Human echovirus 9

Echovirus 9 (also known as E-9, E.C.H.O. 9, and formerly Coxsackie A23 or A23 virus)^[1] is a serotype of echovirus. When first discovered, it was labelled as a coxsackie A virus, A23. It was later discovered that A23 was an echovirus antigenically identical to the already-known echovirus 9.^[2]

Echovirus 9
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdom:	Orthornavirae
Phylum:	Pisuviricota
Class:	Pisoniviricetes
Order:	Picornavirales
Family:	Picornaviridae
Genus:	Enterovirus
Species:	Enterovirus B
Strain:	Echovirus 9
Synonyms
E-9 A23 virus Coxsackie A23

Echovirus 9 is the most common enterovirus type.^[3] It is a common cause of illness in humans, although unlike many enteroviruses, it rarely infects infants.^[3] Its transmission is facilitated by crowded conditions. Those who are slightly ill and children are at particular risk of contracting echovirus 9 (A23).^[4]