- Polio is an infectious disease caused by viruses. The symptoms may range from none to paralysis and death.
- Polio has been traced back almost 6,000 years. Great strides have been made in preventing this disease.
- Polio is caused by person-to-person transmission of polio viruses (enteroviruses, three main types).
- Not receiving the polio vaccine is the highest risk factor for getting infected with poliovirus. The viruses are only spread human to human by direct and indirect contact.
- Symptoms and signs of polio vary from no symptoms to limb deformities, paralysis, and death.
- Diagnosis of polio is based on the patient's history, physical exam, and ongoing symptoms. The virus may be isolated from the patient's tissues to confirm the diagnosis.
- There is no cure for polio; treatment is mainly supportive and is aimed at limiting or reducing the patient's symptoms.
- For most patients, the prognosis is good because there are few or no symptoms; however, the prognosis declines rapidly as some patients develop more severe symptoms such as limb deformity, paralysis, difficulty breathing, and/or inability to swallow foods.
- It is possible to prevent polio by vaccination; it may be possible to eradicate polio.
- There are at least two types of polio vaccine (intramuscular injection or oral attenuated live vaccine), and both types are effective in preventing polio.
- A polio-like illness has recently been discovered in California in children that produces paralysis like that seen in some polio patients. This illness is not polio, according to doctors treating the children.
What is polio?
Polio is in infectious disease that is caused by viruses that may result in a
wide range of symptoms in patients. Other terms for polio include poliomyelitis
and infantile paralysis. Symptoms can range from a non-paralytic flu-like
infection to total paralysis that can occur within a few hours.
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Non-Polio Enterovirus Disease
What is Non-Polio Enterovirus Disease?
Enteroviruses are a group of viruses that include the polioviruses (viruses that cause polio) along with other types of viruses called coxsackieviruses and echoviruses. Rhinoviruses (viruses that cause the common cold) are the most common viruses infecting humans. The second most common viruses infecting humans are the non-polio enteroviruses (all the members of this virus group excluding the polio-causing viruses).
What is the history of polio?
The history of polio dates back about 6,000 years. Egyptian mummies have been found with withered and malformed limbs that likely occurred because of polio infection. In 1789, the first description of polio was recorded and in 1834 the first documented epidemic occurred on the island of St. Helena. In 1855, Dr. Guillaume Benjamin Amand Duchenne showed polio involved the anterior horn cells of the spinal cord. The Iron lung was developed in the late 1920s to help people with polio breathe. One of the most famous people who had polio was U.S. President Franklin D. Roosevelt (1882-1945). The polio virus was first cultivated in tissue culture (1949), and in 1951, the three types of poliovirus were isolated and identified. During 1954, the first large-scale trial of the vaccine developed by Dr. Jonas Salk (dead virus vaccine) was administered by injection, and in 1958, Dr. Albert Sabin's vaccine (live attenuated virus) was administered orally. In 2000, the U.S. switched to using inactivated polio vaccine by injection. Other countries still may use the oral polio vaccine. Because polio viruses survive only in humans and are transmitted only by human contact, the World Health Organization (WHO) is trying to eradicate polio worldwide. This attempt has been relatively successful with a 99% decrease in polio infections worldwide. However, some countries in Africa and the Middle East still have new infections caused by polio because of areas that cannot be reached by vaccine workers. Unfortunately, when there is war in these regions, polio makes a comeback because vaccine efforts are interrupted. The WHO still believes that polio may be eradicated like smallpox in the near future.
Picture of iron lung used to move air in and out of lungs by pressure changes; SOURCE: CDC/GHO/Mary Hilpertshauser
What causes polio?
Polio is caused by small RNA viruses. They are members of the enterovirus group of the Picornavirus family. There are three types (types 1, 2, and 3) of polio viruses; type I is responsible for about 85% of all paralytic infections. These types are antigenically distinct strains of viruses and infection or immunity to one type does not protect against the other two types, however, if immunity is established to one or all of the three strains, immunity is lifelong. The problem that these viruses cause is the destruction of spinal cord cells (specifically, the anterior horn cells).
What are risk factors for polio? How does polio spread?
Currently, the World Health Organization (WHO) have certified that the Americas, Western Pacific, and Europe are polio free. Other areas have a low incidence of polio, but people in war zones where vaccinations have been interrupted are at a risk getting polio (for example, Afghanistan and Syria). The greatest risk factor for polio is not being vaccinated. People with immunodeficiency (HIV, cancer patients, chemotherapy patients, for example), very young individuals, pregnant females, caregivers for polio patients, travelers to areas were polio is endemic, and lab personnel who work with live polioviruses are at increased risk for polio.
Polio, like smallpox, only infects humans. Polio spreads by person-to-person contact; the virus lives in the throat and in the intestines and is spread through contact with the feces or by droplet spread in a sneeze or cough. It can also be spread by an infected person who has contaminated food or fluids by touching or tasting them. Unfortunately, a person can be infectious and transmit the virus even before they develop any symptoms.
What are polio symptoms and signs?
Fortunately, the vast majority of patients who are infected with polioviruses showed little or no symptoms and, in fact, don't know that they actually had an infection with polioviruses. Those patients who do show symptoms can be placed in one of two major groups; non-paralytic polio (minor) and paralytic polio (major).
Non-paralytic polio infections develop flu-like symptoms that consist of fever, sore throat, headache, malaise, and muscle stiffness (neck, back). These symptoms last about 10-20 days and they completely resolve. Although paralytic polio symptoms mimic the non-paralytic polio symptoms for about a week, increasing symptoms of severe muscle aches and spasms, loss of reflexes, and flaccid paralysis (limbs become floppy) begin to develop. In some individuals, the paralysis may occur very quickly (within a few hours after infection occurs). Sometimes the paralysis is only on one side of the body. The musculature involved with breathing may become inhibited or nonfunctional, and these patients need assistance with breathing.
Post-polio syndrome describes symptoms that develop in patients about 30 to 40 years after an acute polio illness. The cause is unknown. Post-polio syndrome symptoms include
Slowly progressive muscle weakness (any muscles, including the eye muscles and sometimes termed bulbar polio), generalized fatigue, and cold intolerance may also occur.
How do physicians diagnose polio?
A physician may make a preliminary diagnosis of polio from the patient's
history and physical examination. For example, if the patient has not been
vaccinated and has had contact with individuals who have polio and has symptoms
such as muscle stiffness and difficulty with limb movements, breading or
swallowing, then a preliminary diagnosis is made.
A definitive diagnosis is done by cultivating poliovirus from the patient's
mucus, stool, and/or cerebrospinal fluid. In addition, there are serological
tests that detect antibodies directed against poliovirus.
What is the treatment for polio?
Once the virus that causes polio has infected a person, there is no treatment that will cure polio. Early diagnosis and supportive treatments such as bed rest, pain control, good nutrition, and physical therapy to prevent deformities from occurring over time can help reduce the long-term symptoms due to muscle loss. Some patients, unfortunately, may require extensive support and care.
For example, some require breathing assistance and special diets if they have difficulty swallowing while other patients may require splints and/or leg braces to avoid extremity pain, muscle spasms, and limb deformities. Some improvement in the symptoms may occur over time, but this improvement is not easily predictable and varies from patient to patient. For example, patients who needed breathing assistance could be treated with the iron lung. Over time, some would improve and no longer would require iron lung therapy.
What is the prognosis of polio?
The prognosis for patients with polio depends on the extent of damage caused by the poliovirus. Many patients may have few if any symptoms and will have an excellent prognosis. However, the prognosis worsens when patients begin to show symptoms of paralysis, especially with decreased ablility ot breathe or swallow. Many patients who develop more severe polio symptoms progress to lifelong disabilities or death.
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Is it possible to prevent polio? Is there a polio vaccine?
It is possible to prevent polio with vaccination. Vaccinating individuals, especially young children, can establish lifelong immunity to the disease. The inactivated polio vaccine needs to be given at 2, 4, and between 6 and 18 months of age with a booster between ages 4-6. In 2002, the inactivated polio vaccine was approved to be used as a shot combined with diphtheria, tetanus, pertussis, and hepatitis B vaccines. However, the CDC still recommends that people traveling to countries were polio is present receive a polio booster shot before they travel. In addition, those people who care for polio patients need to be sure they have been appropriately vaccinated and still should use strict hygiene when caring for those patients.
Although some people who get the inactivated polio vaccine may have a sore area at the shot site, most people have no problems with the vaccine injection, which usually causes no scar formation. (Smallpox vaccines often left a small scar at the inoculation site.)
Picture of a child receiving the oral polio vaccine
In 2014 in California, an outbreak of an illness that resembled polio was identified which retrospectively dated back to 2012. It is now called acute flaccid myelitis. All of the affected children (about 59 through July 2015) developed a rapid onset of paralysis in one or more limbs and MRI findings were consistent with injury to the central spinal cord. All of the children had been vaccinated against polio. Some of the children were positive for enterovirus-68, a virus known to be associated with limb paralysis and breathing difficulties. The CDC and researchers are currently trying to definitively determine the cause of this illness although they agree it is not polio.
To date, the children, ranging ages 2 to young adults, have not responded to steroid or immunoglobin treatments, with only 16% gradually improving over time. This new outbreak of polio-like illness is being intensely investigated.
Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease
Kotz, Deborah. "Paralysis in children linked to polio-like virus, but it's rare." The Boston Globe Mar. 3, 2014. <https://www.bostonglobe.com/lifestyle/health-wellness/2014/03/03/how-worried-should-about-new-polio-like-virus/D44YZgt3mKHSLgQLdvXYnN/story.html>.
United States. Centers for Disease Control and Prevention. "Global Health - Polio." Sept. 3, 2014. <http://www.cdc.gov/polio/>.
Vidyadhara, S. "Poliomyelitis." Medscape.com. Jan. 15, 2014. <http://emedicine.medscape.com/article/1259213-overview>.