Polio can be classified as occurring with or without symptoms. About 95 percent of all cases are asymptomatic, and between 4 and 8 percent of cases are symptomatic.
This MNT Knowledge Center article will look at the causes, symptoms, and history of polio, as well as the steps for eradicating polio completely.
Here are some key points about polio. More detail and supporting information is in the main article.
- Polio is caused by the poliovirus.
- The vast majority of polio infections present no symptoms.
- Polio has been eradicated in every country of the world except for Nigeria, Pakistan and Afghanistan.
- Pregnant women are more susceptible to polio.
- Around half of the people who have had polio go on to develop post-polio syndrome.
What is polio?
Jonas Salk, featured on this 1999 stamp, pioneered the polio vaccine.
Polio is a viral infection that can cause paralysis and death in its most severe forms.
It can spread easily from person to person.
The World Health Organiation (WHO) aim is to eradicate polio completely and, if this happens, it will be only the third disease to have been beaten in this way, after smallpox and rinderpest.
Nigeria, Pakistan, and Afghanistan are the only three countries in which polio has not successfully been stopped. The reach and spread, however, has been reduced in these areas over time.
The WHO hopes to achieve the complete eradication of polio by 2018.
Polio, in its most severe forms, can cause paralysis and death. However, most people with polio do not display any symptoms or become noticeably sick. When symptoms do appear, they differ depending on the type of polio.
Symptomatic polio can be broken down further into a mild form, called non-paralytic or abortive polio, and a severe form called paralytic polio that occurs in around 1 percent of cases.
Many people with non-paralytic polio make a full recovery. Unfortunately, those with paralytic polio generally develop permanent paralysis.
Non-paralytic polio symptoms
Non-paralytic polio, also called abortive poliomyelitis, leads to flu-like symptoms that last for a few days or weeks. These include:
- sore throat
- back and neck pain
- arm and leg stiffness
- muscle tenderness and spasms
- meningitis, an infection of the membranes surrounding the brain
Paralytic polio symptoms
Paralytic polio affects only a small percentage of those invaded by the polio virus. In these cases, the virus enters motor neurons where it replicates and destroys the cells. These cells are in the spinal cord, brain stem, or motor cortex, which is an area of the brain important in controlling movements.
Symptoms of paralytic polio often start in a similar way to non-paralytic polio, but later progress to more serious symptoms such as:
- a loss of muscle reflexes
- severe muscle pain and spasms
- loose or floppy limbs that are often worse on one side of the body
Paralytic polio may also be classified as:
- Spinal polio: The virus attacks motor neurons in the spinal cord that causes paralysis in the arms and legs, and breathing problems.
- Bulbar polio: The virus affects the neurons responsible for sight, taste, swallowing, and breathing.
- Bulbospinal polio: The virus causes symptoms of both spinal and bulbar polio.
Complications and post-polio syndrome
Post-polio syndrome describes a cluster of symptoms that affect up to 64 percent of all polio patients. It occurs several years after polio has passed. On average, post-polio syndrome occurs 35 years after the infection.
Signs and symptoms include:
- muscle and joint pain and weakness that slowly progresses
- muscle atrophy or shrinkage
- exhaustion for no reason
- swallowing and breathing difficulties
- suffering in colder temperatures
- sleep-related problems, such as apnea
- concentration and memory difficulties
- mood swings and depression
Post-polio syndrome is a slow, progressive disease. There is no cure, but it is not infectious or contagious.
Polio is often recognized because of symptoms, such as neck and back stiffness, abnormal reflexes, and trouble with swallowing and breathing. A doctor who suspects polio will perform laboratory tests that check for poliovirus by examining throat secretions, stool samples, or cerebrospinal fluid.
There are two vaccines available to fight polio:
- inactivated poliovirus (IPV)
- oral polio vaccine (OPV)
IPV consists of a series of injections that start 2 months after birth and continue until the child is 4 to 6 years old. This version of the vaccine is provided to most children in the U.S. The vaccine is made from inactive poliovirus. It is very safe and effective and cannot cause polio.
OPV is created from a weakened form of poliovirus. This version is the vaccine of choice in many countries because it is low cost, easy to administer, and gives an excellent level of immunity. However, in very rare cases, OPV has been known to revert to a dangerous form of poliovirus, which is able to cause paralysis.
Polio vaccinations, or boosters, are highly recommended for anyone who is not vaccinated or is unsure whether they are.
Because there is no cure for polio once a person develops the virus, treatments are focused on increasing comfort, managing symptoms, and preventing complications. This can include bed rest, antibiotics for additional infections, painkillers, ventilators to help breathing, physiotherapy, moderate exercise, and a proper diet.
Historically, a person who developed lung paralysis due to polio was placed into an iron lung, a device that would push and pull chest muscles to make them work. However, more modern portable ventilators and jacket-type ventilators are now used instead.
Humans have observed the effects of polio for hundreds of years, if not thousands. The relatively recent history of outbreaks in both the United States and Europe has led to an allocation of resources with which to fight the disease.
Throughout history, polio epidemics have led to the deaths of many thousands of people around the world. In 1916, for example, over 6,000 people died of polio in the U.S.
However, it wasn't until 1953 that Jonas Salk developed the first polio vaccine, which has led to the widespread prevention of poliomyelitis.
Although polio has essentially been eradicated in the U.S. since 1979, and in the Western Hemisphere since 1991, children and adults in Afghanistan and Pakistan are still battling the disease.
Polio is caused by the poliovirus.
The polio virus usually enters the environment in the feces of someone who is infected. In areas with poor sanitation, the virus easily spreads from feces into the water supply, or, by touch, into food.
In addition, because polio is so contagious, direct contact with a person infected with the virus can cause polio.
Individuals who carry the poliovirus can spread it via their feces for weeks, even if they have shown no symptoms themselves.
Once the virus has entered an individual, it infects the cells of the throat and intestine.
The virus stays within the intestines, before spreading to other areas of the body. Eventually, the virus moves into the bloodstream where it can spread to the entire body.
As is the case with many other infectious diseases, people who get polio tend to be some of the most vulnerable members of the population. This includes the very young, pregnant women, and those with immune systems that are substantially weakened by other medical conditions.
Anyone who has not been immunized against polio is especially susceptible to contracting the infection.
Additional risk factors for polio include:
- traveling to places where polio is endemic or widespread, especially Pakistan and Afghanistan
- living with someone infected with polio
- having a weak immune system
- pregnant women are more susceptible to polio, but it does not appear to affect the unborn child
- working in a laboratory where live poliovirus is kept
Vaccines are the main way to prevent polio.
However, other methods of limiting the spread of this potentially fatal disease include:
- avoiding food or beverages that may have been contaminated by a person with poliovirus
- checking with a medical professional that your vaccinations are current
- being sure to receive any required booster doses of the vaccine
- washing your hands frequently
- using hand sanitizer when soap is not available
- making sure you only touch the eyes, nose, or mouth with clean hands
- covering the mouth while sneezing or coughing
- avoiding close contact with people who are sick, including kissing, hugging, and sharing utensils
Be sure to receive a vaccination before traveling to an area that is prone to polio breakouts. You can check for up-to-date information about these areas on the Centers for Disease Prevention and Control (CDC) website.