2008; Weibel et al., 1967). In the United States, mumps vaccines are manufactured using the Jeryl Lynn strain mumps virus that was isolated from the throat of Jeryl Lynn Hilleman in the 1960s (Plotkin and Rubin, 2008). The vaccine is currently licensed in the mono-, tri-, and tetravalent forms, although the monovalent, Mumpsvax (Merck and Co., Inc.), is no longer available in the United States.

Prior to the licensing of a live-attenuated mumps vaccine, mumps outbreaks occurred every 2 to 5 years, with peak incidence from January through May (Anderson and Seward, 2008; Litman and Baum, 2010). Since the introduction of the vaccine, the incidence of mumps infection has been reduced greatly, evidenced by a 99 percent decrease in mumps infection from 1968 to 1995 (CDC, 1998).

Rubella

Rubella, also known as German measles, is caused by an enveloped, positive-sense RNA togavirus of the genus Rubivirus (Gershon, 2010b). The rubella virus genome consists of approximately 9,800 nucleotides, and the virus can be divided into two clades and at least seven genotypes (Zheng et al., 2003). Maturing by budding from the cell membrane (Murphy et al., 1968), rubella virus is relatively unstable and vulnerable to chemical inactivation, extremes of pH and heat, lipid solvents, and ultraviolent light (Gershon, 2010b).

Rubella is spread through contact with infectious respiratory secretions, and replication occurs in the nasopharynx of the infected individual (Plotkin and Reef, 2008). Rubella infections are subclinical in 25 to 50 percent of cases (CDC, 1998). In those cases in which clinical illness develops, the beginning of the 12- to 23-day incubation period is largely asymptomatic (CDC, 1998; Plotkin and Reef, 2008). By the end of the second week virus can be isolated from the blood and symptoms of conjunctivitis, low-grade fever, lymphadenopathy, and malaise are present (Plotkin and Reef, 2008). A rash follows spreading downwards from the face before fading within 1 to 3 days (Plotkin and Reef, 2008). Rubella illness in a child or adult is usually benign although arthritis and arthralgia has been observed in association with viral replication in the synovial cavity of the joints (Plotkin and Reef, 2008). Other complications of rubella include encephalitis, Guillain-Barré syndrome (GBS), progressive rubella panencephalitis, and thrombocytopenia (Gershon, 2010b; Plotkin and Reef, 2008).

Rubella virus infection during pregnancy can lead to congenital rubella infection in neonates. The disease outcome is directly correlated to the age of the fetus at the time of infection with younger fetuses experiencing more severe disease (Gershon, 2010b). Infections within the first 2 months of pregnancy can cause multiple congenital defects or spontaneous abortion in



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