Symptoms and transmission of polio

Polio, short for poliomyelitis, is an infectious disease that is caused and transmitted by a virus called the poliovirus. One of the severe symptoms of polio is paralysis and the disease is therefore also known as “infantile paralysis”. The name poliomyelitis is derived from Greek and translates to gray (polios) marrow (myelon), which refers to the tissue in the center of the spinal cord, which when affected causes paralysis. Paralyzed limbs such as arms or legs waste away over time which is the cause of deformed child legs most commonly being associated with the disease polio.

The symptoms vary widely between patients. Most infections do not lead to any symptoms, but others suffer terribly and for some it leads to death. Between 1 in 50 and 1 in 500 infections result in paralysis, among people who have not been vaccinated.²

The majority of infections (72%) do not lead to any symptoms. About a quarter of cases (24%) result in “abortive” poliomyelitis which leads to nonspecific symptoms for a few days, such as a fever or a cold, and 1-5% of cases lead to “non-paralytic aseptic meningitis”, in which the patient suffers from stiff limbs for up to 10 days.³

The poliovirus is found only among humans and is transmitted via the so-called fecal-oral route. In other words, polio is mostly transmitted by drinking water that has been contaminated by the feces of a person carrying the poliovirus. The virus therefore spreads especially well in conditions of poor sanitation, for example when people defecate in the open or do not filter their water before drinking it. The fact that the virus can only survive in humans (and no other animals) makes it possible to completely eradicate the disease from the world – if it was a virus with an animal host such as influenza (birds) or tuberculosis (cows) that occasionally mutates to attack humans, polio could only ever be controlled but not eradicated.

Its relatively long incubation period of up to 10 days and three fourths of infections not showing any symptoms makes polio extremely difficult to monitor and the virus can spread for several months without being detected. Monitoring has to focus on identifying patients that suffer from symptoms or rely on stool samples. Because single identified cases might indicate larger outbreaks, the WHO recommends to treat such cases as a public health emergency when only one child is identified with a wild, endemic polio infection in a country that was previously declared polio free.⁴

Fighting polio’s symptoms: The ‘Iron Lung’

Polio can lead to the death of infected patients when the paralysis is immobilizing their breathing muscles.⁵To prevent the death by suffocation, Harvard professors Philip Drinker and Louis Agassiz Shaw invented the so called “iron lung”⁶ (shown in the picture) in 1928. Infected patients would be placed in an air-tight tube – with their heads outside – and the machine decreased the pressure inside the box, to induce inhalation, before returning to the normal outside pressure conditions, to induce exhalation. Most patients would spend one to two weeks in an iron lung before their paralytic symptoms faded and independent breathing was achieved once again. In the case of permanent paralysis, on the other hand, patients would be bound to live inside the iron lung for years.

As it is often the case with innovations, the iron lung became only widespread when the price declined substantially. John Emerson managed to construct an iron lung at half the cost in 1931. In the meantime, Philip Drinker had tried to protect his invention with a patent and therefore filed a lawsuit against Emerson for using the original iron lung set-up. Emerson did not succumb, claiming that life-saving devices should be made available to the public at low cost rather than be used for private financial gains, and in the end, Drinker’s lawsuit failed.⁷

The falling price of the Iron Lung enabled mass distribution and widespread use from the end of the 1930s onwards. The cost of one iron lung in the 1930s amounted to US-$1,500, which is the equivalent of approximately US-$26,000 in 2016 when accounting for inflation.⁸

The design quickly spread to Western Europe and was widely used for polio patients there, too.

The data visualization further below, which shows the prevalence of polio in the US over the last century, shows two large outbreaks in 1916 and 1952. It can be seen that in 1916, before the widespread use of iron lungs, the death rate increased sharply when the case rate increased. But after the widespread use of iron lungs from 1939 onwards and during the largest polio outbreak in the US in the 1950s the death rate did not show the same strongly correlated increase anymore. This is because the breathing assistance of the iron lungs prevented the deaths of the many polio patients suffering from paralyzed breathing muscles – the iron lungs were a large step forward in mankind’s struggle against polio.