Poliomyelitis (Polio): Causes, Symptoms & Vaccine
Poliomyelitis (polio) is a highly contagious viral disease that attacks the nervous system and can cause permanent paralysis. Vaccination has largely eradicated it worldwide.
Things worth knowing about "Poliomyelitis"
Poliomyelitis (polio) is a highly contagious viral disease that attacks the nervous system and can cause permanent paralysis. Vaccination has largely eradicated it worldwide.
What is Poliomyelitis?
Poliomyelitis, commonly known as polio or historically as infantile paralysis, is a highly contagious infectious disease caused by the poliovirus. The virus belongs to the family of enteroviruses and primarily targets the nervous system. In severe cases, it destroys motor nerve cells in the spinal cord and brainstem, potentially causing irreversible paralysis. Thanks to global vaccination campaigns, the disease has been eradicated in most countries, though it has not yet been completely eliminated worldwide.
Causes and Transmission
Poliomyelitis is caused by three serotypes of the poliovirus (Type 1, 2, and 3). Transmission occurs mainly through:
- Fecal-oral route: Via contaminated water or food that has come into contact with the stool of infected individuals.
- Droplet transmission: To a lesser extent through respiratory secretions of infected persons.
The virus initially replicates in the intestine and can then enter the bloodstream and subsequently the central nervous system. Unvaccinated individuals and children under five years of age are at the highest risk.
Symptoms
The majority of infections (approximately 70–75%) are completely asymptomatic. However, a proportion of those infected may experience different clinical forms:
- Abortive poliomyelitis: Mild flu-like symptoms such as fever, sore throat, nausea, and abdominal pain, resolving spontaneously within a few days.
- Non-paralytic poliomyelitis (aseptic meningitis): Neck stiffness, headaches, and muscle pain due to inflammation of the meninges without paralysis.
- Paralytic poliomyelitis: The most severe form, occurring in approximately 0.1–1% of infected individuals. It presents as sudden, asymmetric flaccid paralysis, most commonly affecting the leg muscles. Involvement of the brainstem (bulbar polio) can lead to life-threatening respiratory and swallowing paralysis.
Diagnosis
Diagnosis of poliomyelitis is based on clinical findings and laboratory investigations:
- Virus isolation: Detection of poliovirus in stool samples (preferred method), throat swabs, or cerebrospinal fluid (CSF).
- PCR (Polymerase Chain Reaction): Highly sensitive molecular detection of the viral genome.
- Serology: Detection of antibodies against poliovirus in the blood.
- CSF analysis: In cases of suspected meningitis for differential diagnosis.
Treatment
There is currently no specific antiviral therapy for poliomyelitis. Treatment is therefore purely symptomatic and supportive:
- Bed rest and pain relief during the acute phase
- Physiotherapy to preserve and restore muscle function
- Respiratory support (e.g., mechanical ventilation) in cases of bulbar involvement
- Orthopedic aids and rehabilitation for permanent paralysis
Post-Polio Syndrome
Decades after the acute illness, some survivors may develop what is known as post-polio syndrome. This manifests as new-onset muscle weakness, fatigue, and pain, and also requires symptomatic treatment and rehabilitation.
Prevention and Vaccination
The most effective measure against poliomyelitis is vaccination. Two types of vaccine are available:
- Inactivated Polio Vaccine (IPV, Salk vaccine): Administered by injection and contains killed virus particles. It is safe and used in most high-income countries.
- Oral Polio Vaccine (OPV, Sabin vaccine): Contains live attenuated virus and is taken orally. It is easy to administer and widely used in low-income countries, but in very rare cases can itself cause vaccine-associated paralytic polio.
Health authorities worldwide, including the World Health Organization (WHO) and national immunization programs, recommend primary immunization against polio during infancy as part of routine childhood vaccination, with booster doses in adulthood where indicated.
References
- World Health Organization (WHO): Poliomyelitis. Available at: https://www.who.int/news-room/fact-sheets/detail/poliomyelitis (accessed 2024)
- Centers for Disease Control and Prevention (CDC): Polio Disease and Poliovirus. Available at: https://www.cdc.gov/polio (accessed 2024)
- Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th Edition. Elsevier, Philadelphia 2020.
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