14.5: The Strange Case of Polio


Polio had long been a relatively rare disease of infants, called “infantile paralysis.” In the middle of the twentieth century, however, it became more common and started affecting older children and adults. A new form of the disease seemed to be emerging.

Human Health and Hygiene

Which of these people, do you think, performed the greatest service to human health and hygiene in the twentieth century, but inadvertently triggered this mid-century polio epidemic?

1. Louis Pasteur, discoverer of pasteurization
2. Alexander Fleming, discoverer of penicillin
3. Jonas Salk, creator of the polio vaccine
4. Franklin Delano Roosevelt, President of the United States and polio victim
5. Henry Ford, creator of the production line.

This seems a strange question, with industrialist Henry Ford under consideration. But indeed, the answer is Henry Ford!

At the beginning of the twentieth century, most local transportation was by horse and powered, of course, almost entirely by the biofuel hay. While it has now largely left social memory, in the early decades of the twentieth century the streets were a slurry of gravel and horse manure. Flies were everywhere, and caused little concern paid, for this was the norm. People’s outhouses were ventilated to the open air, and flies laid eggs there and in the streets, then freely entered houses and landed on food. A number of diseases take advantage of the fecal–oral pathway, and polio is one of them.

But automobiles and tractors intervened. As the horse-drawn era closed, manure generally vanished, running water arrived and flush toilets arrived, hygiene improved, sealed screen doors became common, and flies died in vast numbers. Without intending it, Henry Ford became the greatest ﬂy killer of all time. The availability of the fecal–oral pathway diminished, and the infectivity of related diseases fell.

Figure $$PageIndex{1}$$ shows the horse population declining slowly until World War I, then falling rather steadily as the number of cars increased in stages. The first increase in the number of cars ended around 1930 with the Great Depression, when many people could not afford cars. The end of World War II in 1945 brought another boom in car purchases, and by 1975 society had replaced almost every horse per capita with a car.

As the chance of catching polio fell, the average age of catching it increased. To understand this, consider residents of the northern hemisphere living at various latitudes. Because residents of the High Arctic have a chance to see the northern lights—the aurora borealis—every week, children living there will likely see the aurora before their first birthday. Farther south, at 50 degrees north latitude, the aurora may appear only once every few years, especially near the lights of cities, so a child could be 5 or 10 years old before ever seeing it. And finally, say at 35 degrees north latitude, the aurora may appear but once or twice in a lifetime, so many people could be in middle age before viewing them, and others might go an entire lifetime without being touched by their hypnotic display.

So it is with disease. The number of opportunities for catching a highly infectious disease, naturally, is high. If the quantity of pathogens in the environment is such that all individuals encounter them on average once a year, only about one-third of infants will avoid infection in their first year. (Actually the number is 1/e = 0.367..., if the chance of infection is completely random.) The same fraction of the remaining infants will catch the disease during their first year, and the rest will be age two or older when they catch the disease. Therefore, as the pathways for transmitting polio diminished during the twentieth century, the chances of catching it in any year decreased and the age of onset correspondingly increased.

Polio is like some other diseases that are not usually virulent in infants and young children. A baby infected with polio might have a cold and a runny nose, and the infection might go without particular notice. In an older child, however, it can stop bone growth and muscle development, crippling the child. The polio epidemic of mid-century America was thus not a new disease emerging, but an ancient disease dying out.

Albert Sabin, of polio vaccine fame, suspected a connection with flies. In 1941 he and his colleagues reported in Science on a study they performed in areas of the United States where polio had struck. They captured flies, pureed them in sterile fluid, and gave them to monkeys in feedings, nosedrops, or injections. As they put it, “Down came the monkeys with polio.”

With further improvements in hygiene and broad use of vaccines, rates of polio have dropped to nearly zero. Figure 14.8 shows a moderate number of cases of polio before the late 1940s, an outbreak lasting until the early 1960s, nearly nothing in the years following.

This page titled 14.5: The Strange Case of Polio is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Clarence Lehman, Shelby Loberg, & Adam Clark (University of Minnesota Libraries Publishing) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.