Rubella Virus

Abstract

Rubella virus is a human virus belonging to the family Togaviridae and the sole member of the rubivirus genus. Rubella virus has a small genome composed of single‐stranded RNA and produces only five proteins. The rubella virus replication cycle takes place entirely within the cytoplasm of the infected cell. Rubella virus establishes a body‐wide or systemic infection that is manifested by mild symptoms including rash, lymph node swelling and low‐grade fever. However, rubella virus is an important human pathogen because it causes a spectrum of serious birth defects known collectively as congenital rubella syndrome (CRS) when a mother lacking immunity is infected during the first trimester of pregnancy. CRS can include blindness, deafness, mental retardation, heart malformations and endocrine dysfunctions. Before development of effective live, attenuated vaccines, rubella virus was the leading teratogenic agent of an infectious nature. Through use of these vaccines, rubella and CRS are controlled in much, but not all, of the world and are targeted for elimination in the Western Hemisphere and Europe. Key Concepts: Rubella virus causes a benign systemic illness characterised by a rash, but is a dangerous teratogen when infection occurs during pregnancy. Fetal infection by rubella virus results in congenital rubella syndrome, a constellation of serious birth defects, particularly deafness, blindness and mental retardation. Rubella virus is classified in the Togaviridae family and is the only member of the rubivirus genus. Rubella virions are pleiomorphic, approximately 70 nm in diameter and consist of a quasispherical capsid containing the genome RNA surrounded by an envelope composed of a lipid bilayer from which protrude glycoprotein spikes. The rubella virus genome is a plus‐polarity RNA, 10 000 nucleotides in length, which encodes only five proteins: P150 and P90, both of which participate in RNA replication in the infected cells, and capsid (C) and envelope glycoproteins 1 and 2 (E1 and E2) which comprise the virion. In the infected cell, rubella virus replication takes place entirely within the cytoplasm. In the infected cell, rubella virus RNA replication, which proceeds through an RNA intermediate, takes place in association with cell membranes. In the infected cell, rubella virion formation takes place in association with the Golgi apparatus and virions are released by exocytosis. Rubella virus isolates worldwide cluster into 13 genotypes that fit into two distinct clades with an overall diversity at the nucleotide level of approximately 10%, a very low level for an RNA virus. Live, attenuated rubella virus vaccines, available since approximately 1970, have been used successfully to control or eliminate rubella in developed countries whereas implementation of these vaccines is progressing, but not complete, in undeveloped countries of the world.