Togaviridae

Togaviridae is a family of enveloped, positive-sense single-stranded RNA viruses with an icosahedral nucleocapsid. Members replicate in the cytoplasm and have genomes of approximately 9.7 to 12 kilobases that are capped at the 5' end and polyadenylated at the 3' end. The name derives from the Latin toga-like envelope structure observed in some virions.

Taxonomy and notable members: The family contains two genera, Alphavirus and Rubivirus. Alphaviruses include pathogens such as chikungunya virus, Eastern and Western equine encephalitis viruses, and Mayaro virus, which are typically transmitted by mosquitoes or other arthropods. Rubiviruses include the rubella virus, which causes rubella in humans.

Virion structure and genome organization: Alphaviruses are enveloped and possess glycoprotein spikes on their envelope formed by the E1 and E2 proteins; the genome is nonsegmented RNA that encodes nonstructural proteins (nsP1–nsP4) involved in replication, and a structural polyprotein produced from a subgenomic RNA that encodes the capsid and the envelope glycoproteins. Rubiviruses have a single open reading frame that is translated into a polyprotein and processed into both nonstructural and structural proteins. Both genera produce virions that are adapted for assembly at the host cell membrane.

Replication and life cycle: Entry occurs via receptor-mediated endocytosis and pH-triggered fusion in endosomes. Translation of the genome yields replication complexes that synthesize negative-strand intermediates, from which genomic and subgenomic RNAs are produced. New virions bud from the plasma membrane.

Clinical and public health aspects: Alphavirus infections range from febrile illness with rash and arthralgia to severe encephalitis in some cases, depending on the virus. Rubella infection, particularly during pregnancy, can cause congenital rubella syndrome. Vaccination against rubella is common in many regions; vaccines or other measures to control alphavirus outbreaks rely on public health interventions and vector control.