Rubella virus is a member of the Togaviridae family and produces the disease commonly known as German measles. Prior to the introduction of the vaccine, rubella was a common, mild disease with a rash. It was found worldwide and mostly affected children. It was uncommon in adults but had severe manifestations when affecting a pregnant woman during the first trimester because of the potential for birth defects. The structure of Rubellavirus is similar to other Togaviruses.
Humans are the only known reservoir for disease.
Transmission of the virus is via the respiratory route. Initial multiplication occurs in the respiratory tract. One week after infection, viremia occurs and this is later followed by the skin rash. The highest concentration of virus in the respiratory tract begins 3 days prior to the rash and lasts until 3 days after. If the virus infects a woman during the first 3-4 months of pregnancy, it may infect the placenta or fetus, multiply in any fetal organ and cause damage or death of certain cell types.