Polio Stages: From Infection to Paralysis – Symptoms and Progression

Poliomyelitis, caused by poliovirus (enterovirus), progresses through distinct stages. Most infections are asymptomatic; paralysis occurs in a minority.

Stage 1: Incubation Period

• Duration: 3–35 days (average 7–10 days)
• Viral replication in oropharynx and gut; fecal-oral shedding begins
• No symptoms; person is infectious

Stage 2: Abortive Poliomyelitis (Minor Illness)

• ~24% of infections
• Symptoms: low-grade fever, sore throat, headache, malaise, nausea, vomiting, abdominal pain
• Duration: 2–3 days; full recovery, no CNS involvement

Stage 3: Non-Paralytic Aseptic Meningitis

• ~1–5% of infections
• Symptoms: abortive symptoms + neck/back stiffness, photophobia, Kernig/Brudzinski signs
• CSF: lymphocytic pleocytosis, elevated protein, normal glucose
• Recovery: days to weeks; no permanent paralysis

Stage 4: Paralytic Poliomyelitis

• <1% of infections (1 in 200–2000)
• Virus invades CNS → destroys anterior horn motor neurons
• Types:
  • Spinal (79%): asymmetric flaccid paralysis, proximal > distal, legs > arms
  • Bulbar (2%): cranial nerve involvement → dysphagia, dysphonia, respiratory failure
  • Bulbospinal (19%): combined
• Acute phase: fever, severe myalgia, fasciculations → flaccid weakness → atrophy
• Recovery: maximal at 6 months; residual paralysis in ~2/3 of paralytic cases
• Complications: respiratory failure, post-polio syndrome (decades later)

Eradication Status

Wild poliovirus types 2 and 3 eradicated; type 1 endemic only in Afghanistan/Pakistan (2024). Vaccine-derived poliovirus (cVDPV) outbreaks occur in under-immunized communities. IPV/OPV vaccination remains critical.