Polio – Causes, Signs and symptoms


Also called: Asymptomatic Polio, Paralytic Polio, Poliomyelitis, Abortive Polio, Infantile Paralysis, Symptomatic Polio, Nonparalytic Polio, Spinal Polio

Reviewed By:
Robert Daigneault, M.D
Rafiu Ariganjoye, M.D., MBA, FAAP


Polio is a contagious viral infection that can cause paralysis, breathing problems and other difficulties. In about 95 percent of polio cases, patients experience few if any symptoms and the disease fades without any long-term health damage. However, in rare cases, polio can lead to serious health problems and may even be fatal.

Up until the mid-1950s, polio outbreaks occurred with regularity in the summer and fall, causing cases of paralysis and sometimes death in thousands of people, mostly children. The creation of vaccines to prevent polio has essentially eliminated the natural transmission of the disease in the United States and the Western Hemisphere. Worldwide prevention efforts have reduced the number of cases by 99 percent since 1988, according to the World Health Organization. Polio now exists in several Asian and African countries.

Polio is passed from one infected person to others. Unlike other viruses, it cannot be transmitted by animals. A child typically contracts polio through exposure to the fecal matter of an infected person. The virus enters the body through the mouth and begins to multiply in the throat and intestinal tract. It may spread to other areas of the body via the bloodstream and lymph (a clear fluid that travels through the lymphatic system and helps fight infection).

More than 95 percent of polio cases are called subclinical and produce few or no symptoms. Clinical polio includes nonparalytic polio and paralytic polio. Nonparalytic polio generally causes a mild flu-like illness that passes within a week. However, paralytic polio can have much more serious health consequences, including breathing problems and paralysis that may be permanent. Although this form of polio accounts for less than 1 percent of all polio infections, it is fatal for between 2 and 5 percent of children with paralytic polio.

A physician diagnoses polio by looking for symptoms commonly associated with polio, including stiffness in the neck and back, abnormal reflexes and difficulty swallowing or breathing. If polio is suspected, the physician will take a sample of stool, cerebrospinal fluid or a secretion from the throat and send it to a laboratory for analysis. Because polio is extremely rare in developed countries, a complete medical history, including immunization history and recent travel or contact with travelers, will be taken for any suspected polio case.

There is no medicinal cure for polio. Mild cases resolve within a week or two. Treatment efforts for the more serious nonparalytic and paralytic cases focus on waiting for the child to recover, while also ensuring maximum comfort. In cases of paralytic polio, patients may need long-term assistance breathing or walking. In addition, some patients who contracted polio develop post-polio syndrome (PPS) many years after they had the disease. PPS can involve a return of muscle weakness, even in previously unaffected muscles, joint problems, fatigue and sensitivity to cold.Beginning in the 1950s, mass immunizations started to dramatically slow polio’s spread. The use of widespread vaccinations has virtually eliminated polio in the United States. For several decades, two kinds of polio vaccines were available. Today in the United States, only the inactivated polio vaccine (IPV) is used. Children receive these immunizations as part of a series of three to four injections beginning at 2 months of age and ending with a booster shot between 4 and 6 years of age. Scientists now believe that polio will be eradicated worldwide in the near future.

About polio

Polio is a contagious viral infection that can manifest in different forms: asymptomatic (without symptoms), abortive or nonparalytic (minor illness) and paralytic (severe form that can cause paralysis). However, in most instances polio is a relatively harmless disease that does not cause long-term damage.

Polio, also called poliomyelitis, became an annual scourge in the United States early in the 20th century. Each summer and fall, outbreaks affected thousands, mostly children, with varying levels of paralysis and breathing problems. It was commonly called infantile paralysis. Fear of the disease was just as great and helped fuel interest in creating a vaccine to prevent it. The first vaccine became available in the 1950s and thousands were immunized. Since then, widespread vaccination efforts have eradicated polio in the United States and most other nations.

Polio is passed from one infected person to others. Unlike other viruses, it cannot be transmitted by animals. A child typically contracts polio through the mouth or nose, and the virus has an incubation period of between three and 35 days. The virus enters through the mouth or nose and multiplies in the throat and digestive tract. In milder forms of polio, the virus typically does not spread any further in the body. A patient with this mild form of polio may only experience mild, flu-like symptoms (abortive or nonparalytic polio). Most patients infected with the poliovirus are frequently without symptoms (asymptomatic polio).

However, in severe cases, the poliovirus enters the bloodstream and lymph (a clear fluid that travels through the lymphatic system and helps fight infection) and attacks the central nervous system. Parts of nerve fibers called motor neurons may be damaged or destroyed. Motor neurons help carry messages between the brain and the muscles and their destruction can cause paralysis of the affected muscles. If the muscles are in the arms or legs, these limbs may be paralyzed. Muscle paralysis in the upper body may also affect breathing and swallowing.

Paralytic polio can cause complications in many body systems, including pneumonia and pulmonary edema, respiratory failure, heart problems, intestinal obstructions, kidney stones and urinary tract infections. In addition to these immediate complications, some patients who recover from polio sometimes experience symptoms that appear 10 to 40 years after the illness. Known as post-polio syndrome, this condition may cause recurrence of weakness or fatigue in previously affected areas of the body or in new areas. In addition to muscle pain, joint pain and problems swallowing and breathing may occur. Other symptoms of post-polio syndrome may include:

  • Decreased ability to tolerate cold temperatures
  • Sleep-related breathing disorders such as sleep apnea

Scientists do not completely understand what causes post-polio syndrome. However, it is believed that it may at least partially result from damage to new nerve fibers that sprout in healthy neurons after a polio infection.

Although polio sometimes has devastating consequences, this is unusual. In the vast majority of cases, patients with polio experience no symptoms. However, this does not mean they are not contagious. People with polio can shed the virus in their stool for weeks or even months after they are infected. In addition, children and adults who are immune to the polio nonetheless can carry the virus. In areas of the world where sanitation is inadequate, a single carrier of the virus can cause hundreds of people to become infected.

Beginning in the 1950s, mass immunizations dramatically slowed polio’s spread. Thanks to widespread use of vaccinations, polio has been virtually eliminated in the United States. The last case of “wild” polio – defined as polio occurring from natural infection – in the United States occurred in 1979. In 1994, polio was declared eradicated throughout the entire Western hemisphere. Scientists now believe that polio will be eradicated worldwide in the near future. Polio only remains endemic, or native, in a few countries in Asia and Africa. Outbreaks occur in other developing nations when people contract it in a nation where polio is endemic and travel to another area where people have not received polio vaccines.

Types and differences of polio

There are two major types of polio: subclinical and clinical polio. The vast majority of polio infections are subclinical, meaning the patient experiences few if any symptoms. About 95 percent of polio cases fall into this category, according to the Centers for Disease Control and Prevention (CDC). In many cases, patients who have subclinical polio are unaware that they have been infected.

Clinical polio can also be subdivided by its degree of severity. The two chief forms of clinical polio are nonparalytic and paralytic.

Nonparalytic polio – also known as abortive polio – is a rare form of the disease that does not cause paralysis. Instead, symptoms mirror those of other viral infections. Between 4 and 8 percent of polio cases are classified as nonparalytic polio, according to the CDC. Typically, nonparalytic polio resolves within a week, although between 1 and 2 percent of patients with polio develop a viral infection of the meninges (covering of the brain and spine) called nonparalytic aseptic meningitis. Most children who have nonparalytic polio or nonparalytic aseptic meningitis make a full recovery.

Paralytic polio is the most serious form of the disease and may cause muscle paralysis and even death. It affects less than 1 percent of all polio patients, but is fatal for 2 to 5 percent of children who are diagnosed with this form of polio, according to the CDC. There are several types of paralytic polio that are sometimes recognized, although the categories are not considered to be rigid. Subtypes include:

  • Spinal polio. This most common form of paralytic polio affects nerve cells in the spinal cord. It may paralyze muscles that control breathing and the arms and legs. The degree of motor neuron damage determines the severity of paralysis. Patients with damaged neurons may eventually recover use of the paralyzed muscles. However, destruction of the neurons results in permanent paralysis, even though the patient may be able to feel sensation in the affected area. Spinal polio accounts for about 79 percent of paralytic polio cases, according to the CDC.
  • Bulbar polio. This form affects the motor neurons of the brainstem, which houses the nerves that govern swallowing and the senses other than touch. These nerves affect the facial muscles and also signal important organs such as the lungs and heart. Children diagnosed with bulbar polio often have problems breathing, speaking and swallowing. Bulbar polio accounts for about 2 percent of paralytic polio cases, according to the CDC.
  • Bulbospinal polio. Combines both the spinal and bulbar forms, causing paralysis of the limbs and affecting breathing, swallowing and cardiac function. Bulbospinal polio accounts for about 19 percent of paralytic polio cases, according to the CDC.

Risk factors and causes of polio

Polio usually is transmitted through exposure to fecal matter of an infected person. In most cases, children become infected through oral exposure to this fecal matter that occurs as the result of poor sanitation. Other sources of polio include drinking contaminated water or eating contaminated food, becoming infected when failing to wash hands after using the bathroom, and person-to-person contact. Changing diapers of an infected infant can also expose a person to the virus.

Polio is highly contagious. Patients who have the disease are most contagious for between seven to 10 days before symptoms appear and after they disappear. However, an infected person can continue to spread the virus by shedding it in their stool for weeks after infection.

Children who have not received their immunization for polio are at greatest risk for contracting the virus. Although the risk is relatively low in the United States, it is not nonexistent. People who travel to the United States from other regions may carry the virus and spread it. In addition, people who travel to developing nations may be at increased risk if they are not immunized. Regular contact with an infected person, or caring for a polio patient, increases the risk of contracting the virus in a person without immunity.

Scientists are not sure why some children develop paralytic polio, while others do not. However, it is believed that certain factors elevate the risk of contracting it, such as a weakened immune system, injury or exercise after viral exposure and mouth or throat surgery (e.g., tonsillectomy) or infection around the time of exposure.

Certain factors also increase the risk of developing post-polio syndrome, a set of symptoms that sometime appear years or decades after a patient’s initial infection with the polio virus. These factors include:

  • Severity of polio infection
  • Extent of recovery – ironically, the greater the recovery, the more likely post-polio syndrome becomes
  • Infection that occurred during adolescence or adulthood rather than childhood
  • History of overexertion, which may stress overworked motor neurons

Signs and symptoms of polio

In the vast majority of cases, patients with polio experience no symptoms and recover from the disease without incident. However, in other cases, symptoms may appear that range from mild to severe.

Symptoms of nonparalytic polio tend to mimic those associated with viral illnesses such as the flu. Also known as abortive polio, it often manifests as sore throat, fever, nausea and vomiting and constipation or diarrhea. Other symptoms include:

  • Excessive fatigue
  • Headache
  • Irritability
  • Muscle tenderness and spasm in any area of the body
  • Neck pain and stiffness
  • Pain or stiffness of the back, arms, legs, abdomen
  • Skin rash or lesion with pain

In about 10 percent of cases, patients with this form of polio may develop nonparalytic aseptic meningitis. This is a viral infection of the outer covering of the brain and spinal cord called the meninges. This condition can last for between two and 10 days, and includes symptoms such as fever, headache, vomiting, diarrhea, fatigue, and muscle spasms or tenderness. In addition, patients may feel pain or stiffness in the back, neck or limbs.

Symptoms related to paralytic polio tend to be much more severe. This form of polio typically begins as a fever that is followed five to seven days later by the same symptoms as nonparalytic polio, in addition to an increased sensitivity to touch. A child’s limbs also may become loose, a condition known as acute flaccid paralysis. This condition often affects just one side of the body, or is worse on one side than on the other.

Other symptoms associated with paralytic polio include:

  • Abnormal sensations (but not loss of sensation) of an area
  • Bloated sensation in the abdomen
  • Difficulty breathing or swallowing problems
  • Constipation
  • Difficulty beginning to urinate
  • Drooling
  • Irritability or poor temper control
  • Muscle pain, contractions or spasms

Diagnosis methods for polio

In diagnosing polio, a physician will perform a complete physical examination and compile a thorough medical history. Particular attention will be paid to symptoms commonly associated with polio, including stiffness in the neck and back, abnormal reflexes and difficulty swallowing or breathing. The medical history is especially important because polio is now rare. History and type of polio vaccination, travel to an infected area or contact with an infected person will be taken into account.

If polio is suspected, the physician will take a sample of stool, cerebrospinal fluid or a secretion from the throat and send it to a laboratory for analysis

Treatment options for polio

There is no medical cure for polio. Treatment efforts focus on waiting for the child to recover while also ensuring maximum comfort and trying to prevent complications. Antibiotics may be used to treat associated infections (such as urinary tract infections) and pain-relieving medications may be used to reduce discomfort. Moist heat is sometimes used to reduce muscle pain and spasms.

Children who have some forms of polio (such as bulbar polio) may need respiratory support to continue to breathe. This may include the use of portable ventilators or a tracheostomy, a surgical opening made in the windpipe. Some patients may be helped by physical therapy to regain use of their muscles or minimize muscle atrophy (partial or complete wasting away of a part of the body). 

Prognosis is excellent for children who contract polio that does not affect the brain or spinal cord. Prognosis is less certain in the small minority of cases where polio does affect the brain or spinal cord. Disability often results, and in rare cases this type of polio can be fatal.

Prevention methods for polio

Vaccination is the most important method for preventing polio. Inactivated polio vaccine (IPV) usually is given to children by injection in four doses: at ages 2 months, 4 months, between 6 months and 18 months, and a booster shot between the ages of 4 and 6 years. In some cases, children only receive three doses if the third dose is given on or after a child’s fourth birthday. Most adults in the United States are immune to polio from their own childhood immunizations. However, new vaccinations may be recommended for adults who may travel to areas where polio is endemic, work with laboratory samples or care for a polio patient.

IPV is 90 percent effective in preventing polio after two shots, and 99 percent effective after three doses. Because the virus used in the vaccine is inactivated, it cannot cause polio. Some children may experience minor side effects after receiving vaccination, including redness or swelling.

IPV also contains trace amounts of certain antibiotics. People with known allergies to these antibiotics should not receive IPV. In rare cases, the vaccine may cause a serious allergic reaction that usually occurs anywhere from minutes to several hours after injection. Symptoms of allergic reaction include high fever, difficulty breathing, weakness, hoarseness or wheezing, fast heartbeat, hives, dizziness, paleness and swelling of the throat. Children who experience any of these symptoms following immunization require immediate medical treatment.

Previously, many children were vaccinated using a live but weakened form of the poliovirus that was administered orally. However, this type of vaccine caused a few children to develop polio. As a result, it no longer is used in the United States. The worldwide polio eradication program still uses the oral polio vaccine.

Questions for your doctor regarding polio

Preparing questions in advance can help patients and parents have more meaningful discussions with their physicians regarding their or their child’s treatment options. The following questions related to polio may be helpful:

  1. Why should I have my child immunized if polio has been eradicated in the United States?
  2. What are the risks and side effects associated with immunization?
  3. What are the signs of polio in my child?
  4. What type of polio does my child likely have?
  5. What are my child’s treatment options?
  6. What is my child’s prognosis?
  7. How can I protect other family members from getting my child’s infection?
  8. Should I alert school authorities, other parents, etc. about my child’s infection?
  9. Will my child need regular monitoring over time to check for signs of post-polio syndrome?
  10. My child is not fully immunized, but will soon be traveling to a country where polio is still present. What precautions are necessary?
  11. I’m traveling to an area where polio still occurs. Is there a chance I’ll infect my children upon my return?
  12. Does the polio vaccine increase risk of autism in children?
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