Etiology and Epidemiology

Mumps is caused by the mumps virus, a member of the genus Paramyxovirus of the family Paramyxo-viridae. Mumps virus has an irregular spherical shape averaging about 200 nanometers in diameter and contains a single-stranded RNA genome.

Mumps is a contagious disease, only slightly less contagious than rubella and measles, transmitted from infected persons to susceptible individuals by droplet spread and by direct contact with saliva. Mumps virus has also been shown to be transmitted across the placenta to the fetus. There is no natural reservoir for mumps other than human beings, which means that a continuous chain of susceptible contacts is necessary to sustain transmission. Although the period of communicability may be from 6 days before salivary gland symptoms to 9 days after wards, the period of greatest infectivity is about 48 hours before salivary gland involvement. There is no carrier state. Mumps has an incubation period from time of exposure to onset of salivary gland swelling of about 18 days with a range of 2 to 3 weeks.

In populated areas with no or low vaccination coverage, mumps is primarily an endemic disease of children, with epidemics occurring in closely associated groups such as schools. Its peak incidence is found in the age group 6 to 10 years, and mumps is rare before 2 years of age. Outbreaks may occur at intervals ranging from 2 to 7 years. There is a concentration of cases in the cooler seasons in temperate climates, and there is no apparent seasonality in tropical areas. In more remote isolated populations, mumps is not endemic, and disease depends upon introduction of the virus from the outside, at which time an epidemic may occur, affecting all age groups born since the previous epidemic. There is no evidence for a sex or racial difference in incidence of mumps, although clinically apparent mumps may be more common in males than in females.

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