What is polio and how is it prevented and managed?

Polio: Prevention and Management

Polio (poliomyelitis) is a highly infectious viral disease caused by three serotypes of poliovirus that primarily spreads through fecal-oral contact and can lead to irreversible paralysis, with vaccination being the only effective preventive measure.1, 2

Disease Characteristics

• Polio is caused by three serotypes of poliovirus (types 1,2, and 3) that are members of the enterovirus family, with type 1 most frequently causing paralytic disease in endemic countries, followed by type 3, and least frequently by type 2.2
• Transmission occurs primarily through direct fecal-oral contact, but can also spread through indirect contact with infectious saliva or feces, or by contaminated sewage or water.2
• The incubation period is typically 7-21 days (range: 4-30 days), with communicability lasting 4-6 weeks after infection.2, 1
• Humans are the only reservoir for poliovirus, with long-term carrier states being rare and reported only in immunodeficient persons.2

Clinical Presentation

• Most poliovirus infections (90-95%) are asymptomatic, while symptomatic cases typically manifest in two phases:1
  • Initial nonspecific febrile illness (first phase)
  • Aseptic meningitis or paralytic disease in a small percentage of cases (second phase)
• Paralytic polio occurs in approximately 0.1-1% of all poliovirus infections and is characterized by:1
  • Rapid progression to maximum paralysis within 2-4 days
  • Fever and muscle pain
  • Asymmetric spinal paralysis (more severe proximally than distally)
  • Absent or diminished deep tendon reflexes
  • Bulbar paralysis potentially affecting respiration and swallowing
• Paralytic polio is fatal in 2-10% of cases, with prognosis for recovery usually established within 6 months after onset.1

Post-Polio Syndrome

• After 30-40 years, 25-40% of persons who contracted paralytic polio during childhood may experience post-polio syndrome.1, 3
• Characterized by muscle pain, exacerbation of existing weakness, and development of new weakness or paralysis.1
• Risk factors include longer time since acute poliovirus infection, permanent residual impairment after recovery, and female gender.1, 2

Prevention

• Vaccination is the only effective preventive measure against polio, with current recommendations favoring the inactivated polio vaccine (IPV) over the oral polio vaccine (OPV) in developed countries.4, 5
• In the United States, poliovirus vaccines have successfully eliminated polio caused by wild poliovirus, with vaccination coverage among children aged 19-35 months exceeding 90% since 1996.2
• Two types of vaccines are available:5
  • Inactivated polio vaccine (IPV) developed by Salk - contains killed virus
  • Oral polio vaccine (OPV) developed by Sabin - contains live attenuated virus
• The shift from OPV to IPV in developed countries is due to the risk of vaccine-derived poliovirus (VDPV) associated with OPV.6, 4

Management

• No specific antiviral treatment exists for polio; management is primarily supportive:1, 7
  • Adequate rest during the acute phase
  • Pain management
  • Physical therapy to prevent contractures and deformities
  • Respiratory support if bulbar involvement occurs
  • Orthotic devices and assistive equipment for residual paralysis

Global Eradication Efforts

• The Global Polio Eradication Initiative has made significant progress since its launch in 1988:7, 8
  • The Americas, Pacific Rim, Europe, and central Asia appear to be polio-free
  • Wild poliovirus type 2 has not caused a case since 19998
  • Wild poliovirus type 3 has not caused a case since 20125
  • As of 2022, only three countries remained polio endemic: Nigeria, Pakistan, and Afghanistan7
• Challenges to eradication include:6, 4
  • Emergence of vaccine-derived polioviruses (VDPVs)
  • Low vaccination rates in some regions
  • Disruption of immunization programs due to factors like the COVID-19 pandemic

Diagnostic Considerations

• Laboratory confirmation is essential for diagnosis through:1
  • Virus isolation from stool, throat swabs, or cerebrospinal fluid
  • Serologic testing
• Polio can be misdiagnosed initially as other conditions like Guillain-Barré syndrome, polyneuritis, or transverse myelitis.1
• Electrodiagnostic studies help differentiate polio (an anterior horn cell disorder) from peripheral neuropathies.3

Pitfalls and Caveats

• Vaccine-derived polioviruses (VDPVs) pose a significant challenge to eradication efforts, with 1081 cases occurring in 2020 and 682 cases in 2021.6
• The risk of VDPV increases in areas with low vaccination coverage, highlighting the importance of maintaining high immunization rates.6
• Until worldwide polio eradication is achieved, importation of wild virus remains a possibility, necessitating continued vaccination of children early in their first year of life.2
• The United States reported its first case of poliomyelitis after 3 decades in July 2022, highlighting the ongoing threat.4