Rubella virus (RuV) is the pathogenic agent of the disease rubella, transmitted only between humans via the respiratory route, and is the main cause of congenital rubella syndrome when infection occurs during the first weeks of pregnancy. Rubella virus, scientific name Rubivirus rubellae, is a member of the genus Rubivirus and belongs to the family of Matonaviridae, whose members commonly have a genome of single-stranded RNA of positive polarity which is enclosed by an icosahedral capsid. the molecular basis for the causation of congenital rubella syndrome was not yet completely clear, but in vitro studies with cell lines showed that rubella virus has an apoptotic effect on certain cell types. There is evidence for a p53-dependent mechanism. Taxonomy Rubella virus (Rubivirus rubellae) is assigned to the Rubivirus genus. Matonaviridae family Until 2018, Rubiviruses were classified as part of the family Togaviridae, but have since been changed to be the sole genus of the family Matonaviridae. This family is named after George de Maton, who in 1814 first distinguished rubella from measles and scarlet fever. The change was made by the International Committee on the Taxonomy of Viruses (ICTV), the central governing body for viral classification. Matonaviridae remains part of the realm that it was already in as Togaviridae, Riboviria, because of its RNA genome and RNA dependent RNA polymerase. Other rubiviruses In 2020, Ruhugu virus and Rustrela virus joined Rubella virus as second and third of only three members of the genus Rubivirus. Neither of them are known to infect people. Morphology While alphavirus virions are spherical and contain an icosahedral nucleocapsid, RuV virions are pleiomorphic and do not contain icosahedral nucleocapsids. Phylogeny ICTV analyzed the sequence of RuV and compared its phylogeny to that of togaviruses. They concluded:Phylogenetic analysis of the RNA-dependent RNA polymerase of alphaviruses, rubella virus and other positive-sense RNA viruses shows the two genera within the Togaviridae are not monophyletic. In particular, rubella virus groups more closely with members of the families Benyviridae, Hepeviridae and Alphatetraviridae, along with several unclassified viruses, than it does with members of the family Togaviridae belonging to the genus Alphavirus. Structure The spherical virus particles (virions) of Matonaviridae have a diameter of 50 to 70 nm and are covered by a lipid membrane (viral envelope), derived from the host cell membrane. There are prominent "spikes" (projections) of 6 nm composed of the viral envelope proteins E1 and E2 embedded in the