Acute anterior poliomyelitis is a viral infection localized in the anterior horn cells of the spinal cord and certain brainstem motor nuclei. One of three types of poliomyelitis viruses is usually the cause of infection, but other members of the enteroviral group can cause a condition clinically and pathologically indistinguishable from poliomyelitis. Viral transmission is primarily fecal-oral, and initial invasion by the virus occurs through the gastrointestinal and respiratory tracts and spreads to the central nervous system through a hematogenous route. Although most individuals in an endemic area are infected with poliovirus, only 0.5% of infected individuals develop paralytic poliomyelitis.
