Polio: An Infectious Disease of Epidemic Proportions

FROM THE LECTURE SERIES: An Introduction to Infectious Diseases

By Barry C. Fox, M.D., University of Wisconsin

Poliomyelitis, commonly known as polio, is one of the dangerous infectious diseases of the 20th century. It is a contagious viral illness that can easily infect infants and young children and cause nerve injury, leading to paralysis and, in some cases, death. Outbreaks of this disease increased rapidly in the early 1900s in the United States.

A 3D illustration of the polio virus.
Caused by a virus, polio mostly infects infants and young children. (Image: nobeastsofierce/Shutterstock)

Polio Outbreaks in the United States

In his book, Polio: An American Story, David O’Shinsky describes the first recorded outbreak in the United States in 1894 near Rutland, Vermont. In the early 20th century, the United States saw a drastic rise in polio outbreaks, especially in New York.

In 1916, all children leaving New York City were required by the health department to get a travel certificate proving they were polio-free. However, the epidemic continued to spread, including to Hyde Park, the home of Franklin Delano Roosevelt.

Roosevelt Takes Action

It is believed that Roosevelt had his wife and five children remain out of the U.S. on an island off the Canadian coast during the summer of 1916 to keep them from getting the virus.

In that summer, 27,000 Americans died, 80 percent of whom were children under the age of five years. And in 1921, Roosevelt himself acquired polio.

Seven years after contracting the illness, Roosevelt founded the National Institute for Infantile Paralysis, transforming the landscape of polio research. The foundation, which later changed its name to the March of Dimes, was the first private large-scale effort against a single disease.

Learn more about how to stay out of the hospital.

How Does Polio Spread?

It was not until the 1930s, with the invention of the electron microscope, that scientists identified the virus that caused polio. The virus struck quickly without warning, causing mass hysteria among the people that it infected.

Polio is an intestinal virus infection that is spread person-to-person through contact with fecal waste, unwashed hands, shared objects, and contaminated food and water. It enters the body through the mouth, travels into the digestive tract, and is eventually excreted. The small intestine is found to be the main breeding ground for the virus.

Surprisingly, the most common infection it produces is actually an asymptomatic infection meaning with no signs or symptoms, or with minor symptoms such as nausea and a headache.

But in a small percentage of cases, the virus travels via the bloodstream to the brain or the spinal cord, destroying nerve cells called motor neurons, which are responsible for stimulating muscles to contract.

This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now, on The Great Courses Plus.

The Iron Lung

A polio patient in an iron lung.
In 1927, the first iron lung was developed that saved many lives during the peak of the polio epidemic. (Image: Everett Collection/Shutterstock)

The extent and permanence of the resulting paralysis are difficult to predict, as some infected nerve cells will fight off the virus and others will die. At its worst, polio can cause irreversible paralysis, most often of the legs.

The majority of deaths occurred when the breathing muscles were immobilized.

Many patients were kept alive on machines known as iron lungs, an early feat of biomedical engineering, where patients were confined in a tank respirator.

The first iron lung was developed in 1927 at Harvard University, powered by a pump and two vacuum cleaners. The pump changed the pressure inside the airtight metal box, pulling air in and out of the lungs, and this invention was responsible for saving many lives during the peak of the polio epidemic.

Learn more about the immune system: our great protector.

The Development of Polio Vaccine

There was an intense effort to develop a vaccine against polio. In 1953, just after an epidemic year where 58,000 new cases of polio were reported, an American medical researcher, Dr. Jonas Salk, announced on the radio that he had successfully tested a polio vaccine from killed virus strains. He even tested it on himself and his family.

After conducting clinical trials on over two million schoolchildren, the vaccine was deemed safe and effective. It was widely distributed, and the total number of polio cases dropped below 6,000 in the U.S. in 1957, when the vaccine was widely available.

Oral Polio Vaccine

In 1962, another scientist, Albert Sabin, developed a live weakened oral polio vaccine. But this vaccine had to be tested abroad since the Salk vaccine was entrenched in the United States.

Interestingly, Sabin was able to conduct extensive polio vaccine trials in the Soviet Union at the height of the Cold War because the fear of polio was stronger than political differences.

In the first five months of 1959, 10 million children in the Soviet Union received the Sabin oral vaccine, and he received a medal of gratitude from the Russian government during the height of the Cold War.

Both Salk and Sabin donated the rights to their vaccines, unpatented, as gifts to humanity.

Global Efforts to Eradicate Polio

A baby receiving the polio vaccine by mouth.
After the polio vaccine was developed in the mid-20th century, the number of polio cases dropped drastically. (Image: Gorlov-KV/Shutterstock)

In 1987, the WHO launched a global initiative to eradicate polio from the planet within 15 years.

Since 2012, as a result of the global efforts to eradicate the disease, only three countries—Afghanistan, Nigeria, and Pakistan—had polio cases, and this was reduced from more than 125 countries in 1988.

By the year 2000, there were fewer than 2,000 cases worldwide. In spite of all the efforts, eradication of polio remained elusive and the virus, like Ebola, was spreading via international travel. In spite of knowing the epidemiology of the disease, the world’s population is still at risk.

Polio reappeared in Syria after a 15-year absence and continues to persist in Pakistan, Afghanistan, parts of Africa, and Iraq. It is particularly concerning in war-torn areas where even with vaccines available, people are difficult to reach, or people are refusing vaccination.

However, innovative technologies are providing better and faster tools for diagnosis that enable scientists and doctors to contain many outbreaks before they spread throughout countries and continents.

Common Questions about Polio

Q: What causes polio?

Polio is caused by an intestinal virus that is highly contagious.

Q: In what ways does polio spread?

Polio is spread person-to-person through contact with fecal waste, unwashed hands, shared objects, and contaminated food and water.

Q: Who successfully tested a polio vaccine?

In 1953, an American medical researcher, Dr. Jonas Salk, announced that he had successfully tested a polio vaccine from killed virus strains.

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