Overview
Polio is a highly infectious disease caused by poliovirus. WHO states that it can invade the nervous system and cause total paralysis within hours, and that it mainly affects children under five years of age.
Most people who catch polio never look ill, which is how the virus spreads unnoticed. There is no cure, so everything rests on vaccination. WHO reports that wild poliovirus cases have fallen by over 99% since 1988.
Disease Summary
- Category
- Infectious Disease
- Cause
- Poliovirus
- Transmission
- Faecal-oral route, and contaminated water or food
- Body System
- Nervous System
- Preventable
- Yes
- Curable
- No
Symptoms
Common Symptoms
Most infections cause no symptoms at all. When symptoms do occur they usually appear as a short flu-like illness lasting 2 to 5 days.
Fever
Fever is among the first symptoms of polio infection and is easily mistaken for any common childhood illness.
Tiredness
General fatigue is listed by WHO among the initial symptoms.
Headache
Headache is one of the earliest symptoms and can be severe.
Sore Throat
CDC lists sore throat among the flu-like symptoms that affect about one in four infected people.
Nausea and Vomiting
Vomiting is listed by WHO among the initial symptoms, reflecting where the virus first multiplies.
Stomach Pain
CDC lists stomach pain among the flu-like symptoms, which usually last 2 to 5 days.
Stiff Neck and Back
Neck and back stiffness signals irritation of the lining of the brain and spinal cord, which CDC reports in about 1 to 5 of every 100 infections.
Pain in the Limbs
Pain in the arms or legs is listed by WHO among the initial symptoms and can precede weakness.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
Sudden Weakness or Paralysis of an Arm or Leg
CDC describes sudden floppy weakness of one or more limbs with reduced or absent reflexes, usually affecting one side more than the other, 7 to 21 days after infection.
Difficulty Breathing
WHO states that 5 to 10% of paralysed people die when the muscles used for breathing become paralysed.
Difficulty Swallowing, Drooling or a Hoarse Voice
These indicate that the nerves controlling the throat are affected, which carries a much higher risk of death.
Stiff Neck or Back With Fever
This signals inflammation of the lining of the brain and spinal cord and needs immediate assessment.
Any Sudden Limb Weakness in an Unvaccinated Person
CDC classifies suspected polio as immediately notifiable and extremely urgent, whatever the eventual diagnosis turns out to be.
Diagnosis
Clinical History
CDC advises considering polio in anyone with sudden limb weakness plus a history of fever or stomach upset, and asking about vaccination status, travel and contact with cases.
Neurological Examination
CDC directs clinicians to examine for floppy weakness and to document muscle tone, reflexes and strength. Sensation is preserved, which helps separate polio from other causes.
Examination of Spinal Fluid
A lumbar puncture is done to assess inflammation of the lining of the brain, though CDC notes the virus itself is rarely found in spinal fluid.
Imaging of the Spine
An MRI showing involvement of the grey matter of the spinal cord supports the diagnosis and triggers stool collection and formal reporting.
Surveillance for Acute Flaccid Paralysis
Every case of sudden floppy weakness in a child is investigated, whatever the cause. This is how countries prove they remain free of polio.
Laboratory Tests
Virus Isolation From Stool
CDC calls this the most sensitive method of diagnosing poliovirus infection. Samples must be collected within the first 14 days after paralysis begins.
Throat Swab
Less likely to be positive than stool. CDC states a negative throat result does not exclude polio.
PCR With Strain Typing
Distinguishes wild poliovirus from vaccine-related strains. This single result determines the entire public health response.
Genetic Sequencing
CDC uses partial genome sequencing to confirm the virus type and work out where it came from, linking a case to a chain of transmission.
Antibody Blood Test
Supports the diagnosis, particularly where a person is known or suspected to be unvaccinated.
Treatment
Supportive Care
There is no licensed treatment for poliovirus infection. CDC states that only supportive care for symptoms is available, and WHO states plainly that polio cannot be cured, only prevented.
Breathing Support
Sustains breathing when the muscles used for breathing are paralysed. This is the point at which lives are saved or lost.
Physiotherapy and Rehabilitation
Preserves and restores movement in weakened limbs, prevents contractures and maintains independence.
Braces, Orthopaedic Shoes and Surgery
Supports weakened limbs, corrects deformity and keeps people walking. This is where most of the difference to a person’s life is made.
Managing Complications and Post-Polio Syndrome
Treats chest and urinary infections, pain and the later weakness and fatigue that many survivors develop decades afterwards.
Prevention
Complete the childhood polio vaccine schedule
WHO recommends a first dose at 6 weeks of age with four doses in the primary series. CDC reports that four doses protect over 99% of vaccinated children.
Vaccinate every child, every round
WHO states that as long as a single child remains infected, children in all countries remain at risk.
Wash hands with soap and water
CDC specifically warns that alcohol-based hand rubs do not work against poliovirus, so soap and water is required after using the toilet and before handling food.
Safe water and sanitation
The virus spreads by the faecal-oral route, so clean water and proper sewage disposal cut transmission directly.
Report every case of sudden floppy weakness
Immediate notification of suspected cases is what triggers the outbreak response.
Vaccination for travellers
Travellers to or from affected countries may need a documented polio vaccine dose, and requirements change, so check before travelling.
Risk Factors
Children Under Five
WHO states polio mainly affects children under 5 years of age.
- Children who have not completed the vaccine schedule
- Children in communities with low coverage
- Children in areas with poor sanitation
- Around 70% of infections in children cause no symptoms, so the virus spreads silently
People in Areas With Ongoing Transmission
Some countries continue to report wild or variant poliovirus.
- Communities in the remaining endemic countries
- Countries reporting variant poliovirus outbreaks
- Travellers to and from affected areas
- Communities where vaccination rounds have been interrupted by conflict
Adolescents and Adults Who Catch Polio
Polio is more dangerous the later in life it is caught.
- Unvaccinated adults, in whom CDC reports a much higher death rate than in children
- People with involvement of the throat and breathing muscles
- Unvaccinated adults travelling to affected areas
- Adults in communities where childhood vaccination was never available
People With Weakened Immunity
A weakened immune system changes how the body handles the virus.
- People with inherited antibody deficiencies
- People on treatment that suppresses the immune system
- People living with advanced untreated HIV
- These groups can carry and shed virus for long periods
Complications
Permanent Paralysis
WHO states that one in 200 infections leads to irreversible paralysis, usually of the legs. CDC reports that residual paralysis remains in about two thirds of paralytic cases.
Breathing Failure
WHO states that 5 to 10% of paralysed people die when their breathing muscles become paralysed.
Weakness of the Swallowing and Breathing Nerves
Involvement of the nerves controlling the throat and airway carries a far higher risk of death than limb paralysis alone.
Inflammation of the Lining of the Brain
CDC reports this in 1 to 5 of every 100 infections. It usually lasts 2 to 10 days and resolves without paralysis.
Post-Polio Syndrome
CDC reports that 25% to 40% of people who had paralytic polio develop new muscle weakness, fatigue and joint pain 15 to 40 years later. It is not contagious.
Chest and Urinary Infections
People with significant paralysis are prone to chest infections from difficulty swallowing and to urinary infections from bladder weakness.
When to Seek Medical Care
Any Sudden Weakness or Paralysis in an Arm or Leg
This is treated as an emergency at any age, and CDC directs that health authorities are contacted immediately.
Difficulty Breathing
Weakness of the breathing muscles is the mechanism of death in paralytic polio.
Stiff Neck or Back With Fever, or Severe Headache
These indicate involvement of the lining of the brain and need assessment the same day.
Difficulty Swallowing or a Change in Voice
Signs that the nerves supplying the throat are affected, which is the most dangerous form.
If an Unvaccinated Person Has Been in Contact With a Case
Or if a child’s vaccinations are overdue. Both are reasons to contact a health worker promptly.
Prognosis
Most Infections Resolve Completely
CDC reports that around 70% of infections in children cause no symptoms, and about 24% produce a minor illness with recovery in under a week.
Paralysis Is Usually Permanent
WHO states that one in 200 infections leads to irreversible paralysis, and CDC reports that residual paralysis remains in about two thirds of paralytic cases.
Outcome Is Worse in Adults
CDC reports a considerably higher death rate in adolescents and adults than in children, and higher still where the throat and breathing muscles are involved.
New Weakness Can Appear Decades Later
CDC reports post-polio syndrome in 25% to 40% of paralytic polio survivors 15 to 40 years after the original illness.
Differential Diagnosis
Guillain-Barre Syndrome
Causes weakness that is usually symmetrical and ascends from the legs upwards, unlike the uneven pattern of polio, and poliovirus testing is negative.
Other Enterovirus Infections
Related viruses can cause sudden floppy weakness. Only laboratory typing separates them from polio.
West Nile Virus Infection
Can cause weakness with a similar pattern and is separated by specific testing and by a history of mosquito exposure.
Botulism
Causes descending weakness beginning in the face and throat, without fever, and is confirmed by toxin testing.
Nerve Injury or Compression
A single injured nerve causes weakness limited to that nerve’s territory, with altered sensation, unlike the preserved sensation of polio.
References
World Health Organization: Poliomyelitis
WHO fact sheet on the disease, the global eradication effort and vaccination.
CDC: Clinical Overview of Poliomyelitis
Clinical presentation, examination findings and diagnostic approach.
CDC: Poliomyelitis, Pink Book
Detailed chapter on the virus, clinical forms, complications and vaccination.
CDC: Laboratory Testing for Poliovirus
Specimen types, collection timing and the tests used to confirm poliovirus.
Frequently Asked Questions
Is polio gone?
Not quite. WHO reports that wild poliovirus cases have fallen by over 99% since 1988, from an estimated 350 000 cases a year in more than 125 countries to endemic transmission in only two. Variant polioviruses that emerge where vaccination coverage is low still cause outbreaks in a number of countries, so vaccination continues.
Can polio be cured?
No. WHO states there is no cure for polio and that it can only be prevented. CDC states that no licensed treatment exists and that only supportive care is available. Paralysis, once it happens, is permanent.
How many polio doses does my child need?
WHO recommends a first dose at 6 weeks of age and four doses in the primary series. CDC reports that four doses protect over 99% of vaccinated children. National schedules differ, so follow the one where you live.
How do people catch polio?
WHO states that poliovirus spreads from person to person mainly by the faecal-oral route, or less often through contaminated water or food, and multiplies in the intestine. People shed the virus in stool for 3 to 6 weeks, including those who never feel ill.
What is post-polio syndrome?
CDC describes it as a slow, irreversible worsening of muscle weakness, fatigue and joint pain that appears in polio survivors 15 to 40 years after the original illness. It affects an estimated 25% to 40% of survivors and it is not contagious.