Type Species

Rubella virus

(RUBV)

Distinguishing Features

The genome is 9,757 nts in size exclusive of the 3 terminal poly (A) tract (S_20W of 40S). The order of the genes in the nonstructural protein ORF is NH₂-P150-P90-COOH. The nonstructural protein precursor is cleaved by a papain-like cysteine protease located near the C-terminus of P150. The virion has a capsid protein (CP, 34 10³) and two envelope glycoproteins (E1, 59 10³; E2, 44-50 10³), but no equivalent of E3 or the 6K protein of the alphaviruses. The order of the proteins in the structural polyprotein precursor is NH₂-CP-E2-E1-COOH. The two cleavages that separate these three structural proteins are effected by signal peptidase (the E2 signal sequence remains attached to CP). Carbohydrates make up 10% of the mass of E1 and 30-40% of E2. E2 is heterogeneous in size due to differential processing of glycans (N- and O-linked). Rubella virus (RUBV) is transmitted by aerosol. The illness, rubella or German measles, is generally benign in nature, but complications such as arthritis, thrombocytopenia purpura, and encephalitis can occur. Congenital transmission is the most serious consequence of rubella as viral infection of the foetus during the first trimester of pregnancy leads to a constellation of serious birth defects known as rubella congenital syndrome (CRS). CRS infants shed virus for up to six months. CRS patients suffer a variety of autoimmune and psychiatric disorders in later life, including a fatal neurodegenerative disease known as progressive rubella panencephalitis (which has also been described in post-natally infected individuals). RUBV is endemic worldwide, although it is controlled by vaccination in most developed countries. Only one serotype has been described, although two genotypes have been detected.

List of Species Demarcation Criteria in the Genus

Not applicable.

List of Species in the Genus

Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus name, genome sequence accession numbers [ ], and assigned abbreviation ( ) are:

Species in the Genus

Rubella virus

[M15240, X05259, X72393, L78917]

(RUBV)

Tentative Species in the Genus

None reported.

List of Unassigned Viruses in the Family

None reported.

Phylogenetic Relationships within the Family

Amino acid sequence homology between RUBV and alphaviruses has been detected only within the nonstructural proteins (see Fig. 2). Nucleotide and amino acid sequence homology has been demonstrated among all alphaviruses sequenced, and phylogenetic relationships have been estimated using the nsP1, nsP4 and E1 genes. The seven antigenic complexes (see above) are supported as distinct monophyletic groups by these analyses (Fig. 4).

Similarity with Other Taxa

Togavirus nonstructural proteins (alphavirus nsP1, nsP2, and nsP4 and the methyl transferase, helicase and replicase regions of RUBV) share some sequence homology with the nonstructural proteins of Hepatitis E virus (Caliciviridae) and several groups of plant viruses, including tobamoviruses, bromoviruses and tobraviruses, suggesting a common origin for the replicases of these viruses. Differences in genome organization and segmentation presumably reflect extensive recombination and modular evolution.

Derivation of Names

Alpha: from Greek letter .

Rubi: from Latin rubeus “reddish”.

Toga: from Latin toga “cloak”.