Because of widespread vaccination efforts, its role as a major cause of childhood morbidity has greatly diminished.
Humans are the only natural host.
Infection is uncommon under the age of 1 year, and congenital infection is rare but can lead to fetal loss in the first trimester. Virus is shed in saliva from as long as 6 days before to 5 days after clinical onset. Initial replication occurs in the pharynx, followed by viremic dissemination. Both humoral and cell-mediated immune responses are induced and correlate with cessation of viremia and salivary virus excretion. Two thirds of cases are symptomatic, with initial symptoms of malaise and fever predominating.