Define Poliomyelitis & Polio Eradication. Describe its clinical features, pathogenesis, types and diagnosis.

Definition

• Poliomyelitis is an acute viral infection caused by the poliovirus (an enterovirus, types 1–3), spread by the faeco-oral route.
• It can damage anterior horn cells of the spinal cord, causing acute flaccid paralysis (AFP).

Clinical Features

• Most infections are asymptomatic/minor (fever, sore throat).
• Paralytic polio — asymmetric, flaccid, lower-motor-neuron paralysis with intact sensation; may involve respiratory/bulbar muscles.
• Residual weakness/deformity in survivors; post-polio syndrome later.

Opv VS Ipv

Polio Eradication Strategy

• High routine immunisation coverage plus supplementary Pulse Polio (National Immunisation Days).
• Acute flaccid paralysis (AFP) surveillance — investigate every case of AFP in children under 15 (stool for poliovirus) to detect any wild/vaccine-derived virus.
• The 'endgame' switch — from trivalent to bivalent OPV and introduction of IPV to withdraw live virus safely.

Vaccine-associated Risks

• VAPP — vaccine-associated paralytic polio (very rare, from the live OPV strain).
• VDPV — vaccine-derived polioviruses that can regain neurovirulence/circulate in under-immunised populations — a reason for the eventual switch to IPV.

Pathogenesis

The virus multiplies in the pharynx and gut, then may spread to the CNS and destroy the anterior horn cells of the spinal cord (and sometimes brainstem), producing lower-motor-neuron paralysis with intact sensation.

Clinical Types

• Spinal — asymmetric limb weakness (commonest paralytic form).
• Bulbar — cranial nerve/respiratory involvement (dangerous); bulbospinal.

Differential Diagnosis of Afp

• Guillain-Barré syndrome (symmetric, areflexia, sensory), transverse myelitis (sensory level, sphincter involvement), traumatic neuritis.
• All AFP is investigated to exclude poliovirus.

Post-polio Syndrome

Years after acute paralytic polio, some survivors develop new muscle weakness, fatigue and pain (post-polio syndrome) in previously affected or unaffected muscles; management is supportive.

Global & National Status

• Global eradication is close — wild poliovirus remains in very few countries; type 2 and type 3 wild virus have been certified eradicated.
• India's success (polio-free 2014) rests on sustained surveillance and immunisation to prevent re-importation.

Prevention & Control Summary

• High routine OPV/IPV coverage, Pulse Polio supplementary immunisation, strong AFP surveillance, and environmental (sewage) surveillance.
• Maintaining these prevents re-importation now that India is polio-free.

Opv VS Ipv — Summary of the 'endgame'

• The eradication endgame reduces reliance on live OPV (which carries rare VAPP/VDPV risk) by introducing IPV and switching OPV formulations.
• IPV provides individual humoral protection safely; OPV's gut immunity and herd effect remain valuable during transition.

Significance of Afp Surveillance

Sensitive AFP surveillance — investigating every case of acute flaccid paralysis in children under 15 with stool testing — is the backbone of certifying and maintaining polio-free status, ensuring that any wild or vaccine-derived poliovirus is detected and contained promptly.

WHY the Endgame Requires Both Vaccines

• Understanding why the world's polio endgame strategy uses OPV and IPV together, and then plans to withdraw OPV entirely, follows directly.
• As wild poliovirus disappears, the paradox emerges: eventually the only polio left in the world will be that caused BY the vaccine (VAPP and cVDPV).
• At that point OPV becomes a liability.
• But it cannot simply be stopped, because populations would lose their gut immunity.
• The strategy is therefore staged: first, the type-2 component (which caused most cVDPV cases) was withdrawn globally in 2016 — the 'switch' from trivalent to bivalent OPV.
• Second, at least one dose of injectable IPV was introduced into routine schedules everywhere (India uses fractional IPV, fIPV, given intradermally — which is dose-sparing and cheaper), to maintain protection against type 2 and to provide safe individual immunity.
• Finally, once transmission has ceased everywhere, OPV will be withdrawn entirely and the world will use IPV alone.
• Meanwhile, India remains polio-free (certified 2014) only through continued vigilance: AFP surveillance, high routine coverage, and Pulse Polio campaigns.