<unk>  is a small, nonenveloped, positive stranded RNA virus, that belongs to the family of Picornaviridae.  It is a transient inhabitant of the GI tract, where it replicates, to further infect distant regions, however,<unk>  rarely causes symptoms.  Three serotypes of<unk> , P1, P2 and P3, may be identified.  Tissue tropism is dictated by extracellular and intracellular factors. The cellular receptor CD155 is the extracellular receptor for<unk> .  It may be identified in organs, such as the brain, heart, skeletal muscle and liver.  Intracellular factors that influence viral replication include: polypyrimidine tract binding protein (PTB), which binds to IRES; the proteolytic processing of<unk>  proteins; and lack of an host factor for viral replication. Humans are the only natural reservoirs for<unk> .
Poliovirus
Echovirus
Ophiovirus
Arbovirus
Erbovirus
Enterovirus
Parechovirus
Varicosavirus