Molecular epidemiology of rubella virus in Asia: utility for reduction in the burden of diseases due to congenital rubella syndrome.

BACKGROUND: Rubella is a mild disease mainly of infants, involving a rash and a fever. However, when women who have no immunity to rubella are infected during the early stage of pregnancy, their babies are often born with congenital rubella syndrome (CRS), which is characterized by a few disorders including deafness, cataracts and heart malformations. To prevent CRS, several strains of live attenuated rubella vaccine have been developed and introduced into immunization programs in many countries. In most Asian countries except Japan, Singapore and Taiwan, rubella remains uncontrolled, and the burden of diseases from CRS is high. In order to develop a control program to reduce the number of CRS cases in Asian countries, it is necessary to conduct a survey of rubella and CRS cases, and to then determine the genotype of the circulating rubella virus in each country.

METHODS: Cases of rubella and CRS, based on national reporting systems or active surveillance in the Asian countries, are summarized. Sequences of the E1 gene of the virus isolates from the Asian countries were compared by phylogenic analysis.

RESULTS: Recent studies of the molecular epidemiology of rubella virus worldwide revealed that there are two genotypes, and that genotype I is circulating almost worldwide, while genotype II is an Asian prototype restricted to the Asian continent. Genotype I viruses fall into a number of groups, some of which are geographically localized. Antigenically these two genotypes are cross-reactive and immunization with either virus results in immunity to all rubella viruses.

DISCUSSION: The hypotheses that rubella virus has evolved on the Asian continent is proposed. The World Health Organization (WHO) has recognized that a rubella immunization program can be combined with the measles immunization program. Inclusion of rubella in the expanded program of immunization (EPI) of measles would be ideal in Asian countries, as it would be efficient and cost effective to administer one injection containing a three-combined vaccine (MMR). It would also be desirable given that WHO require laboratory tests to confirm the presence of measles or rubella as part of it's measles control project, because rubella is often misdiagnosed as measles.