- Polio-like Virus
What is polio?
Polio is an 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.
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 (nerve cells) of the spinal cord. Landsteiner and Popper discovered the virus in 1908. The Iron lung was developed in the late 1920s to help some polio survivors 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 the mid-1950s (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 as an oral vaccine. In 2000, the U.S. switched to using inactivated polio vaccine by injection. Other countries still may use the oral poliovirus 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. In 2014, WHO announced that Southeast Asia was polio-free. 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 eradication, like smallpox, may happen in the near future.
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).
Currently, the World Health Organization (WHO) has 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 risk of 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 where 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 (fecal-oral spread) or by droplets 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.
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What are the symptoms of polio?
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 groups; non-paralytic polio (minor) and paralytic polio (major).
Non-paralytic polio symptoms:
- Non-paralytic polio infections develop flu-like symptoms that consist of fever, sore throat, headache, malaise, and muscle stiffness (neck, back).
- Some people may get a skin rash that resembles a measles rash type. These symptoms last about 10-20 days and they completely resolve thus termed nonparalytic polio.
Paralytic polio symptoms:
- Although paralytic polio symptoms mimic the nonparalytic 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. The post-polio syndrome symptoms include
- muscle pain,
- joint pain, and
- spinal changes such as scoliosis, spondylosis, and/or secondary nerve root and peripheral nerve compression.
Diagnosis of 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, in the past, patients who needed breathing assistance would be treated with the iron lung. Over time, some would improve and no longer would require iron lung therapy.
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What is the prognosis for 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 ability to breathe or swallow. Many patients who develop more severe polio symptoms progress to lifelong disabilities or death.
Is it possible to prevent polio? Is there a polio vaccine?
It is possible to prevent polio by stimulating your immune system 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 where 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.
Because oral polio vaccine has weakened (attenuated) but live viruses (not as effective as wild-type polio viruses in causing symptoms), occasionally some of the weakened oral vaccine viruses may pass through the feces and infect other people. This is rare; the WHO reports fewer than 760 people worldwide vaccine-derived after administering over 10 billion oral doses.
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 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 from 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 by agents from the U.S. Centers for Disease Control and Prevention.
Switzerland. World Health Organization (WHO). "What Is Vaccine-Derived Polio?" April 2017. <http://www.who.int/features/qa/64/en/>.
United States. Centers for Disease Control and Prevention. "Global Health - Polio Eradication." Dec. 20, 2017. <http://www.cdc.gov/polio/>.
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