Poliomyelitis

I

Introduction

Poliomyelitis, infectious viral disease, commonly called polio, that sometimes causes temporary or permanent paralysis. The infection chiefly affects children and young adults. More than 95 percent of polio infections produce no noticeable symptoms or mild symptoms that last only a few days. In the remainder the virus enters the nervous system and infects nerve cells that control muscles. It can then cause paralysis, most often of the legs. In its most dangerous form, the polio virus attacks the brain, creating complications that sometimes result in death. Because of polio’s prevalence among young children, it was sometimes called infantile paralysis.

Polio once ranked among the most dreaded diseases in much of the world. The disease most often struck in summer and early fall. Fearing infection, many people avoided beaches, public pools, theaters, fairs—any place of public gathering. Occasionally schools were closed until epidemics subsided. Paralysis was frightening. Especially terrifying was the thought of lying immobile in an “iron lung”—an artificial breathing device for polio patients who could no longer breathe by themselves.

The fight against polio represents one of the great medical success stories of the 20th century. In much of the world, polio went from a feared disease to mostly a memory in little more than half a century. The introduction of vaccines that protect against polio in the 1950s, along with successful vaccination programs, virtually wiped out polio in developed countries. Vaccination efforts continue in developing countries of Asia and Africa.

II

How Polio Spreads and Develops

The poliovirus spreads in human feces. People become infected with the virus through contaminated food and water, especially in areas where sanitation and hygiene are poor. Improper sewage disposal, for example, can contaminate a water supply.

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Poliovirus typically enters the body through the mouth and proceeds through the digestive tract to the intestines. After multiplying in the body, the virus is shed in the feces, from which it can spread and cause further infections, especially when infected people do not wash their hands and touch food or other people. Adults can become infected by changing the diapers of an infected infant and then touching their mouth.

The poliovirus multiplies in the tonsils and in intestinal tissue known as Peyer’s patches, where cells of the body’s lymphatic system are concentrated. When the virus passes into the body’s lymphatic system, it stimulates the production of antibodies—immune-system defenders that work to destroy the viral intruders. From the lymphatic system, the virus typically invades the bloodstream.

III

Forms of Polio

Once the poliovirus enters the bloodstream, it causes one of three forms of polio that vary in severity. In more than 95 percent of polio cases, the infection produces only mild symptoms or none at all. Sometimes, however, the virus invades the nervous system, causing more severe forms of polio.

A

Abortive Poliomyelitis

Abortive poliomyelitis is a mild form of the disease that lasts only from a few hours to a few days. If symptoms occur, they may include fever, headache, sore throat, fatigue, nausea, or vomiting—many of the symptoms typical of the flu. For the vast majority of people infected with the poliovirus, the illness gets no worse.

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