POLIOMYELITIS

also called infantile paralysis, acute infectious viral disease characterized by symptoms that range from a mild nonparalytic infection to an extensive flaccid paralysis of voluntary muscles. Severe epidemics of poliomyelitis have been reported in many parts of the world. In the United States the greatest recorded sustained incidence was in 194253; in 1950 there were 33,344 cases. In 1952 severe epidemics occurred in Denmark, Germany, and Belgium. In Asia outbreaks were reported in Bombay, Singapore, Japan, Korea, and the Philippines. Since the 1960s, however, poliomyelitis has been more or less under control in the developed world. Control is based on community- or area-wide use of the attenuated live polio vaccine, given orally (Sabin), and the inactivated (killed) injectable vaccine (Salk). The poliovirus is believed to enter the body through the throat. From the alimentary tract it is absorbed into the blood and lymphatics, whence it is widely disseminated throughout the body and ultimately reaches the central nervous system. The most common early symptoms of poliomyelitis are mild headache, fever, sore throat, nausea, vomiting, diarrhea, restlessness, and drowsiness. Temperature rises slowly, and fever peaks in two to three days and then rapidly subsides. More than 80 percent of all patients who develop poliomyelitis recover within three to four days without the development of paralysis. When the disease is severe, the patient becomes irritable and develops pain in the back and limbs, muscle tenderness, and stiff neck. Paralytic poliomyelitis results from the destruction of the anterior horn (motor nerve) cells of the spinal cord. Cells that are destroyed are not replaced because nerve cells cannot regenerate. Cells that are not severely injured recover their normal function in time; to the extent that they do recover, a corresponding restoration of muscle function may be expected. The paralysis may range in severity from transient weakness that soon disappears to complete permanent paralysis, with associated progressive atrophy of the unused muscles. In respiratory poliomyelitis the virus injures the upper part of the spinal cord, with resulting difficulties in breathing. In bulbar poliomyelitis the virus attacks the bulb, or brainstem, situated just above the spinal cord, and the nerve centres that control swallowing and talking are injured. Secretions collect in the throat and may lead to suffocation by blocking the airway. Treatment during the preparalytic stages includes complete bed rest, isolation, and careful observation. If paralysis occurs, passive movement of the limbs can be used to avoid deformities. As muscle strength returns, exercises are increased. Breathing requires mechanical aids such as the iron lung or the positive pressure ventilator, which pumps air into the patient's lungs through a tracheotomy tube inserted in the windpipe. Accumulated secretions in the throat may be removed by a mechanical suction machine. There seem to be individual differences in the degree of natural susceptibility to the disease. Many persons have acquired antibodies to the polio virus in their blood without having had any symptoms of infection. It is generally held that a lasting immunity follows recovery from the disease; but second attacks are known to occur, caused, at least in some cases, by viral strains differing immunologically from those responsible for the first attack. Among the predisposing factors, age is the most important, children and young adults being most often affected. Other predisposing factors include strenuous exercise, sudden chilling, and pregnancy.