Alphaviruses

Alphaviruses are a genus of positive-sense, single‑stranded RNA viruses in the family Togaviridae. They are enveloped, roughly 70 nm in diameter, and possess a genome of about 11–12 kilobases that encodes non‑structural proteins required for replication and structural proteins that form the capsid and envelope glycoproteins. The viral envelope contains E1 and E2 glycoproteins that mediate attachment to host cell receptors and membrane fusion. Alphaviruses are phylogenetically divided into several subgroups, including the Old World group (e.g., chikungunya virus, Sindbis virus) and the New World group (e.g., Eastern, Western, and Venezuelan equine encephalitis viruses).

These viruses are arthropod‑borne, primarily transmitted by mosquitoes, and maintain enzootic cycles involving vertebrate hosts such as birds, rodents, and equids. Human infection occurs through mosquito bites and can lead to a spectrum of clinical manifestations. Old World alphaviruses commonly cause febrile illness with arthralgia and rash, whereas New World alphaviruses are neurotropic, producing encephalitis that may be severe, especially in children and the elderly. The incubation period ranges from 2 to 14 days, and most infections are self‑limiting, though severe cases may require supportive care.

Diagnosis relies on serologic testing for virus‑specific IgM antibodies, reverse transcription polymerase chain reaction, or virus isolation from blood or cerebrospinal fluid. No specific antivirals are widely approved; treatment is mainly symptomatic. Prevention focuses on vector control, personal protective measures against mosquito bites, and, for certain viruses such as Venezuelan equine encephalitis, vaccination of at‑risk animal populations. Ongoing research aims to develop broad‑spectrum antivirals and improved vaccines for alphavirus infections.