Update on Polio and Post-Polio Syndrome

BY ALL RIGHTS, polio should be extinct, alongside smallpox. And yet, not only is polio still with us — although eradication comes closer year by year — more than 100,000 Americans still suffer from or will yet develop post-polio syndrome.

After several decades as one of humanity’s true nightmare diseases (the kind of illness that kept parents awake at night worrying for their children, the sort of malady that caused families to flee to the countryside during outbreaks in order to avoid infection), polio became one of medical science’s greatest triumphs: the twin victories of Jonas Salk and Albert Sabin in 1955. Polio, and the resultant paralysis that afflicts approximately one-half of 1 percent of its victims, inspired such dread in the 20th century that even at the height of the Cold War, the Soviet Union awarded Sabin, an American, with the Order of Friendship Among Peoples for his work in helping eradicate polio in Russia.¹ Sabin’s and Salk’s efforts against polio in the West were so successful that few people born after the 1950s have any recollection of how utterly terrifying polio was — the specter of iron lungs and leg braces largely consigned to the history books.

From tens of millions of cases each year in the early 1950s to 350,000 cases globally in 1988, global eradication efforts reduced the number to 359 cases in 2014² — with nearly all of them in Afghanistan or Pakistan. Only those Americans now middle-aged or older who contracted polio before the vaccines were developed, or immigrants who contracted polio before moving here, are still coping with post-polio syndrome or are at risk of developing it.

What Are Polio and Post-Polio Syndrome?

Poliomyelitis, generally shortened to polio, is an incurable but easily prevented infectious disease caused by the poliovirus. Children ages 4 years to 14 years are most susceptible, although the disease is far more dangerous and severe in adults.³

The poliovirus enters its host orally. Once in the intestines, it spreads throughout the body, and in a small number of people, eventually attacks the nervous system (acute poliomyelitis).⁴ While about 70 percent of those infected will suffer no symptoms, and most who do get sick from the infection will have minor flu-like symptoms, about one in 200 people who get the disease will develop what is called acute poliomyelitis and will suffer temporary or permanent paralysis due to damaged nerves in the spinal cord. Of those who develop the acute form of the disease, up to 10 percent will die when the muscles associated with breathing stop working.⁴ Not only was polio one of the most dreaded diseases of the 20th century, it was only in that century that polio epidemics occurred. Prior to the 1900s, polio was a dangerous infection that could cause death or paralysis, but outbreaks were small in number of victims, as well as geographically contained.⁵ It was only with the rapid urbanization that followed the Industrial Revolution in the United States and Western Europe that polio epidemics began to occur in large cities. Some 2,700 cases were reported in New York City alone in a 1907 outbreak. In 1916, more than 6,000 deaths were attributed to polio in the United States.3 Each following year saw at least one major polio outbreak somewhere in the United States, with thousands dying and many tens of thousands paralyzed.

At the time, it was already noted by researchers that children who had been infected and survived gained immunity to the disease.³ It would become apparent that a percentage of those who developed and recovered from acute poliomyelitis faced a recurrence of the symptoms decades later, a condition termed post-polio syndrome, or PPS.⁶

Causes of Polio and PPS

There are three strains of the wild poliovirus, types 1, 2 and 3, differentiated by the proteins in their capsid, or shell. Type 2 is now extinct in the wild, with no new cases reported since 1999.⁷ Types 1 and 3 have now been eradicated from Nigeria in the last few years, leaving Afghanistan and Pakistan as the last nations where wild polio remains extant.

A small number of infections result from the use of the attenuated live-virus Sabin vaccine due to natural mutations that occur when the virus in the vaccine reproduces in the human digestive tract, resulting in a more lethal variety shed through the feces. There were 580 cases identified from 2000 to 2011, during which time more than 15,000 children were paralyzed by wild poliovirus worldwide.⁸

There is no difference in symptoms or mortality between the strains, however. Poliovirus is spread through a feces-oral cycle; its spread is the result of a lack of hygienic practices. Infected food or water or dirty fingers are the primary sources of poliovirus.⁹ The virus reproduces in the intestines, and new viruses are expelled from the host body in the feces during the infection, usually in a matter of a few weeks.

The causes of PPS are presently unknown.6 Researchers have determined that 25 percent to 40 percent of those who develop acute poliomyelitis will later develop PPS, generally 25 years to 40 years after the original infection.

Symptoms and Progression

On average, some 70 percent of patients who contract polio will be asymptomatic and, in fact, wholly unaware they ever were infected.¹⁰ For those who do exhibit symptoms, most will be similar to the flu: fever, nausea, fatigue and general achiness.

The vast majority of patients who develop symptoms will never progress to acute poliomyelitis, but will instead experience a milder version referred to as nonparalytic polio. Those very few cases that progress to acute status, also known as paralytic polio, will see a worsening severity of symptoms within a week: loss of reflexes, severe muscle pain or weakness and loose limbs.¹⁰

The poliovirus attacks motor-control nerve cells in the spinal cord or brain stem; as the muscles are cut off from the brain, they begin to atrophy. In some cases, the paralysis is permanent. But other patients see some eventual improvement. Researchers believe that the body generates new receptors on surviving neurons after a polio infection to make up for the loss of the attacked cells. Over time, these cells may become overworked and begin to give out.⁶

However, some 40 percent of these recovered patients will eventually develop PPS. Symptoms of PPS are a recurrence of muscle weakness, muscle atrophy, general fatigue, difficulty swallowing and increased sensitivity to cold temperatures.¹¹

Diagnosis

A diagnosis of poliomyelitis would be extremely rare for an American or European physician today. However, it is possible if a patient is returning from Afghanistan or Pakistan. Polio is confirmed by examination of stool, throat secretions or spinal fluid for the presence of the poliovirus.

PPS remains a common occurrence in the West, as there are hundreds of thousands who survived a bout with polio as a youngster.

There is no single test to confirm PPS; instead, a physician will consider a battery of different tools to narrow down a diagnosis. These may include:¹²

• A previous diagnosis of acute poliomyelitis. Only those who were infected by the poliovirus will contract PPS.
• Electromyography (EMG). An EMG can help eliminate other possible causes for the symptoms the patient is experiencing.
• Magnetic resonance imaging (MRI) or computerized tomography (CT). An MRI and/or CT can help determine if a spinal disorder is causing the symptoms.
• Biopsy. A small sample of muscle tissue may be removed and examined to eliminate other causes.
• Blood test. A patient with PPS will have a normal blood test, so this test will help eliminate other possible causes.

Treatment

There is no cure for polio or PPS. Treatment for polio is supportive, including bed rest, pain relievers, nutrition and mild physical therapy to try to minimize loss of function.¹³ Treatment for PPS focuses on preserving as much function and quality of life as possible. Physical therapy and pain relievers may be called for to help ease symptoms. The Mayo Clinic suggests working with patients to help them learn energy conservation techniques to cope with their condition.¹⁴

One area showing some promise is the use of intravenous immune globulin (IVIG), which the National Institutes of Health (NIH) indicates shows improvements in pain management and quality of life.6 However, the Mayo Clinic¹⁴ and the Post-Polio Health International both argue that the benefits of IVIG are still unproven.¹⁵

Other treatment approaches have proven either ineffective or harmful. NIH currently advises against the use of prednisone due to the severity of the side effects. Another study on the anticonvulsant lamotrigine showed promise, but the study was limited.⁶

Prevention

Polio is wholly preventable through vaccination, and it may be that 2016 is the year that the last pockets of wild poliovirus are eradicated in Pakistan and Afghanistan, relegating this fearsome disease to the history books. As with smallpox samples stored by U.S. and Russian health authorities in case a new vaccine is ever needed, small samples of poliovirus may exist in secure laboratory facilities for some years as a source of future immunizations.

There is not yet an effective prevention for PPS, although those who have not had acute poliomyelitis are not at risk.

Research

With so few polio patients in the world today, and with multiple vaccines readily available, there is little research into polio treatment. It is likely that within a year or so, polio will be exterminated.

However, we will still have PPS around for some time, and research is ongoing to try to find a way to prevent onset of PPS, as well as effective treatments.

Some areas of study include immunology to see if an autoimmune response is a trigger. Other researchers are looking into the possible roles of fatigue and nutrition as possible triggers for PPS onset.6 However, the NIH clinical trials page listed no ongoing or upcoming trials regarding polio or PPS as of this writing.

Looking Ahead

The technology and infrastructure to eliminate polio from the world exist; what allows polio to continue has been a lack of political will. But with Nigeria now being polio-free, we are very close to the day that polio becomes extinct.

That said, once the last case of polio is reported, we will still have another 80 years or so of a population pool susceptible to developing PPS. And with people moving around the world as never before, physicians everywhere need the proper protocols to diagnose and treat PPS for the foreseeable future.