Poliomyelitis (Polio)
Summary
Poliomyelitis is a highly infectious viral disease caused by poliovirus (an enterovirus). It is transmitted via the faecal-oral route and primarily affects children under 5 years. While >95% of infections are asymptomatic or cause mild illness, <1% result in irreversible paralytic polio, which occurs when the virus destroys motor neurons in the anterior horn of the spinal cord. This causes asymmetric flaccid paralysis with preserved sensation. Bulbar polio affects brainstem motor neurons and can cause respiratory failure. There is no cure — treatment is supportive. Prevention through vaccination has led to near-global eradication, with wild poliovirus now endemic in only a few countries.
Key Facts
- Cause: Poliovirus (Enterovirus, 3 serotypes)
- Transmission: Faecal-oral
- 95% Asymptomatic: <1% cause paralysis
- Paralysis: Asymmetric, Flaccid, LMN signs, Sensation intact
- Target: Anterior horn cells of spinal cord
- Prevention: Vaccination (IPV, OPV)
- Eradication: Near-global; Endemic in Afghanistan and Pakistan
Clinical Pearls
"LMN Signs, Sensation Intact": Polio destroys motor neurons only — sensation is preserved.
"Asymmetric Paralysis": Unlike GBS, polio paralysis is typically asymmetric.
"Post-Polio Syndrome": Deterioration decades later due to surviving motor neurons failing.
"Vaccination Changed Everything": Polio was once the most feared childhood disease. Vaccination has nearly eradicated it.
Current Status
- 99% reduction since 1988 (global vaccination campaign)
- Wild poliovirus endemic only in Afghanistan and Pakistan
- Wild type 2 and 3 eradicated; Type 1 remains
Demographics
- Primarily affects <5 years
- Historically affected all ages
Transmission
- Faecal-oral (predominant)
- Oral-oral (saliva) in some settings
Infection Pathway
- Ingestion of poliovirus
- Replication in oropharynx and GI tract
- Viraemia
- Invasion of CNS (in <1%)
- Destruction of anterior horn motor neurons
- Flaccid paralysis
Why Anterior Horn?
- Poliovirus has tropism for motor neurons
- Sensory neurons spared
Bulbar Polio
- Affects brainstem motor nuclei
- Respiratory and swallowing muscles paralysed
- Historically treated with "iron lung"
Spectrum
| Form | Proportion | Features |
|---|---|---|
| Asymptomatic | 95% | No symptoms |
| Abortive | 4% | Fever, Malaise, Sore throat, Nausea |
| Non-paralytic (Aseptic Meningitis) | 1% | Meningism without paralysis |
| Paralytic | <1% | Flaccid paralysis |
Paralytic Polio
| Feature | Description |
|---|---|
| Onset | Sudden, after prodromal illness |
| Paralysis | Asymmetric, Flaccid |
| Reflexes | Absent (LMN) |
| Sensation | INTACT (key differentiator) |
| Distribution | Legs > Arms; Proximal > Distal |
Bulbar Polio
Motor
- Asymmetric flaccid weakness
- Muscle wasting (later)
- Hypotonia
Reflexes
- Absent or reduced deep tendon reflexes
Sensory
- NORMAL (key finding)
Respiratory
- Assess respiratory effort
- Bulbar signs (drooling, weak cough)
Diagnosis
| Test | Notes |
|---|---|
| Stool sample | Virus isolation (gold standard) |
| Throat swab | Virus isolation |
| CSF | Lymphocytic pleocytosis; Normal glucose |
| Serology | Rising antibody titre |
Notifiable
- Polio is a notifiable disease — report immediately
No Cure — Supportive Care
┌──────────────────────────────────────────────────────────┐
│ POLIO MANAGEMENT │
├──────────────────────────────────────────────────────────┤
│ │
│ ACUTE: │
│ • Supportive care │
│ • Bed rest during febrile phase │
│ • Pain relief │
│ • Monitor respiratory function │
│ • Mechanical ventilation if bulbar/respiratory failure │
│ │
│ REHABILITATION: │
│ • Physiotherapy (prevent contractures, maintain ROM) │
│ • Orthotics (splints, braces) │
│ • Orthopaedic surgery (later, for deformities) │
│ │
│ PREVENTION (CRITICAL): │
│ • Vaccination: │
│ - IPV (Inactivated Polio Vaccine — Salk) — Injection │
│ - OPV (Oral Polio Vaccine — Sabin) — Used in │
│ eradication campaigns │
│ • UK uses IPV (in 6-in-1 vaccine) │
│ │
│ POST-POLIO SYNDROME: │
│ • Decades after acute infection │
│ • Progressive muscle weakness, Fatigue, Pain │
│ • Supportive care, Pacing, Physiotherapy │
│ │
└──────────────────────────────────────────────────────────┘
Acute
- Respiratory failure (bulbar polio)
- Aspiration pneumonia
- Death (2-10% of paralytic cases)
Long-Term
- Permanent paralysis
- Limb deformities
- Scoliosis
- Post-polio syndrome (decades later)
Paralytic Polio
- Mortality: 2-10%
- Bulbar polio: Higher mortality (25-75%)
- Paralysis: Usually permanent
Post-Polio Syndrome
- Affects 25-50% of survivors
- Onset 15-40 years after acute disease
- Progressive weakness and fatigue
Key Resources
- GPEI: Global Polio Eradication Initiative
- WHO: Polio Eradication
Key Evidence
Vaccination
- IPV and OPV highly effective
- Global eradication within reach
What is Polio?
Polio (poliomyelitis) is a viral infection that can cause paralysis. It mainly affects young children.
How Do You Catch It?
The virus spreads through contaminated water or food, or through close contact with an infected person.
What Are the Symptoms?
Most people have no symptoms or a mild flu-like illness. In rare cases (<1%), the virus attacks the nerves and causes:
- Sudden weakness or paralysis (usually in the legs)
- Difficulty breathing (in severe cases)
Is There a Cure?
There is no cure for polio. Treatment focuses on supporting the patient and preventing complications.
Can It Be Prevented?
Yes! Vaccination is highly effective and has nearly eliminated polio from the world. In the UK, polio vaccine is part of the routine childhood immunisation schedule.
What is Post-Polio Syndrome?
Some people who had polio as children develop new muscle weakness, tiredness, and pain decades later. This is called post-polio syndrome.
Primary Resources
- Global Polio Eradication Initiative. Polio Eradication. polioeradication.org
- World Health Organization. Poliomyelitis.
Key Studies
- Nathanson N, Kew OM. From emergence to eradication: the epidemiology of poliomyelitis deconstructed. Am J Epidemiol. 2010;172(11):1213-1229. PMID: 20978089