Poliovirus

Background

Microbiology

• Single-stranded, positive-sense, unenveloped RNA virus in the family Picornaviridae, genus Enterovirus, species Enterovirus C
• Currently, the most common cause of poliomyelitis is oral vaccine-derived poliovirus

Pathophysiology

• Targets the spinal anterior horn cells

Clinical Manifestations

• 90-95% of cases are clinically inapparent; 4-8% are abortive after the prodrome; and only 1-2% proceed to major illness
• Incubation period of 9 to 12 days (range 5 to 35 days) before onset of prodrome
• Minor illness lasts a few days
  • Fever, headache, sore throat, malaise, anorexia, vomiting, or abdominal pain
  • Normal neurological exam

Spinal Paralytic Poliomyelitis

• 0.1% of all poliovirus infection
• 2 to 5 days after resolution of minor illness, onset of aseptic meningitis, with fever, headache, nuchal rigidity, vomiting, and a CSF pleocytosis
• Weakness and paralysis start within a few days
  • Asymmetric, flaccid paralysis with increased DTRs
  • Typically proximal more than distal muscles, and legs more than arms
  • Typical pattern is one leg then one arm, or both legs then both arms
  • Progresses to complete paralysis over 2 to 3 days
• Rarely sensory loss; if present, consider another diagnosis such as Guillain-Barré syndrome

Bulbar Paralytic Poliomyelitis

• Represents 5 to 25% of paralytic poliomyelitis during outbreaks
• Affects the cranial nerves, presenting with dysphagia, nasal speech, and dyspnea
• Pooling saliva

Polioencephalitis

• Uncommon
• Presents like any other cause of encephalitis
• Confusion, altered level of consciousness, and seizure
• May have spastic paralysis rather than flaccid

Postpoliomyelitis Syndrome

• See post-polio syndrome
• Median latency 36 years after an episode of paralytic poliomyelitis
• New onset weakness, pain, atrophy, and fatigue
• Can affect the respiratory muscles

Differential Diagnosis

• Paralytic poliomyelitis: other causes of acute flaccid paralysis
  • Other enteroviruses, such as enterovirus A-71, enterovirus D-68
  • West Nile virus
  • Guillain-Barré syndrome, which would be symmetrical, bilateral ascending paralysis with loss of sensation, that progresses over 1 to 2 week and has minimal CSF pleocytosis with albuminocytologic dissociation
• Polioencephalitis: other causes of encephalitis

Diagnosis

• PCR is the only way to distinguish between wildtype polio and vaccine-derived
  • Throat swabs during the first week of illness
  • Feces for several weeks
  • CSF not particularly sensitive, but is helpful when positive and should still be sent
• Acute and convalescent serology

Management

• Supportive
• Can try pocapavir if available