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Polio: the story on HearLore | HearLore
Polio
Polio is a disease that hides in plain sight, with approximately 75% of all infections producing no symptoms at all. This silent nature allowed the virus to spread through populations for thousands of years before humanity recognized it as a distinct medical condition. While most people who contracted the virus experienced only minor, flu-like symptoms such as a sore throat and fever that resolved within a week, a small fraction of cases progressed to a terrifying outcome. In about one out of every 1,000 infections, the virus migrated from the gastrointestinal tract into the central nervous system, destroying motor neurons and causing acute flaccid paralysis. This form of the disease, known as paralytic poliomyelitis, left victims with weak, floppy muscles that could become completely paralyzed, often affecting the legs but sometimes the muscles of the head, neck, and diaphragm. The destruction of these nerve cells was permanent, and in extreme cases where breathing muscles were paralyzed, the outcome was death. The virus itself is a simple RNA structure enclosed in a protein shell, yet its ability to hijack human cells and replicate within the blood for up to 17 weeks made it a formidable enemy. It does not affect any species other than humans, making the human population its sole reservoir and target.
Shadows of History
The effects of polio have been known since prehistory, with ancient Egyptian steles from the 18th Dynasty, dating between 1403 and 1365 BC, depicting people with withered limbs and children walking with canes. Despite these early depictions, the disease was not clinically described until the 2nd of May 1789, when the English physician Michael Underwood referred to it as a debility of the lower extremities. It was not until 1909 that the Austrian immunologist Karl Landsteiner identified the specific virus responsible for the condition. Before the 20th century, polio was an endemic disease worldwide, meaning it was constantly present in the population. Poor sanitation and hygiene resulted in constant exposure to the virus, which enhanced natural immunity within the population, so infections rarely occurred in infants before six months of age. However, as community sanitation improved during the late 19th and early 20th centuries, the general level of herd immunity declined. This paradoxical effect of better hygiene created circumstances where epidemics of polio became frequent and severe. By 1950, the peak age incidence of paralytic poliomyelitis in the United States had shifted from infants to children aged five to nine years, and the rate of paralysis and death increased accordingly. The 1952 polio epidemic became the worst outbreak in the nation's history, with nearly 58,000 cases reported, 3,145 deaths, and 21,269 people left with mild to disabling paralysis.
What percentage of polio infections produce no symptoms?
Approximately 75% of all polio infections produce no symptoms at all. This silent nature allowed the virus to spread through populations for thousands of years before humanity recognized it as a distinct medical condition.
When was polio first clinically described by a physician?
Polio was first clinically described on the 2nd of May 1789 by the English physician Michael Underwood. He referred to the condition as a debility of the lower extremities.
How many polio cases and deaths occurred during the 1952 epidemic in the United States?
The 1952 polio epidemic resulted in nearly 58,000 cases and 3,145 deaths. Additionally, 21,269 people were left with mild to disabling paralysis during this outbreak.
When was the Salk polio vaccine announced to the world?
The inactivated polio vaccine known as the Salk vaccine was announced to the world on the 12th of April 1955. Jonas Salk developed the vaccine in 1952 at the University of Pittsburgh.
Which countries still have wild polio cases as of 2022?
The last remaining region with wild polio cases remains the South Asian countries of Afghanistan and Pakistan. In 2021, a single case of wild polio was detected in Malawi and another in Mozambique in 2022.
What percentage of polio survivors develop post-polio syndrome?
Between 25 percent and 50 percent of individuals who have recovered from paralytic polio in childhood can develop post-polio syndrome. This condition involves new muscle weakness and extreme fatigue that appears decades after the acute infection.
The fight against polio in the mid-20th century gave rise to modern intensive care medicine, as hospitals struggled to manage patients who could no longer breathe on their own. The most iconic symbol of this era was the iron lung, a noninvasive, negative-pressure ventilator used to artificially maintain respiration during an acute polio infection until a person could breathe independently. These machines were largely obsolete in modern medicine today, but they were life-saving devices for thousands of patients during the epidemics of the 1950s. The first respiratory centers designed to assist the most severe polio patients were established in 1952 at the Blegdam Hospital of Copenhagen by Danish anesthesiologist Bjørn Ibsen, who would go on to establish the world's first dedicated intensive care unit a year later. The disease also spurred grassroots fundraising campaigns that revolutionized medical philanthropy and gave rise to the modern field of rehabilitation therapy. Polio survivors became one of the largest disabled groups in the world, with estimates suggesting 10 to 20 million survivors globally. In 1977, there were 254,000 persons living in the United States who had been paralyzed by polio, and significant numbers were also living in Germany, Japan, France, Australia, Canada, and the United Kingdom. The cultural impact of the disease was profound, as it brought about the modern disability rights movement through campaigns for the social and civil rights of the disabled. The Polio Hall of Fame, dedicated in 1957 at the Roosevelt Warm Springs Institute for Rehabilitation in Warm Springs, Georgia, honors fifteen scientists and two laymen who made important contributions to the knowledge and treatment of poliomyelitis.
The Vaccine Revolution
The development of vaccines in the 1950s marked the turning point in the history of polio, transforming it from a terrifying epidemic into a manageable and eventually eradicated disease. The inactivated polio vaccine, known as the Salk vaccine, was developed in 1952 by Jonas Salk at the University of Pittsburgh and announced to the world on the 12th of April 1955. This vaccine was based on poliovirus grown in monkey kidney tissue culture and chemically inactivated with formalin. After three doses, at least 99 percent of individuals were immune to poliovirus. Subsequently, Albert Sabin developed an oral polio vaccine, known as OPV, which contained a live, attenuated virus. This vaccine was produced by the repeated passage of the virus through nonhuman cells at subphysiological temperatures and was licensed in 1962. The Sabin vaccine was inexpensive, easy to administer, and produced excellent immunity in the intestine, making it the vaccine of choice for controlling poliomyelitis in many countries. However, on very rare occasions, the attenuated virus in the Sabin OPV could revert into a form that could paralyze, leading to circulating vaccine-derived poliovirus cases. An improved oral vaccine, known as nOPV2, was granted full licensure and prequalification by the World Health Organization in December 2023, offering greater genetic stability and a lower risk of reverting to a virulent form.
The Global Eradication
A global effort to eradicate polio, known as the Global Polio Eradication Initiative, began in 1988, led by the World Health Organization, UNICEF, and The Rotary Foundation. This campaign has reduced polio worldwide by 99 percent, bringing the number of cases from an estimated 350,000 in 1988 to just 30 confirmed cases in 2022. By 2015, polio was believed to remain naturally spreading in only two countries, Pakistan and Afghanistan, although it continued to cause outbreaks in other nearby countries due to hidden or re-established transmission. In 2019, wild poliovirus type 2 was certified as eradicated, and in 2021, wild poliovirus type 3 was also certified as eradicated. The Americas were declared polio-free in 1994, and Europe was declared polio-free in 2002. Despite these successes, challenges remain, including the emergence of circulating vaccine-derived poliovirus cases that have occasionally outnumbered wild polio cases. In 2021, a single case of wild polio was detected in Malawi, the country's first in almost three decades, and another in Mozambique in 2022, both of a strain imported from Pakistan. The last remaining region with wild polio cases remains the South Asian countries of Afghanistan and Pakistan, where factors such as the fake hepatitis vaccination clinic run by the CIA in 2011 and attacks on vaccination workers have set back efforts to eliminate the disease.
The Long Shadow of Recovery
For those who survived the acute phase of polio, the disease often left a long shadow that extended decades into their future. Between 25 percent and 50 percent of individuals who have recovered from paralytic polio in childhood can develop additional symptoms decades after recovering from the acute infection, a condition known as post-polio syndrome. This syndrome involves new muscle weakness and extreme fatigue, thought to be caused by the failure of the oversized motor units created during the recovery phase of the paralytic disease. Contributing factors include aging with loss of neuron units, the presence of a permanent residual impairment after recovery from the acute illness, and both overuse and disuse of neurons. The physiological processes involved in recovery following acute paralytic poliomyelitis are quite effective, with muscles able to retain normal strength even if half the original motor neurons have been lost. However, paralysis remaining after one year is likely to be permanent, although some recovery of muscle strength is possible up to 18 months after infection. Complications from prolonged immobility can include pulmonary edema, aspiration pneumonia, urinary tract infections, kidney stones, and paralytic ileus. Orthotics and physical therapy have been essential tools for helping survivors stand and walk safely, with modern materials and functional elements enabling the orthosis to be specifically adapted to the requirements resulting from the patient's gait.