picornaviruses

Picornaviruses are a family of small, non-enveloped, single-stranded positive-sense RNA viruses belonging to the order Picornavirales. The family Picornaviridae includes genera such as Enterovirus, Rhinovirus, Aphthovirus, Hepatovirus, Cardiovirus, and Parechovirus. They share a genome of about 7.2 to 8.5 kb and an icosahedral capsid composed of four structural proteins (VP1–VP4).

Their genome has a single open reading frame that encodes a polyprotein, which is proteolytically cleaved into structural and nonstructural proteins. The 5' end carries a protein primer (VPg), and the 3' end has a poly(A) tail. Translation uses an internal ribosome entry site (IRES) to initiate synthesis of the polyprotein, which is processed by viral proteases such as 2A and 3C.

Replication occurs in the cytoplasm. The RNA-dependent RNA polymerase 3Dpol copies the genome within replication complexes associated with cellular membranes. New virions assemble in the cytoplasm and are released by cell lysis or exocytosis.

Most picornaviruses are transmitted by the fecal-oral route or via respiratory droplets. Rhinoviruses are commonly spread by the respiratory route, while enteroviruses and hepatitis A virus are typically transmitted fecal-oral. Clinically, picornaviruses cause a wide range of diseases from mild colds caused by rhinoviruses to more serious illnesses such as poliomyelitis (poliovirus), aseptic meningitis, myocarditis, and hand-foot-and-mouth disease (enteroviruses and coxsackieviruses), as well as hepatitis A.

Control is limited to vaccination for poliovirus and general public health measures; no universal vaccine exists for most picornaviruses. Management is mainly supportive, with ongoing antiviral research.