Poliovirus | Medical Science Optional Notes for UPSC PDF Download

Pathogenicity of Poliovirus

Modes of transmission-Feco-oral route/Inhalation/Conjunctival

Polio - Case Definition

• Suspect (based on history): Abrupt onset of weakness and flaccidity in any body part in a child below 15 years of age or paralysis in an individual of any age where polio is a potential concern.
• Probable (based on history and clinical examination): Cases that are epidemiologically linked.
• Confirmed (verified through laboratory tests): Identification of wild poliovirus isolation from stool samples.

Differential Diagnosis of Acute Flaccid Paralysis

(i) Poliomyelitis with paralysis
(ii) Guillain-Barre syndrome
(iii) Nerve inflammation due to trauma
(iv) Inflammation across the spinal cord
(v) Inflammation of the brain
(vi) Inflammation of the meninges
(vii) Other infections caused by enteroviruses (such as Coxsackie A, Coxsackie B, ECHO virus, Mumps virus, etc.)
(viii) Imbalances in metabolism (e.g., diabetes)
(ix) Exposure to toxins (lipid solvents, fish toxin, diphtheria toxin)
(x) Exposure to organophosphate pesticides, raw metals (such as lead)
(xi) Hereditary diseases (e.g., Charcot-Marie-Tooth)
(xii) Tumors.

Polio Virus - Clinical Manifestations

• 5-10 percent of the infected will develop clinical illness 
• IP 4 days to 4 weeks

Paralytic illness is more prevalent in older individuals, pregnant women, and those engaging in strenuous exercise or experiencing trauma when CNS symptoms occur. Tonsillectomy increases the susceptibility to bulbar poliomyelitis, and intramuscular injections heighten the risk of paralysis in the affected limb(s).

Post - Polio Syndrome

• The post-polio syndrome manifests as a new onset of weakness, fatigue, fasciculations, and pain, accompanied by additional atrophy in the muscle group affected during the initial paralytic disease 20-40 years earlier.
• This syndrome is more prevalent among women and becomes more common with the passage of time following the acute disease.
• The onset typically occurs insidiously, and weakness may occasionally extend to muscles that were not initially involved in the illness.
• The prognosis is generally favorable, with a slow progression to further weakness and intermittent plateau periods lasting 1-10 years.

The post-polio syndrome is believed to result from progressive dysfunction and loss of motor neurons compensating for those lost during the original infection, rather than persistent or reactivated poliovirus infection.

Lab Diagnosis of Polio Virus

Polio Status of India

The most recent instances of wild polio in India were documented in West Bengal and Gujarat on January 13, 2011. On March 27, 2014, the World Health Organization (WHO) declared India a polio-free country, as no cases of wild polio had been reported for three consecutive years.

Strategies for Polio Eradication

• Standard immunization: Implemented in accordance with the national Immunization Schedule.
• Additional immunization activities:
  • National Immunization Day (NID): Encompassing the entire country with oral poliovirus vaccine (OPV) (March 10, 2019).
  • Sub-National Immunization Day (SNID): Targeting specific states or portions of states.
  • Mop-up immunization: Concluding phase strategy when wild virus transmission is localized.
• Surveillance for acute flaccid paralysis (AFP): Conducted to pinpoint areas of wild poliovirus transmission and provide guidance for immunization initiatives accordingly.

Pulse Polio Immunization (PPI)

• A distinctive strategy for polio eradication is pulse polio immunization, where all children in the country receive oral poliovirus vaccine (OPV) simultaneously on a designated day, with a repeat dose administered after 4 to 6 weeks. This approach leads to the replacement of wild poliovirus strains with the harmless and protective OPV strain.
• The term "pulse" signifies the sudden and simultaneous mass administration of OPV to all children aged 0 to 5 years on a single day. To achieve effectiveness, a very high percentage of OPV coverage must be reached during each pulse. The Pulse Polio Immunization (PPI) program was initiated in India in 1995 with the objective of eradicating polio by the year 2000.

Steps taken by the Government to maintain polio free status in India

• Sustaining community immunity through annual high-quality National and Sub-National polio rounds.
• Maintaining an exceptionally high level of vigilance through nationwide surveillance to detect any importation or circulation of poliovirus and Vaccine-Derived Poliovirus (VDPV).
• Implementing environmental surveillance (sewage sampling) strategically in Mumbai, Delhi, Patna, Kolkata, Punjab, and Gujarat to identify poliovirus transmission and as a surrogate indicator for progress and programmatic interventions.
• Establishing Rapid Response Teams (RRT) in all States and Union Territories to promptly address any polio outbreak.
• Developing an Emergency Preparedness and Response Plan (EPRP) by all States, outlining steps to be taken in case of detecting a polio case.
• Mitigating the risk of importation from neighboring countries by offering continuous vaccination through teams at international borders with Pakistan, Bangladesh, Bhutan, Nepal, and Myanmar.
• Mandating polio vaccination for all international travelers departing from India to polio-affected countries, effective from March 1, 2014.
• Maintaining a rolling emergency stock of Oral Polio Vaccine (OPV) to respond to the detection or importation of Wild Poliovirus (WPV) or the emergence of circulating Vaccine-Derived Poliovirus (cVDPV).
• Recommending the introduction of Injectable Polio Vaccine (IPV) as an additional dose, along with the third dose of Diphtheria, Pertussis, and Tetanus (DPT) in the entire country, as advised by the National Technical Advisory Group on Immunization (NTAGI) in the last quarter of 2015, as part of the polio endgame strategy.

Types of Polio Vaccines

There are six distinct vaccines designed to halt polio transmission:

• Inactivated polio vaccine (IPV) - provides protection against poliovirus types 1, 2, and 3
• Trivalent oral polio vaccine (tOPV) - offers protection against poliovirus types 1, 2, and 3; note that tOPV is no longer in use following the "OPV Switch" in April 2016
• Bivalent oral polio vaccine (bOPV) - safeguards against poliovirus types 1 and 3
• Monovalent oral polio vaccines (mOPV1, mOPV2, and mOPV3) - each provides protection against an individual type of poliovirus, respectively

There are three variants of wild poliovirus (WPV): types 1, 2, and 3.
In September 2015, the eradication of WPV type 2 was officially declared.
As WPV type 3 has not been detected since November 2012, it is likely that WPV type 1 is the only remaining type of wild poliovirus in circulation.

The Polio Eradication and Endgame Strategy (WHO)

• In May 2012, the World Health Assembly declared the completion of polio eradication a programmatic emergency for global public health, leading to the development of the Polio Eradication and Endgame Strategic Plan 2013-2018, which was endorsed by the Strategic Advisory Group of Experts (SAGE) in November 2012.
• Objective 2 of the Eradication and Endgame Plan entails the introduction of at least one dose of inactivated poliomyelitis vaccine (IPV) into all routine immunization programs globally. Additionally, trivalent oral polio vaccines (tOPV) are to be replaced with bivalent oral polio vaccine (bOPV) in all OPV-using countries.
• The global "OPV Switch" was successfully executed worldwide in April 2016, setting the stage for the eventual withdrawal of all oral polio vaccines.
• India achieved a global milestone by becoming the first country to introduce fractional doses of IPV in its childhood immunization program across eight states and Union territories in early 2016.

Vaccine-associated paralytic polio (VAPP) and vaccine-derived poliovirus (VDPV)

• The utilization of oral polio vaccine (OPV), particularly in regions with low vaccination coverage, has been linked to the occurrence of vaccine-derived polio. This is attributed to mutations that lead to the restoration of viral fitness and neurovirulence during prolonged replication in individuals or through person-to-person transmission.
• Vaccine-associated paralytic polio (VAPP) is instigated by a strain of poliovirus that has undergone genetic changes in the intestine, deviating from the original attenuated vaccine strain found in OPV. It is associated with a single dose of OPV administered to a child or can manifest in a close, unvaccinated, or non-immune contact of the vaccine recipient who is excreting the mutated virus. Importantly, there is no risk of further transmission to others.

Vaccine-derived polioviruses (VDPVs) are characterized as live, attenuated strains of the virus contained in the oral polio vaccine (OPV) that have undergone changes and reverted to a form capable of causing paralysis in humans, demonstrating the potential for sustained circulation.

VDPVs exhibit differences from the original Sabin strains found in the vaccine, ranging from 1 to 15 percent of VP1 nucleotides. The assessment of genetic alterations serves as a means to monitor virus circulation.

Circulating vaccine-derived polioviruses (cVDPVs) are linked to sustained person-to-person transmission and are acknowledged to be circulating in the environment. The term "persistent cVDPVs" pertains to cVDPVs documented to have circulated for more than six months.

Immunodeficiency-related vaccine-derived polioviruses (iVDPVs) are isolated from immunodeficient patients experiencing prolonged infections after exposure to OPV. Notably, iVDPVs have not been observed to transmit or spread to others.

Ambiguous vaccine-derived polioviruses (aVDPVs) are isolated from a single immunocompetent Acute Flaccid Paralysis (AFP) or paralytic poliomyelitis patient, with or without additional isolates from contacts, or from healthy individuals or the environment in the absence of paralytic cases.

AFP Surveillance

Definition: Acute flaccid paralysis is characterized by the sudden onset of weakness and floppiness in any part of the body in a child under 15 years of age or paralysis in an individual of any age where polio is suspected.

The aim of Acute Flaccid Paralysis (AFP) surveillance is to eliminate polio infection as a potential cause in as many AFP cases as possible. It involves testing stool specimens from all AFP cases soon after the onset of paralysis, as sensitivity increases with a higher number of investigated AFP cases.

All cases of acute flaccid paralysis, as per the existing case definition, should be reported within six months of the onset of symptoms.

For an adequate stool sample, two samples, each at least 8 grams (approximately the size of an adult thumb), should be collected within 14 days of the onset of paralysis. The samples should have a minimum interval of 24 to 48 hours between collections. These samples must reach a WHO-accredited laboratory in good condition, meaning no leakage, desiccation, with proper documentation, and maintaining a proper reverse cold chain.

The term "reverse cold chain" refers to a system that ensures the proper storage and transportation of samples at recommended temperatures from the point of collection to the laboratory, akin to the role of maintaining vaccine potency in the cold chain.

AFP Surveillance-Flow Chart

Duties & Responsibilities of Community Health Order (CHO)
Surveillance Medical Officer (SMO)