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An infection caused by poliovirus types 1, 2, and 3. Most patients are asymptomatic; 5–10% develop symptoms (fever, myalgias), and 0.1% develop the paralytic form of the disease (1).
- Polio is a biphasic illness; paralysis occurs in the second phase.
- Polio is spread by direct fecal–oral contact and is common in warmer months.
- Virus is secreted for weeks in stool.
- Poliomyelitis syndromes:
- Bulbar: produces cranial nerve paralysis
- Spinal: causes weakness in the extremities, particularly the legs and a flaccid-type paralysis
- Postpolio syndrome (PPS)
- Atrophy of muscle groups unaffected by original illness in polio patients, usually many years after acute illness
- System(s) affected: nervous; musculoskeletal
- Synonym(s): infantile paralysis; acute anterior poliomyelitis; acute lateral poliomyelitis
Extremely rare; primary vaccination not recommended (except if a patient is traveling to endemic areas)
Most common in children, between 3 months and 16 years of age; infection extremely rare in the United States since the introduction of routine vaccination (1)
A risk factor for developing polio (incidence and severity of polio are increased in pregnant women)
- Eliminated in the United States. Incidence worldwide has dropped >99% since global polio eradication efforts began in 1988.
- Small outbreaks after importation in areas where polio elimination has occurred; rarely as vaccine-associated paralytic polio (VAPP) and in outbreaks occasionally caused by circulating vaccine-derived poliovirus (cVDPV) where oral polio vaccine (OPV) used
- In 2017, three countries remain polio endemic: Afghanistan, Nigeria, and Pakistan.
- Worldwide: In 2016, 37 cases of paralytic polio due to wild poliovirus (type 1) and 5 cases due to cVDPV were reported. Previous worldwide reports were 359 in 2015 and 416 in 2013 (2).
- No wild-virus cases of polio in the United States. In 2014, cases of polio-like illnesses were reported in California. Patients presented with acute paralysis and anterior horn abnormalities. No polio virus was isolated, and the specific etiology remains unknown.
Etiology and Pathophysiology
- Poliovirus is spread by fecal–oral contact and initially infects the GI tract. Viral replication takes place within the GI epithelium, tonsillar, intestinal, and mesenteric lymph nodes. Hematogenous spread to CNS is rare and results in paralytic polio due to destruction of neuronal tissue.
- Pharyngeal spread (less common) is the prevalent mode of transmission in areas with good hygiene.
- Person-to-person spread is most common, followed by contaminated water and sewage.
- Three serotypes of poliovirus (genus Enterovirus):
- Type 1 most frequently associated with epidemics
- Types 2 and 3, sometimes associated with VAPP
- Poor sanitation, hygiene, and public health infrastructure
- Unimmunized status, especially if <5 years of age
- Vaccination using inactivated poliovirus vaccine (IPV) in industrialized countries
- Vaccination using bivalent (types 1 and 3) OPV in endemic or at-risk countries
- No causal link between the polio vaccine and Guillain-Barré syndrome
- In developing countries, treat water sources to prevent spread.
Commonly Associated Conditions
- IM injections or trauma during the prodrome of paralytic polio are thought to precipitate paralysis.
- Tonsillectomy is a risk factor for bulbar paralysis.