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Rubella (German Measles)
Definition
Although most cases of rubella infection lead to a mild viral illness, significant morbidity occurs when rubella virus infects the fetus, particularly during the first trimester of pregnancy, when it causes miscarriage and the congenital rubella syndrome in up to 90% of cases. Humans are the only known host, so this disease is eradicable.
The Pathogen
Rubella is a single-stranded, positive-sense RNA virus that is a member of the Togaviridae family, in the Rubivirus genus. The virus has a diameter of about 60 nm and includes a core protein and two envelope proteins.
Epidemiology
Rubella virus is spread person to person via the respiratory route, with lifelong immunity after infection. Prior to the availability of live attenuated rubella vaccine, rubella infection was nearly ubiquitous among children, occurring in the spring season and in large epidemics every 3 to 8 years. In the prevaccine era, up to 4 infants out of every 1000 live births worldwide were born with congenital rubella syndrome, and the incidence of congenital rubella syndrome was between 0.1 to 0.2 per 1000 live births during endemic phases and 0.8–4.0 during epidemics. With widespread use of the vaccine, the number of cases has been dramatically reduced. Rubella was eliminated in the United States in 2004 and in the Americas since 2015. In the United States, fewer than 10 cases occur per year among individuals infected outside of the country. Unfortunately, global plans to eliminate rubella in 5 of 6 World Health Organization regions by 2020 failed, and about 50% of babies worldwide do not have access to rubella-containing vaccines. Rubella outbreaks have continued to occur related to partial vaccination strategies, lack of political commitment, disruption due to war and conflict, and the costs of elimination programs. Herd immunity thresholds, which have varied by geographic region, have generally ranged from 70 to 90%, given a basic reproductive rate that is estimated to be 3 to 8 in Western settings but as high as 12 in crowded developing settings.
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