Introduction tp Poliomyelitis

1. Introduction to Poliomyelitis

Poliomyelitis is an infectious disease epidemic and endemic throughout the world. It is caused by one of three types of an ultra-microscopic virus. It is transmitted by droplet infection and by oral ingestion, the latter probably being much the more important mode of transmission in developing countries. The incubation period varies from three to thirty days, while seven to fourteen days is the most common interval between infection and the clinical illness.The disease in the 1990's mainly affects children under five in the developing countries of the tropics and subtropics, but many cases still occur each year in Europe and in other temperate climates. The age of onset in the developed countries, however, is higher, and in Europe unimmunised adults are affected more commonly than children. In the non-immune the virus can cause a generalised disease which can be divided into three parts - an initial incubation period., a prodromal non-paralytic stage, and a definitive paralytic illness. Only a small proportion of those infected ever become ill, however, and less than half of those who become ill ever become paralysed.

The paralysis is made worse by injections or exercise in the prodromal phase, and any, or all, of the limbs and trunk may be affected. The respiratory or swallowing muscles, or both, may also be affected, and may require urgent treatment to save the patient's life.

The residual effects of polio are due to destruction of the anterior horn cells of the spinal cord and the brain stem. This causes a lower motor neurone type of paralysis with flaccid paralysis and normal sensation.The muscles affected depend on which level of the spinal cord is involved, but the paralysis tends to affect some muscles more than others, and the lower limb much more often than the upper limb. As a result of this, contractures are liable to occur, and this is mainly due to imbalance of muscles. These deformities are seen particularly in the lower limbs where the flexors of the hip, knee and ankle are often less paralysed than the extensors. Flexion contractures of the hip and knee, and equinus deformity of the ankle are therefore common sequelae.

Treatment in the early convalescent stage is mainly directed at treating muscle pain and spasm and to preventing these deformities. This latter is achieved by gently stretching muscles daily, and by fitting splints and supporting calipers at an early stage.

Some degree of muscle recovery usually occurs, but many paralysed patients will need calipers permanently to support unstable limbs, especially where the residual power in the limb is less than that necessary to hold the limb up against gravity. Crutches may also be required, but the upper limbs must be strong enough to use them.

Contractures prevent the fitting of calipers, and either cause patients to walk badly or prevent walking at all. The contractures should always be straightened in children, but only if the patient will thereby be enabled to walk, or, in the case of the upper limb, otherwise benefited. Some adults with severe bilateral lower limb contractures in developing countries, are best left crawling or given a wheelchair, especially if weak arms are associated with severe deformities.

Children with calipers should be followed up at least once every six months to renew outgrown and outworn supports. They will also require education and rehabilitation so that they can be given every opportunity to be independent in the future.

Every adult patient must also be regarded as a human being rather than a pair of paralysed limbs, and treatment must be geared to his individual needs, and his rehabilitation to his entire future.

The prevention of further cases of poliomyelitis is essential if this disease is to be eradicated. This is best achieved by an oral polio vaccine (Sabin) manufactured with all three types of attenuated live virus. At least two; and preferably three (and sometimes more) doses should be given to all children and to all babies from the age of three months onwards. Intensive immunisation campaigns are necessary in the developing countries of the world. This is because, paradoxically, the likelihood of epidemics will increase rather than decrease as the infant mortality falls below 80 and the health of the community improves for reasons which are discussed in the chapter on epidemiology.

Epidemics of paralytic poliomyelitis in the developing countries of the tropics and subtropics have, in fact, shown a threefold increase in the past 10 years and are continuing to increase. Nationwide immunisation campaigns are therefore an urgent necessity for all developing countries and, once started, must continue if future epidemics are to be prevented.