Rubella (German measles) is caused by the rubella virus, which is an RNA virus in the Togaviridae family. Transmission is through the respiratory route. Its incubation period is 14-21 days. A prodrome of irritability, malaise, mild conjunctivitis, headache, fever, adenopathy, and minimal respiratory symptoms may appear 1-7 days prior to the cutaneous eruption. An exanthematous eruption starting on the face and spreading caudally then typically appears. This rash may be absent in as many as 25% of cases.
Infection in the United States is rare, owing to widespread vaccination. There is a higher incidence in confined populations such as military bases and schools. The disease is more common in the spring and summer. Arthralgias and mild arthritis, splenomegaly, thrombocytopenia, and testicular pain are sometimes seen. Encephalitis occurs in 1 out of 6000 cases. Pain on lateral or upward eye movement is common in this disorder. Thrombocytopenic purpura is also a rare complication.
Even in the immunocompromised host, rubella is usually a benign illness. The major impact of rubella is on the fetus of a pregnant patient and is one of the TORCH (toxoplasmosis, other [syphilis, varicella zoster, parvovirus B19], rubella, cytomegalovirus, and herpes simplex) diseases. These disorders can cause fetal heart and eye malformations, cataracts, deafness, retardation, thrombocytopenic purpura, hepatosplenomegaly, intrauterine growth retardation, interstitial pneumonia, myocarditis, myocardial necrosis, and metaphyseal bone lesions.