Rubella Virus: Molecular Composition, Pathogenesis, Diagnosis, And Control

Publisher Summary Rubella virus (RV) is a member of the genus rubivirus in the family of togaviridae. It is a spherical particle of about 60-70nm in diameter. The particle is enveloped with a single-stranded polyadenylated genomic RNA of positive polarity composed of 9757 nucleotides in length, excluding the poly (A) tail and has a very high G/C content of 69.5%. The virus is encapsulated by a capsid protein (C) and is contained within a lipid bilayer envelope (E), in which the two virus-specific envelope proteins, E1 and E2, are embedded. Phylogenetic analysis of a collection of over 100 gene sequences from viruses isolated from several countries between 1961 and 2000 verified the existence of at least two main genotypes: rubella genotype I (RGI) isolates from Japan and the Western Hemisphere, and rubella genotype II (RG II) that showed greater genetic diversity than did RG I. RG II viruses are limited to Asia. Of interest, is that RG I viruses are also present in most of the countries where RG II viruses are isolated. Antigenically, RG I and II are cross reactive and immunization with either virus results in immunity to all rubella viruses. Diagnosis involved hemagglutination inhibition (HAI) that was the first serological assay to be used in clinical laboratories and remained for some time the standard, against which many of the newer assays were compared. The HAI assay is no longer required when screening for protective maternal immunity. During the past 15 years, the HAI assay has been replaced entirely by more sensitive, specific, and technically less demanding enzyme-linked immunosorbent assay (ELISA) and microparticle enzyme immunoassay (MEIA) also several strains of live-attenuated rubella vaccines have been developed and introduced into immunization programs in many industrialized countries.