Poliovirus is a small virus that lacks a viral envelope but has a capsid that surround its, single-stranded, positive-sense RNA are transmitted by food but virulent strains of this agent are now extremely rare. Poliovirus is an error-prone enteric virus spread by the fecal-oral route, and rarely invades the central nervous system (CNS). However, in the rare instances when poliovirus invades the CNS, the resulting damage to motor neurons is striking and often permanent.