Cosavirus A is a species of the genus Cosavirus within the family Picornaviridae. Cosaviruses are non‑enveloped positive‑sense RNA viruses first identified in 2008 in fecal samples from South Asian children with non‑poliomyelitis acute flaccid paralysis. Cosavirus A has been detected worldwide in stool and sewage samples, but its clinical significance remains unclear.
Explanation
Cosavirus virions are non‑enveloped, spherical particles about 30 nm in diameter with a pseudo‑T=3 icosahedral capsid composed of 60 protomers. The monopartite linear genome is 7‑8 kilobases of positive‑sense RNA with a poly(A) tail and a viral protein VPg linked to the 5′ end. The genome encodes a single polyprotein that is processed into structural and non‑structural proteins; the P1 region forms the capsid proteins VP1, VP2, VP3 and VP4 while the P2 and P3 regions encode replication enzymes. Cosavirus replication is cytoplasmic: the virion binds a host receptor, undergoes endocytosis and uncoating, and the genome is translated via an internal ribosome entry site to produce polyprotein precursors. New virions assemble in membrane‑associated replication complexes and are released by cell lysis. In epidemiologic studies, human cosavirus RNA has been detected at high prevalence in feces of children from Pakistan, where 44 % of healthy and 49 % of paralyzed children tested positive. Subsequent surveys in Nigeria and Tunisia found prevalence rates around 32–40 %. Cosaviruses have also been found in sewage and in stool of adults with and without diarrhea. Despite this high detection rate, no consistent association with disease has been demonstrated; prevalence is similar in symptomatic and asymptomatic individuals. Five species (A–E) have been proposed based on sequence identity, and a sixth species F has been suggested. Cosaviruses are most closely related to cardioviruses and senecavirus.
Discovery and Distribution
Cosavirus A was first detected during investigations of non‑polio acute flaccid paralysis in Pakistan in 2008. Since then, human cosaviruses have been detected in countries across Africa, Asia and Europe, often in wastewater and environmental samples. Prevalence studies highlight high infection rates in children, but there is little evidence that these viruses cause illness. The genetic diversity of cosaviruses has prompted classification into multiple species, and recombination events have been documented. The absence of disease association suggests these viruses might form part of the normal enteric virome. Cosavirus A exemplifies a recently recognized genus of picornaviruses that commonly infects humans but has no established pathogenicity. Its small non‑enveloped RNA virion and polyprotein genome mirror the basic design of other Picornaviridae members. Continued surveillance will clarify whether cosaviruses contribute to disease or simply reflect background viral flora. Related Terms: Picornaviridae, Cardiovirus, Senecavirus, Cosavirus B, Salivirus A