5.5.3 Poliomyelitis

Introduction

Poliomyelitis, commonly known as polio, is a highly infectious viral disease caused by the poliovirus. It primarily affects children under the age of five. The virus invades the nervous system and can cause paralysis. While polio has been largely eradicated in many parts of the world due to widespread vaccination, it remains endemic in a few countries. Understanding poliomyelitis is essential for global health efforts to eradicate the disease.

Definition

Poliomyelitis: Poliomyelitis is caused by poliovirus which is also an enterovirus.

In simple words: Poliomyelitis is a viral disease caused by poliovirus that can lead to paralysis.

Core Concept

• Cause: Poliovirus (an enterovirus)
• Transmission: Faecal-oral route
• Replication: Replicates in the oropharynx and intestinal tract; spreads to blood and central nervous system; replicates in the motor neurons located in the spinal cord
• Symptoms: Death of motor neurons results in paralysis of the muscles innervated by these neurons; motor nerve damage is permanent
• Treatment: No antiviral therapy; physiotherapy for the affected muscles is important
• Prevention: Polio can be prevented by:
• Killed vaccine (Salk vaccine, injectable polio vaccine or IPV)
• Live, attenuated (weakened) vaccine (Sabin vaccine, oral polio vaccine or OPV)

Detailed Explanation

Causative Agent

• Poliovirus is a member of the Enterovirus genus.
• It is a non-enveloped virus with an icosahedral capsid.
• It has a single-stranded RNA genome.
• There are three serotypes: PV1, PV2, and PV3.
• PV1 is the most common cause of paralytic polio.

Transmission

• Poliovirus is transmitted by the faecal-oral route.
• It enters the body through the mouth.
• It multiplies in the oropharynx and intestinal tract.
• It can be spread through contaminated water, food, or hands.

Pathogenesis

• The virus replicates in the oropharynx and intestinal tract.
• It spreads to the blood (viremia).
• It spreads to the central nervous system.
• It replicates in the motor neurons located in the spinal cord.
• Death of motor neurons results in paralysis of the muscles innervated by these neurons.
• The motor nerve damage is permanent.

Symptoms

• Most infections are asymptomatic (90–95%).
• Abortive polio causes mild symptoms.
• Non-paralytic polio causes stiff neck and back pain.
• Paralytic polio causes severe muscle pain and paralysis.
• Post-polio syndrome can occur years after recovery.

Treatment

• There is no antiviral therapy for polio.
• Physiotherapy for the affected muscles is important.
• Supportive care includes pain relief, bed rest, and fluids.
• Assistive devices may be needed for mobility.

Prevention

• Polio can be prevented by two types of vaccines:
• IPV is given by injection.
• OPV is given orally.
• Both vaccines are effective in preventing polio.

Comparison of IPV and OPV

Summary Table of Poliomyelitis

Intermediate Level

Causative Agent in Detail

Transmission in Detail

Pathogenesis in Detail

Symptoms in Detail

Treatment in Detail

Prevention in Detail

Important Points

• 1. Poliomyelitis is caused by poliovirus which is also an enterovirus.
• 2. Transmission: Polio virus is transmitted by the faecal-oral route.
• 3. Replication: It replicates in the oropharynx and intestinal tract and spreads to blood and central nervous system where virus replicates in the motor neurons located in the spinal cord.
• 4. Symptoms: Death of these cells results in paralysis of the muscles innervated by these neurons.
• 5. The motor nerve damage is permanent.
• 6. Treatment: There is no antiviral therapy. Physiotherapy for the affected muscles is important.
• 7. Prevention: Polio can be prevented by:
• - Killed vaccine (Salk vaccine, injectable polio vaccine or IPV)
• - Live, attenuated (weakened) vaccine (Sabin vaccine, oral polio vaccine or OPV)

Remember

• - Polio = viral disease
• - Cause = poliovirus (enterovirus)
• - Transmission = faecal-oral
• - Replication = oropharynx, intestinal tract, blood, CNS, motor neurons
• - **Symptoms** = paralysis
• - Treatment = no antiviral; physiotherapy
• - Prevention = IPV (Salk), OPV (Sabin)
• - Motor nerve damage = permanent
• - No cure = but preventable by vaccine

Common Mistakes

• 1. Thinking polio is eradicated – Polio is near eradication but still endemic in some countries.
• 2. Confusing the polio vaccines – IPV = killed; OPV = live, attenuated.
• 3. Thinking polio is transmitted by air – Polio is transmitted by the faecal-oral route.
• 4. Thinking polio only affects children – Polio can affect people of any age, but children are most vulnerable.
• 5. Thinking polio always causes paralysis – Most infections are asymptomatic.
• 6. Forgetting the role of physiotherapy – Physiotherapy is important for affected muscles.
• 7. Thinking there is an antiviral for polio – There is no antiviral therapy for polio.
• 8. Confusing the symptoms – Fever, headache, sore throat, stiff neck, paralysis.
• 9. Thinking polio is a bacterial disease – Polio is a viral disease.
• 10. Forgetting the global eradication efforts – WHO, CDC, UNICEF, Rotary, Gates Foundation.
• 11. Thinking OPV is safer than IPV – OPV has a rare risk of vaccine-associated paralytic polio; IPV has no such risk.
• 12. Confusing the serotypes – There are three serotypes: PV1, PV2, PV3.

Quick Revision

• Poliomyelitis is caused by polio virus which is also an enterovirus.
• Transmission: Polio virus is transmitted by the faecal oral route.
• Symptoms: It replicates in the oropharynx and intestinal tract and spread to blood and central nervous system where virus replicates in the motor neurone located in the spinal cord. Death of these cells results in paralysis of the muscles innervated by theses neuron. The motor nerve damage is permanent.
• Treatment: There is no antiviral therapy. Physiotherapy for the affected muscles is important.
• Prevention: Polio can be prevented by the killed (Salk vaccine, or injectable polio vaccine or IPV) and the live, attenuated (weakened) vaccine (sabin vaccine or, oral polio vaccine or OPV).

60-Second Revision

• Polio = viral disease
• Cause = poliovirus (enterovirus)
• Transmission = faecal-oral
• Replication = oropharynx, intestinal tract, blood, CNS, motor neurons
• **Symptoms** = paralysis
• Treatment = no antiviral; physiotherapy
• Prevention = IPV (Salk), OPV (Sabin)
• Motor nerve damage = permanent
• No cure = but preventable by vaccine
• Warning: Polio is transmitted by the faecal-oral route, not by air. Most infections are asymptomatic. Motor nerve damage is permanent. There is no antiviral therapy. IPV is killed; OPV is live, attenuated. OPV has a rare risk of vaccine-associated paralytic polio. Polio is near eradication but still endemic in some countries.