Polio

Basics

Vaccine-preventable disease caused by highly infectious poliovirus
Infected individuals are usually asymptomatic, but can present with symptoms ranging from flu-like illness to acute flaccid paralysis or meningitis
Incubation period 3–6 d for nonparalytic infection and 7–21 d for the onset of paralytic polio
Clinical manifestations:
- Subclinical (ie, not apparent) 90–95%
- Abortive poliomyelitis 4–8%:
  - Clinically indistinct from many other viral infections (fever, myalgias, malaise)
  - Only suspected to be polio during an epidemic
- Nonparalytic poliomyelitis 1–2%:
  - Differs from abortive poliomyelitis by the presence of meningeal irritation
  - Course similar to any aseptic meningitis
- Paralytic poliomyelitis 0.1%, which is further subdivided:
  - Spinal paralytic poliomyelitis (frank polio)
  - Bulbar paralytic poliomyelitis (10% of paralytic polio): Paralysis of muscle groups innervated by cranial nerves; involves the circulatory and respiratory centers of the medulla with high mortality
  - Mixed bulbospinal poliomyelitis
- Postpoliomyelitis syndrome:
  - New onset of increased muscle weakness, pain, and focal or generalized atrophy
  - Usually occurs over 15 yr after active illness, often in the previously affected limb
  - Risk factors include age at time of infection, extent of recovery and female sex (increased risk with better recovery)
  - Gradual progression

Polioviruses:
- Small, nonenveloped RNA viruses of the enterovirus genera
- 3 strains of wild poliovirus: 1, 2, 3
  - Types 2 and 3 are eradicated; type 1 endemic only to Pakistan and Afghanistan
Humans are the only natural host and reservoir
Fecal–oral or oral–oral transmission:
- Oral polio vaccine:
  - Contains a weakened version of virus excreted by vaccinated person for weeks
  - Contacts can become inoculated and gain immunity through secondary exposure
  - In very rare instances, however, the vaccinated person or an unvaccinated person around them can become infected from the neurovirulent conversion of vaccine virus
  - To avoid vaccine-associated paralytic poliomyelitis (VAP) the US has only used intramuscular inactivated polio virus (IPV) since 2000
  - Global decrease in VAP incidence since the worldwide introduction of IPV in 2016
  - IPV is costly, however, so OPV is still used during outbreaks and in endemic areas

There's more to see -- the rest of this topic is available only to subscribers.

All content is protected by copyright and may not be used for AI model training or other unauthorized purposes.