Mumps is an illness characterized by acute-onset unilateral or bilateral tender, self-limited swelling of the parotid or other salivary gland(s) that lasts at least 2 days and has no other apparent cause.
Mumps is caused by a paramyxovirus with a negative-strand, nonsegmented RNA genome of 15,384 bases encoding at least 8 proteins: the nucleo- (N), phospho- (P), V, matrix (M), fusion (F), small hydrophobic (SH), hemagglutinin–neuraminidase (HN), and large (L) proteins. The N, P, and L proteins together provide the polymerase activity responsible for genome transcription and replication. The viral genome is surrounded by a host cell–derived lipid bilayer envelope containing the M, F, SH, and HN proteins. The M protein is involved in viral assembly, whereas the HN and F proteins are responsible for cell attachment and entry and are the major targets of virus-neutralizing antibody. The V and SH proteins are accessory proteins, acting as antagonists of the host antiviral response; the former interferes with the interferon response and the latter with the tumor necrosis factor α (TNF-α)–mediated apoptotic signaling pathway. Because of the hypervariability of the SH gene, its nucleotide sequence is used to genotype the virus for molecular epidemiologic purposes. Thus far, 12 mumps virus genotypes have been assigned by SH gene sequence and are designated A–N (with the exclusion of E and M, which have been merged with genotypes C and K, respectively).
Nucleotide sequencing of clinical isolates shows that virus genotypes D and G circulate predominantly in the Western Hemisphere; genotypes F, C, and I in the Asia–Pacific region; and genotypes B, H, J, and K in the Southern Hemisphere (Fig. 202-1). Although numerous mumps virus genotypes have been identified and some vary antigenically from others, only one serotype exists, and there is no evidence to suggest that certain circulating virus strains are more virulent or contagious than others.
Distribution of reported mumps genotypes, 2005–2016. Pie-slice size represents the frequency of the reported genotype. (Figure courtesy of WHO, with permission. This figure has been updated by the author to include data on mumps virus genotypes reported since 2012.)
Mumps is endemic worldwide, with epidemics every 3–5 years in unvaccinated populations. These epidemics typically occur in locations where children and young adults congregate, such as schools, military barracks, and other institutions. In countries without national mumps vaccination programs, the estimated annual global incidence is 100–1000 cases per 100,000 population. After the introduction of mumps vaccine in the United States in 1967, the number of reported cases declined dramatically. Within a few years of the 1977 recommendation by the Advisory Committee on Immunization Practices (ACIP) for use of mumps-containing vaccine (measles–mumps–rubella; MMR) in the national immunization schedule, the number of reported cases declined by >97%. In the years ...