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.
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, also called abortive poliomyelitis, leads to flu-like symptoms that last for a few days or weeks. These include:
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:
Paralytic polio may also be classified as:
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:
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:
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.
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:
Vaccines are the main way to prevent polio.
However, other methods of limiting the spread of this potentially fatal disease include: