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As the name of the disease indicates, there is an infection/ inflammation of the grey matter of the spinal cord (Polios, grey + myelos, marrow + itis, inflammation), causing paralysis of the muscles of the body, especially of the limbs.

The disease is still common, although it can pe prevented by vaccination.

The poliovirus is an enterovirus, i.e. the virus proliferates in the intestine (enteron, intestine) of the patient concerned.

The infection occurs by ingestion of food/water contaminated with poliovirus, and the faecal matter of a patient or a carrier (i.e. the one who carries the poliovirus in the gut, but does not show symptoms of the disease), is the true source of infection.

Flies may play an important role in the spread of the disease, so that epidemics of poliomyelitis may be more common in summer. However, sporadic cases are also seen.

Hence, upgrading hygienic conditions is an important aspect in the prevention of the disease.

The poliovirus may survive even for months in the sewage, i.e., in the waste matter in underground pipes or in various passages. Further, the virus may be passing out in the faeces of patients/carriers for many months, so that the source of infection remains almost continuous, especially during an epidemic.

The poliovirus multiplies in the gut of the man, and apart from passing out in the faeces, it reaches the spinal cord through the various nerves. Or it may enter the blood stream and infect the spinal cord.

The virus has got a particular affinity for the anterior horn cells (i.e. the motor nerve cells in the anterior horns) of the spinal cord, and inflammation/ damage of these cells is responsible for the paralysis of the muscles of the body. Since the anterior horns of the spinal cord are involved, the disease is also called anterior poliomyelitis, and since the disease occurs abruptly, it is more precisely called acute anterior poliomyelitis.

In the whole spinal cord, two of its regions, i.e., the lumbar and the cervical are mainly/usually involved, and out of these two areas, the lumbar region is more involved, so that in a case of poliomyelitis, the legs are more involved than the arms.

Since only motor nerve cells are involved, there is no sensory loss/impairment in the involved limb, in any of the cases of poliomyelitis.

However, besides the lumbar and cervical portions of the spinal cord, the thoracic portion of the cord may also be damaged, leading to the paralysis of the muscles of the thorax, causing difficulty in breathing. Even respiratory paralysis may occur, and the patient may be in a state of grave emergency.

In addition to the spinal cord, the lower portion of the brain, i.e. the brain stem may be affected in some of the cases. This may cause paralysis of the muscles of the face, of the larynx and of the throat, so that the patient may have both difficulty in speaking and in swallowing. When this happens, the patient's condition becomes very serious, and treatment of such cases is only possible in a well-equipped hospital.