Further cleavage events are carried out by 3C - the main picornavirus protease. Note the icosahedral symmetry which is clearly visible in this image. As with all the Enteroviruses, they are transmitted by the faecal-oral route. Virus production at this site leads to a transient viraemia , following which the virus may infect the CNS . Replication of the virus in the CNS occurs in the 'grey matter', particularly motor neurons in the anterior horns of the spinal cord and brain stem.
Death is usually due to respiratory failure by paralysis of the intercostal muscles and diaphragm.
In 1988, the World Health Assembly established the year 2000 for achieving global poliomyelitis eradication. By 1994, the Americas were certified as polio-free. All other regions are making steady progress towards this goal. The WHO reports that global eradication of poliomyelitis is still on course for the year 2000. Many types grow very poorly in vitro.