Polio, also known as poliomyelitis and infantile paralysis, is a highly contagious viral infection that can lead to paralysis, breathing problems, or even death.
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.
Fast facts on polio
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:
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.