viral disease that runs a mild and benign course in most people. Although rubella is not usually a serious illness in children or adults, it can cause birth defects (congenital disorder) or the loss of a fetus if a mother in the early stages of pregnancy becomes infected.

German physician Daniel Sennert first described the disease in 1619, calling it röteln, or rubella, for the red-coloured rash that accompanies the illness. Rubella was distinguished from a more serious infectious disease, measles, or rubeola, in the early 19th century. It came to be called German measles in the latter part of the 19th century when the disease was closely studied by German physicians. The rubella virus was first isolated in 1962, and a vaccine was made available in 1969. Rubella occurred worldwide before immunization programs were instituted, with minor epidemics (epidemic) arising every 6 to 9 years and major epidemics every 30 years. Because of its mildness it was not considered a dangerous illness until 1941, when Australian ophthalmologist N. McAlister Gregg discovered that prenatal infection with the virus was responsible for congenital malformations in children.

The rubella virus is spread through the respiratory route, being shed in droplets of respiratory secretions from an infected person. The incubation period is 12 to 19 days, with most cases occurring about 15 days after exposure. The first symptoms to appear are a sore throat and fever, followed by swollen glands and a rash that lasts about three days. Infected individuals tend to be most contagious when a rash is erupting. The duration and severity of the illness are variable and complications are rare, although encephalitis may follow. As many as 30 percent of infections are thought to occur without symptoms. Once infected, a person develops lifelong immunity to rubella.

Fetal infection occurs when the virus enters the placenta from the maternal bloodstream. Defects of the eye, heart, brain, and large arteries are most common and, together, are referred to as congenital rubella syndrome. The risk to the fetus is greatly reduced if the mother is infected after 20 weeks' gestation. If a woman of childbearing age has not had a natural infection with rubella virus, she should be immunized prior to pregnancy.