Polio

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Poliomyelitis (Polio)

Overview

Poliomyelitis is an acute, highly contagious infection caused by poliovirus - a neurotropic enterovirus (RNA virus, Picornaviridae family). It spreads person-to-person and causes paralysis through destruction of anterior horn motor neurons. Vaccination has nearly eradicated the disease worldwide, but it remains endemic in Pakistan and Afghanistan as of 2026.

There are three serotypes (Type 1, 2, 3). Type 1 is the most paralytogenic and was historically the most common cause of epidemics. Wild poliovirus Type 2 has not been recorded since 1999.

Transmission

Developed countries: Oral-to-oral (respiratory droplets)
Developing countries: Fecal-to-oral (poor sanitation)
Humans are the only natural host
Oral secretion lasts several days; stool excretion can persist for several weeks
Immunocompromised patients are at significantly higher risk

Pathophysiology

The virus enters via the GI tract and replicates in gut-associated lymphoid tissue (GALT). At a critical concentration, viremia carries the virus to the:

Spinal cord anterior horn cells (most common - causes spinal polio)
Brainstem and reticular formation
Vestibular nuclei, hypothalamus, thalamus, cerebellum, and precentral motor cortex

Infected motor neurons die, causing a cycle of muscle denervation and reinnervation, ultimately leading to irreversible muscle atrophy and paralysis. Sensory neurons are characteristically spared.

Clinical Spectrum

Form	Frequency	Features
Asymptomatic	>90% of infections	Silent; still shed virus
Abortive (minor illness)	~5%	Fever, malaise, headache, sore throat, GI symptoms; no neurologic involvement
Non-paralytic (aseptic meningitis)	~1-5%	Meningeal signs, Kernig/Brudzinski signs; resolves in 1-2 weeks
Paralytic	<1-2%	Anterior horn cell destruction; the classic feared form

Paralytic Polio - Key Features

Asymmetric, proximal, flaccid weakness - lower extremities most commonly
Absent tendon reflexes, fasciculations
Sensory function preserved (no sensory deficit on examination despite pain/paresthesias)
Autonomic dysfunction: sweating disturbances, urinary retention, constipation, delayed gastric emptying
Maximal paralysis usually within 5 days
Muscle wasting develops over several weeks
Most patients with spinal polio show improved motor function within the first year

Bulbar Polio

Up to 20% of paralytic cases develop bulbar involvement:

Speech and swallowing dysfunction (dysphagia, dysarthria)
Facial and extraocular muscle weakness
Reticular formation involvement causes cardiac dysrhythmias, BP alterations, hypoxia, and hypercarbia - potentially fatal

Young patient with polio showing paralysis of lower limb and paraspinal muscles causing marked scoliosis and deformed pelvis

Young patient with polio showing paralysis of the lower limb and paraspinal muscles causing marked scoliosis and a deformed pelvis. - Bailey and Love's Short Practice of Surgery, 28th Ed.

Diagnosis

Suspect acute paralytic poliomyelitis when an at-risk patient develops:

Acute febrile illness + aseptic meningitis + asymmetric flaccid paralysis + loss of deep tendon reflexes + normal sensation

Investigations

CSF: Pleocytosis (WBC can be in the hundreds, neutrophil predominance early); elevated protein
Viral culture: Throat and rectal swabs yield more than CSF
Stool samples: Two specimens 24-48 hours apart (highest yield in the first 2 weeks)
Serial serum antibody titers: To verify cultures once serotype identified
Stool samples must be stored at 4-8°C and reach the lab within 72 hours

Differential Diagnosis

Condition	Distinguishing Feature
Guillain-Barre syndrome	Symmetric weakness (most important to exclude)
Transverse myelitis	Sensory level + sphincter disturbance
Acute spinal cord compression	Sensory level present
Coxsackie/Echovirus/Enterovirus	Lab differentiation needed
Spinal muscular atrophy (in children)	No fever prodrome, genetic
Lyme disease, porphyria, infectious mono	Peripheral neuropathies

Treatment

There is no specific antiviral therapy for polio. Management is supportive:

Bed rest during acute phase
Analgesics for pain and muscle spasm
Physiotherapy / rehabilitation: Prevents contractures, maximizes function
Respiratory support: Mechanical ventilation if bulbar/respiratory involvement
Orthopedic interventions (late): Tendon transfers, arthrodesis for residual paralysis - should only be undertaken after careful assessment; most patients learn to live with their disabilities (Bailey & Love)

Post-Polio Syndrome (PPS)

Expected to affect up to 100,000 of the 250,000 U.S. adults who had prior polio. Onset is 20-35 years after initial infection, typically in patients >50 years old.

Characteristics:

New or recurrent muscle fatigue, weakness, pain, atrophy, and fasciculations
Affects previously unaffected AND previously involved muscle groups
New bulbar, respiratory, or sleep difficulties (laryngeal weakness causing dyspnea, dysphagia, hoarseness)
Sleep disturbances managed with benzodiazepines or dopaminergic drugs
Diagnosis of exclusion

Risk factors for earlier PPS onset: Advanced age at initial infection, greater residual motor disability, residual bulbar/respiratory signs, recent limb immobilization

The mechanism is thought to involve dysfunction of nerve axons in surviving motor neurons (not reactivation of poliovirus).

Vaccines

Two main types:

	IPV (Inactivated Poliovirus Vaccine)	OPV (Oral Poliovirus Vaccine)
Type	Killed virus, injectable	Live attenuated, oral
Route	Intramuscular/subcutaneous	Oral drops
Immunity	Systemic (IgG)	Systemic + mucosal (IgA)
VAPP risk	None	1 in 1.4-2.8 million recipients; 1 in 6.7 million contacts
Use	Standard in developed countries	Mass campaigns (developing world)

Vaccine-Derived Paralytic Polio (VAPP): Can occur in immunocompromised OPV recipients, or in unvaccinated contacts of recently vaccinated children. A case of vaccine-derived paralytic poliomyelitis was identified in New York State in July 2022 in an unvaccinated person.
Travelers who completed a primary vaccine series and are traveling to endemic regions should receive a one-time booster dose of IPV (Goldman-Cecil Medicine).

Surveillance & Eradication

Surveillance relies on Acute Flaccid Paralysis (AFP) surveillance - any child under 15 years with AFP must be reported and tested. The benchmark is at least 1 AFP case per 100,000 children under 15 annually as a sensitivity indicator.

Four steps of AFP surveillance:

Find and report AFP cases promptly
Transport stool specimens (two samples 24-48 hrs apart, at 4-8°C, within 72 hrs to lab)
Isolate and characterize poliovirus (wild vs. vaccine-derived)
Map the virus geographically using genetic sequencing

Global eradication milestones:

Wild poliovirus eradicated from the USA in 1979; Western Hemisphere in 1991
Wild poliovirus Type 2 last recorded in 1999
India declared polio-free on 27 March 2014 (last case: Howrah, West Bengal, 13 Jan 2011)
Wild polio currently endemic only in Pakistan and Afghanistan

India's Pulse Polio Immunization (PPI): Mass administration of OPV to all children 0-5 years on a single day, two rounds 4-6 weeks apart during low-transmission season (November-February). First conducted December 1995.

Key Risk Factors for Severe Disease (in developing countries)

Recent intramuscular injections
Prior tonsillectomy
Strenuous exercise
Immunocompromised state

Recent evidence note: A 2025 systematic review (PMID: 41163052) examined immunogenicity and safety of polio vaccines in infants across randomized trials - no findings contradict the above standard guidance on vaccination. A 2025 review (PMID: 40740383) on advances in polio vaccines notes ongoing development efforts but no major changes to current eradication strategy.

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