Picornaviridae

Picornaviridae is a family of small, non-enveloped, icosahedral RNA viruses in the order Picornavirales. Virions are roughly 22–30 nanometers in diameter and carry a positive-sense, single-stranded RNA genome. The family comprises multiple genera, including Enterovirus, Rhinovirus, Hepatovirus, Aphthovirus, Cardiovirus, Parechovirus and Kobuvirus, which collectively infect a wide range of humans and animals.

The genome is a single, large open reading frame that encodes a polyprotein processed by viral proteases into structural and non-structural proteins. In the P1 region, the structural proteins VP4, VP2, VP3 and VP1 form the virion, while P2 and P3 encode non-structural proteins involved in replication and proteolysis. A covalently attached VPg protein links the genome to the 5' end, and translation is driven by an internal ribosome entry site (IRES) within the 5' untranslated region. The 3' end contains a polyadenylated tail. Replication occurs in the cytoplasm, with the polyprotein cleaved by viral proteases (such as 2A and 3Cpro) to generate functional components. The RNA polymerase 3Dpol synthesizes negative-sense intermediates and progeny genomes, which assemble into new virions and are released from the cell.

Clinical and veterinary relevance varies by genus. Rhinoviruses cause common colds; enteroviruses include poliovirus and Coxsackie/Echoviruses; Hepatovirus includes hepatitis A virus; Aphthoviruses include foot-and-mouth disease virus in livestock. Transmission is typically fecal-oral or respiratory, and many members are highly contagious. The family is notable for its reliance on IRES-mediated translation and its extensive genetic diversity and recombination.