Apr 6, 2014
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Once known as infantile paralysis, 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. People who have not been fully vaccinated, however, may get the disease: it remains a serious risk for unvaccinated travellers to Africa, Asia or southern Europe. Most reported cases are now from sub-Saharan Africa.

Pathology There are three types of virus, infection spreading by the stools-contaminated hands-mouth route. Children are most susceptible.

One attack usually produces permanent immunity, and second attacks are rare. The virus typically affects the anterior horn cells of the spinal cord, especially those in the lumbar region; the grey matter of the brain stem and cortex may also be damaged.

Vaccination is given to infants at two, three and four months: a booster dose is given at around the age of five. The vaccine contains all three types of polio virus. Two types of vaccine are available: inactivated polio virus (IPV) contains dead virus and is administered by injections; oral polio vaccine (OPV) contains live, harmless strains. The latter is used in the United Kingdom.

Symptoms 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 a variable extent, depending on the distribution of the virus – to widespread PARALYSIS. Involvement of the diaphragm and intercostal muscles may lead to respiratory failure and rapid death unless artificial respiration is provided. Involvement of the cranial nerves and brain may lead to nystagmus (see under EYE, DISORDERS OF), hoarseness and difficulty in swallowing, and CONVULSIONS may occur in young children. The CEREBROSPINAL FLUID shows an early increase in lymphocytes, followed by a rise in protein concentration.

Treatment There is no effective drug treatment for the infection. Treatment 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 the 1950s, when polio epidemics were occurring, respiratory difficulties were treated by placing patients in an ‘iron lung’ – a large, airtight, cylindrical container in which the air pressure was raised and lowered to simulate normal breathing.) In cases of severe paralysis with persistent wasting of the limbs, surgery may be necessary to minimise the resulting disability.

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Medical Dictionary

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