alphavirus

Alphavirus is a genus of enveloped, positive-sense single-stranded RNA viruses in the family Togaviridae. The genome is about 11.7 kilobases in length and features two major coding regions: a 5' region that encodes nonstructural proteins (nsP1–nsP4) necessary for RNA synthesis, and a 3' region that gives rise to a structural polyprotein (C–E3–E2–6K–E1) via a subgenomic RNA. After infection, replication occurs in the cytoplasm on membrane structures derived from host cell organelles, forming replication complexes and producing subgenomic RNA for structural protein expression.

Transmission is typically via arthropod vectors, especially mosquitoes such as Aedes and Culex species. Alphaviruses often maintain enzootic cycles involving birds, rodents, or other small mammals, with spillover into humans and other animals through vector feeding. The clinical presentation in humans ranges from febrile illness with rash to severe arthralgia and, in some lineages, encephalitis. Neurological disease is more common with certain species.

Notable alphaviruses include the chikungunya virus, which causes fever and severe joint pain; eastern, western, and Venezuelan equine encephalitis viruses, which can cause encephalitis with higher mortality in some outbreaks; Sindbis and Mayaro viruses, associated with febrile and rash illnesses in various regions. Alphaviruses are distributed worldwide, with human disease largely linked to vector exposure and local ecology.

Diagnostics rely on molecular methods (RT-PCR) and serology to detect viral RNA or specific antibodies. Treatment is primarily supportive, with no broadly approved antiviral therapy. Prevention focuses on vector control and personal protection against mosquito bites; vaccines for humans are not widely licensed, though research and some veterinary vaccines exist.