<unk>  9 (also known as E-9, E.C.H.O. 9, and formerly Coxsackie A23 or A23 virus) is a serotype of<unk> . When first discovered, it was labelled as a coxsackie A virus, A23. It was later discovered that A23 was an<unk>  antigenically identical to the already-known<unk>  9.<unk>  9 is the most common enterovirus type. It is a common cause of illness in humans, although unlike many enteroviruses, it rarely infects infants. Its transmission is facilitated by crowded conditions. Those who are slightly ill and children are at particular risk of contracting<unk>  9 (A23).
Human echovirus 9
Dhori virus
Human coronavirus HKU1
Human coronavirus OC43
Human bocavirus
Human coronavirus 229E
Hendra virus
Human coronavirus NL63