This disease is caused by a viral infection involving the BRAIN and SPINAL CORD. Since the development of effective vaccines in the 1950s (see IMMUNISATION), polio has been practically eliminated in most developed countries. Only 72 cases were reported in 2015 in Pakistan and Afghanistan.
Virus spreads by the stools-contaminated hands-mouth route and typically affects children. The anterior horn cells of the spinal cord, especially those in the lumbar region; the grey matter of the brain stem and cortex may be damaged.
The incubation period is around 7–14 days, the onset being marked by a mild fever and headache which improves after a few days. In around 85 per cent of infected children there is no further progression, but in some – after approximately one week – the symptoms recur, together with neck stiffness and signs of meningeal irritation (see MENINGES). Weakness of individual muscle groups is common, and may progress to widespread PARALYSIS. Involvement of the diaphragm and intercostal muscles may lead to respiratory failure and death unless artificial respiration is provided. Involvement of the cranial nerves and brain may lead to hoarseness and difficulty in swallowing, and CONVULSIONS may occur in young children.
This involves early bed rest, followed by PHYSIOTHERAPY and orthopaedic measures as required. At the onset of respiratory difficulties a TRACHEOSTOMY and artificial ventilation should be started. In cases of severe paralysis with persistent wasting of the limbs, surgery may be necessary to minimise the resulting disability.