Poliomyelitis is a viral disease that can affect nerves and can lead to partial or full paralysis. It is caused by infection with the poliovirus which can be spread by direct person-to-person contact, by contact with infected mucus or phlegm from the nose or mouth, or by contact with infected feces. There are three basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic.
Symptoms vary based on the pattern of infection and can range from asymptomatic with subclinical poliomyelitis to partial or full paralysis. Treatment is aimed at controlling symptoms while the infection runs its course. Since the development of the polio vaccine, the incidence of the disease has been greatly reduced. The prognosis depends on the form of the disease (subclinical, nonparalytic, or paralytic) and the site affected.
Post-polio syndrome (PPS) is a condition that can affect polio survivors decades after they recover from their initial poliovirus infection. Most people who get infected with poliovirus (about 72 out of 100) will not have any visible symptoms.
About 1 out of 4 people with poliovirus infection will have flu-like symptoms that may include:
- Sore throat
- Stomach pain
These symptoms usually last 2 to 5 days, then go away on their own.
More serious symptoms
A smaller proportion of people with poliovirus infection will develop other, more serious symptoms that affect the brain and spinal cord: Paresthesia (feeling of pins and needles in the legs) Meningitis (infection of the covering of the spinal cord and/or brain) occurs in about 1 out of 25 people with poliovirus infection Paralysis (can’t move parts of the body) or weakness in the arms, legs, or both, occurs in about 1 out of 200 people with poliovirus infection. Paralysis is the most severe symptom associated with polio, because it can lead to permanent disability and death. Between 2 and 10 out of 100 people who have paralysis from poliovirus infection die, because the virus affects the muscles that help them breathe. Even children who seem to fully recover can develop new muscle pain, weakness, or paralysis as adults, 15 to 40 years later. This is called post-polio syndrome.
Note that “poliomyelitis” (or “polio” for short) is defined as the paralytic disease. So only people with the paralytic infection are considered to have the disease.
Poliovirus is very contagious and spreads through person-to-person contact. It lives in an infected person’s throat and intestines. Poliovirus only infects people. It enters the body through the mouth and spreads through: Contact with the feces (poop) of an infected person. Droplets from a sneeze or cough of an infected person (less common).
You can get infected with poliovirus if: You have feces on your hands, and you touch your mouth. You put in your mouth objects like toys that are contaminated with feces. An infected person may spread the virus to others immediately before and up to 2 weeks after symptoms appear. The virus can live in an infected person’s feces for many weeks. It can contaminate food and water in unsanitary conditions. People who don’t have symptoms can still pass the virus to others and make them sick.
Prevention & Treatment
There are two types of vaccine that can prevent polio:
Inactivated poliovirus vaccine (IPV) given as an injection in the leg or arm, depending on the patient’s age. Only IPV has been used in the United States since 2000.
Oral poliovirus vaccine (OPV) is still used throughout much of the world.
Polio vaccine protects children by preparing their bodies to fight the poliovirus. Almost all children (99 children out of 100) who get all the recommended doses of the inactivated polio vaccine will be protected from polio.
Poliovirus can be detected in specimens from the throat, feces (stool), and occasionally cerebrospinal fluid (CSF) by isolating the virus in cell culture or by detecting the virus by polymerase chain reaction (PCR).
CDC laboratories conduct testing for poliovirus, including:
- Intratypic differentiation
- Genome sequencing
- Virus Isolation and Detection
Virus isolation in culture is the most sensitive method to diagnose poliovirus infection. Poliovirus is most likely to be isolated from stool specimens. It may also be isolated from pharyngeal swabs. Isolation is less likely from blood or CSF.
To increase the probability of isolating poliovirus, collect at least two stool specimens 24 hours apart from patients with suspected poliomyelitis. These should be collected as early in the course of disease as possible (ideally within 14 days after onset).
Real-time reverse transcription PCR is used to differentiate possible wild strains from vaccine-like strains (“intratypic differentiation”), using virus isolated in culture as the starting material.
Partial genome sequencing is used to confirm the poliovirus genotype and determine its likely geographic origin.
Serology may be helpful in supporting the diagnosis of paralytic poliomyelitis, particularly if a patient is known or suspected to not be vaccinated. An acute serum specimen should be obtained as early in the course of disease as possible, and a convalescent specimen should be obtained at least 3 weeks later.
Cerebrospinal Fluid Analysis
Detection of poliovirus in CSF is uncommon. CSF usually contains an increased number of leukocytes [from 10 to 200 cells/mm3 (primarily lymphocytes)] and a mildly elevated protein (from 40 to 50 mg/dL). These findings are nonspecific and may result from a variety of infectious and noninfectious conditions.