picornavirus

Picornaviruses are a large family of small, non-enveloped, positive-sense RNA viruses with icosahedral capsids. The name derives from pico, meaning small, and RNA. The genome is a single, linear RNA of about 7.2 to 8.5 kilobases and contains one long open reading frame that encodes a polyprotein. This polyprotein is proteolytically processed into structural proteins VP4, VP2, VP3, and VP1 that form the capsid, and nonstructural proteins including the proteases 2A and 3C and the RNA-dependent RNA polymerase 3Dpol. The genome features a 5' untranslated region with an internal ribosome entry site (IRES) that drives cap-independent translation, and a 3' untranslated region with a poly(A) tail.

Replication occurs in the cytoplasm after the virus binds to cellular receptors and enters the cell. The nonenveloped virion makes the family relatively resistant to environmental stress, supporting transmission by fecal-oral routes for many enteroviruses and by respiratory spread for rhinoviruses. The family includes several well-known genera: Enterovirus (which includes poliovirus, coxsackieviruses, and echoviruses), Rhinovirus (common cold viruses), Hepatovirus (hepatitis A virus), and other genera such as Aphthovirus, Parechovirus, and Kobuvirus.

Clinical manifestations range from mild respiratory or gastrointestinal illness to severe disease such as poliomyelitis or aseptic meningitis, depending on the virus and host factors. Diagnosis is typically by RT-PCR or serology. Vaccines exist for poliovirus and hepatitis A; most picornaviruses do not have licensed vaccines. Antiviral options are limited, with clinical management largely supportive. Picornaviruses have a substantial global health impact, reinforcing the importance of surveillance and vaccine programs for targeted members.