About the Disease
Discover – Poliomyelitis Lecture Notes for Medical Undergraduates – Poliomyelitis (polio) is a highly infectious viral disease that primarily affects children under 5 years of age. It is transmitted mainly through the faecal-oral route and multiplies in the intestine, from where it can invade the nervous system and cause paralysis. The deficit is purely motor, with sensation intact.
Transmission
• Person-to-person spread via faecal-oral route.
• Contaminated water or food.
• Virus multiplies in the intestine and can lead to paralysis.
Mnemonic: F-W-C (Faecal-oral, Water, Contaminated food)
Epidemiology
Source: WHO. Endemic Countries: Pakistan and Afghanistan
About the Virus
• Three serotypes: Type 1, Type 2, Type 3.
• Immunity to one serotype does not confer immunity to the others.
• Type 2 eradicated in 2015, last seen in India in 1999.
• Type 3 eradicated in 2019, last seen in 2012.
• Only Type 1 still circulates today, primarily in two countries.
• Global polio incidence has decreased by 99%.
Vaccine-Associated Paralytic Poliomyelitis (VAPP)
• Caused by loss of viral attenuation in OPV.
• Extremely rare
• Linked to serotype 3, more common in immunodeficient patients.
Mnemonic: R-S-I (Rare, Serotype 3, Immunodeficient)
Circulating Vaccine-Derived Poliovirus (cVDPV)
• OPV virus can spread in areas with poor sanitation and offer passive immunization.
• In under-immunized populations, excreted virus can circulate for an extended time, undergo genetic changes, and mutate into a form that can cause paralysis.
• cVDPV takes at least 12 months to emerge in under-immunized populations.
• Low vaccination coverage is the main problem, not the vaccine itself.
• Solution: 2-3 rounds of high-quality immunization campaigns to stop the virus.
Mnemonic: I-P-G-M (Immunodeficient, Prolonged circulation, Genetic mutation, Mutated virus causing paralysis)
Diagnosis
• Tests include blood, cerebrospinal fluid (CSF), respiratory, and stool viral cultures, as well as PCR to detect poliovirus.
Mnemonic: B-C-R-S-P (Blood cultures, CSF, Respiratory cultures, Stool cultures, PCR)
Complications
• Major complications: Paralysis with bulbar involvement, fatal respiratory and cardiovascular collapse, and postpolio syndrome.
• Postpolio syndrome: New-onset or progressive muscle weakness in previously diagnosed polio patients.
Mnemonic: P-R-P (Paralysis, Respiratory collapse, Postpolio syndrome)
Prevention of Polio
- Routine Immunization
- Supplementary Immunization
- Surveillance
- Targeted “Mop-Up” Campaigns
AFP Surveillance: 4 steps
1. Finding and Reporting AFP cases: Detect at least 1 case of AFP per 100,000 children under 15 years of age.
2. Transporting Stool Samples: Samples should arrive at the lab within 72 hours, with two specimens collected 24 hours apart and arriving via reverse cold chain.
3. Isolating Poliovirus: Distinguish between wild and vaccine-related poliovirus.
4. Mapping the Virus: Map the genetic makeup and geographical areas of circulation.
• Note: 80% of AFP cases should have a follow-up examination at 60 days after onset of paralysis.
Mnemonic: F-T-I-M (Finding, Transporting, Isolating, Mapping)
Polio Eradication Strategy 2022–2026 strategic framework: Source WHO
Tip: Remember the vision and goals.
Current Challenges
• Afghanistan: Ban on house-to-house immunization has led to over 1 million children being missed, with 90% of WPV1 cases in inaccessible areas.
• Poor-quality campaigns due to insufficient planning, staffing issues, and lack of accountability.
• Pakistan: Progress stalled due to complacency, leadership transitions, vaccine hesitancy, and misinformation on social media.
• Marginalized Pashto-speaking communities disproportionately affected (81% of WPV cases).
Mnemonic: M-P-L-V (Missed children, Poor campaigns, Leadership issues, Vulnerable communities)
Sources:
- www.who.int
- www.polioeradication.org
Practice Questions
Multiple Choice Questions (MCQs)
- What is the primary mode of transmission for poliomyelitis?
- a) Airborne droplets
- b) Blood transfusion
- c) Faecal-oral route
- d) Skin contact
- Which serotype of poliovirus remains in circulation today?
- a) Type 1
- b) Type 2
- c) Type 3
- d) All three
- Vaccine-associated paralytic poliomyelitis (VAPP) is most commonly associated with which serotype?
- a) Type 1
- b) Type 2
- c) Type 3
- d) Type 4
- What is the characteristic feature of paralysis in poliomyelitis?
- a) Sensory loss
- b) Motor deficit with sensory intact
- c) Complete paralysis of all limbs
- d) Sensory and motor deficit
- Which diagnostic test is most specific for detecting poliovirus?
- a) Blood viral culture
- b) CSF viral culture
- c) Stool viral culture
- d) PCR
- Which year was Type 2 wild poliovirus declared eradicated?
- a) 2012
- b) 2015
- c) 1999
- d) 2019
- What is the minimum number of AFP cases per 100,000 children under 15 that a surveillance system should detect?
- a) 1
- b) 5
- c) 10
- d) 50
- What is the primary cause of circulating vaccine-derived poliovirus (cVDPV)?
- a) Poor vaccine quality
- b) Prolonged circulation of excreted vaccine virus in under-immunized populations
- c) Lack of wild poliovirus
- d) Transmission via mosquitoes
- Which of the following is NOT a complication of poliomyelitis?
- a) Respiratory collapse
- b) Paralysis with bulbar involvement
- c) Myocarditis
- d) Postpolio syndrome
- Which of the following factors does NOT contribute to vaccine hesitancy in Pakistan?
- a) Misinformation on social media
- b) Leadership transitions
- c) Widespread knowledge about vaccines
- d) Complacency after declining cases
- How many stool specimens are needed for adequate analysis in AFP surveillance?
- a) 1
- b) 2
- c) 3
- d) 5
- How long does it typically take for cVDPV to develop in an under-immunized population?
- a) 1-6 months
- b) 6-12 months
- c) 12-18 months
- d) 18-24 months
- Which of the following countries still has circulating wild poliovirus?
- a) India
- b) Afghanistan
- c) Nigeria
- d) Brazil
- Which of the following is the recommended method for stopping cVDPV outbreaks?
- a) Two doses of inactivated polio vaccine (IPV)
- b) 2-3 rounds of high-quality oral polio vaccine (OPV) immunization campaigns
- c) Mass vaccination with measles vaccine
- d) Isolation of infected individuals
- Which factor is the primary issue causing cVDPV outbreaks?
- a) Faulty vaccines
- b) Low vaccination coverage
- c) Over-vaccination
- d) Rapid spread of wild poliovirus
- What is the minimum follow-up period for AFP cases after onset of paralysis?
- a) 15 days
- b) 30 days
- c) 45 days
- d) 60 days
- Which season is poliovirus most commonly associated with?
- a) Winter
- b) Summer
- c) Rainy season
- d) Spring
- Which diagnostic tool is crucial to differentiate poliovirus from other viral causes of paralysis?
- a) MRI
- b) Blood viral cultures
- c) PCR
- d) CSF analysis
- Which of the following is NOT a recommended practice to improve immunization coverage in polio-endemic areas?
- a) Using IPV instead of OPV
- b) Removing Type 2 from OPV formulation
- c) House-to-house immunization campaigns
- d) Discontinuing OPV altogether
- Which polio strain was last detected in November 2012?
- a) Type 1
- b) Type 2
- c) Type 3
- d) Vaccine-derived strain
- Which complication is characterized by new muscle weakness after recovery from poliomyelitis?
- a) Guillain-Barré syndrome
- b) Postpolio syndrome
- c) Transverse myelitis
- d) Myasthenia gravis
- In which country was Type 2 wild poliovirus last detected?
- a) Afghanistan
- b) Pakistan
- c) India
- d) Nigeria
- Which population in Pakistan is disproportionately affected by wild poliovirus?
- a) Urdu-speaking
- b) Pashto-speaking
- c) Bengali-speaking
- d) English-speaking
- What is the ultimate solution to all polio outbreaks?
- a) Enhanced sanitation measures
- b) High-quality OPV immunization campaigns
- c) Quarantine of affected individuals
- d) Administration of antibiotics
- What is the recommended time frame for collecting stool samples after the onset of paralysis?
- a) 7 days
- b) 10 days
- c) 14 days
- d) 21 days
Answers to MCQs
- c) Faecal-oral route
- a) Type 1
- c) Type 3
- b) Motor deficit with sensory intact
- d) PCR
- b) 2015
- a) 1
- b) Prolonged circulation of excreted vaccine virus in under-immunized populations
- c) Myocarditis
- c) Widespread knowledge about vaccines
- b) 2
- c) 12-18 months
- b) Afghanistan
- b) 2-3 rounds of high-quality oral polio vaccine (OPV) immunization campaigns
- b) Low vaccination coverage
- d) 60 days
- c) Rainy season
- c) PCR
- d) Discontinuing OPV altogether
- c) Type 3
- b) Postpolio syndrome
- c) India
- b) Pashto-speaking
- b) High-quality OPV immunization campaigns
- c) 14 days
Subjective Practice Questions
- Explain the pathophysiology of poliomyelitis and how it leads to paralysis.
- Hint: Discuss how the poliovirus infects the human body, multiplies in the intestines, invades the nervous system, and leads to motor paralysis. Mention pure motor deficit and the role of faecal-oral transmission.
- Points to cover: Virus replication, invasion of the nervous system, motor deficit.
- Describe the development of circulating vaccine-derived poliovirus (cVDPV) and its contributing factors.
- Hint: Cover how cVDPV develops due to low vaccination coverage, genetic mutations in the vaccine virus, and how it can cause paralysis like the wild virus.
- Points to cover: Role of OPV, low vaccination coverage, genetic changes, prevention methods.
- Discuss the major challenges faced by Afghanistan and Pakistan in eradicating polio.
- Hint: Mention issues like house-to-house immunization bans, poor-quality campaigns, vaccine hesitancy, and misinformation on social media.
- Points to cover: Immunization bans, vaccine hesitancy, marginalized populations, and operational challenges.
- How is Acute Flaccid Paralysis (AFP) surveillance conducted, and why is it important for polio eradication?
- Hint: Outline the four steps of AFP surveillance, including finding cases, stool sample collection, virus isolation, and virus mapping. Emphasize its role in monitoring poliovirus circulation.
- Points to cover: AFP detection, sample transport, poliovirus isolation, and surveillance effectiveness.
- Compare and contrast Vaccine-Associated Paralytic Poliomyelitis (VAPP) and wild poliovirus infection in terms of pathogenesis and epidemiology.
- Hint: Focus on the differences in origin (vaccine vs. wild), how VAPP is rare and more associated with serotype 3, while wild poliovirus affects unvaccinated populations.
- Points to cover: Pathogenesis, serotypes involved, immunization coverage, and rarity of VAPP.
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