, even when the nervous system is involved. Humans are the only known reservoirs of virus. The virus is transmitted by direct contact, airborne droplets, or formites contaminated with saliva and, perhaps urine. The period of communicability is from about 4 days before to about a week after the onset of symptoms. More intimate contact is necessary for the transmission of mumps than for measles or varicella.
About 30-40% of infections with mumps virus are in-apparent. Individuals with sub-clinical mumps acquire immunity. During the course of in-apparent infection, they can serve as sources of infection for others. Antibodies to mumps virus are transferred across the placenta and are gradually lost during the first year of life. In urban areas, antibodies are then acquired gradually, so that the 15-year-old group has about the same prevalence of persons with antibodies as the adult group. Antibodies are acquired at the same rate by persons living under favorable and unfavorable socio-economic conditions.
Mumps is usually a mild childhood disease. A live vaccine made in chick embryo cell culture is available. It produces a sub-clinical non-communicable infection. The vaccine is recommended for children over age 1 year and for adolescents and adults who have not had mumps parotitis, a single does of the vaccine given subcutaneously produces detectable in 95% of vaccines, and antibody persists for at least 8 years. Combination of live virus vaccines (measles-mumps-rubella) produces antibodies to each of the viruses in about 95%.