The virus

Rubella virus is a single-stranded RNA virus, which is the only member of the genus Rubivirus within the family Togaviridae. The outer envelope protein E1 is the viral haemagglutinin protein responsible for binding to the cell receptors to initiate infection.

Epidemiology

Prevalence

Rubella has a worldwide prevalence. Before the introduction of vaccination, it circulated in epidemic form with an epidemic cycle every 6–8 years. In countries with effective childhood rubella vaccination programmes this pattern has been interrupted, as has been the number of reports of endemic cases. In countries without vaccination programmes it remains an infection of childhood. About 15–20% of young adults remain susceptible, putting them (especially pregnant women) at risk of acute infection as the virus is endemic and continues to circulate in the community.

Route of spread

Infection is spread via respiratory secretion droplets. The virus is highly infectious with attack rates of 50–80% in susceptible individuals in communities during outbreaks.

Incubation period

The rash usually develops 16–18 days after exposure, but the incubation period may range from 14–21 days. Infection is first initiated in the respiratory epithelium and then spreads and replicates in the regional lymph node. This is then followed by viraemia and dissemination of the virus to multiple sites.

Infectious period

Maximum viral shedding from the respiratory tract of infected individuals occurs from 5 days before to 7 days after the appearance of the rash.