Poliomyelitis

Poliomyelitis is an infection by poliovirus that is usually asymptomatic or mild but can invade the nervous system and cause acute flaccid paralysis. It has been the target of a global eradication effort built on inactivated and oral polio vaccines, making it a defining example of a vaccine-preventable disease (Minor, 2012).

Definition

Poliomyelitis is an enteroviral infection by poliovirus, transmitted mainly by the faecal-oral route, that is frequently asymptomatic but can cause acute flaccid paralysis through damage to motor neurons, and is preventable by inactivated or oral polio vaccines.

Scope

This topic covers poliomyelitis as a clinical and public-health entity: the poliovirus and its spread, the spectrum from inapparent infection to paralytic disease, the two vaccine types and their roles, and the epidemiology of eradication including vaccine-derived poliovirus. It is a reference overview and does not provide treatment or prescribing guidance.

Core questions

• How does poliovirus spread and cause paralysis in a minority of those infected?
• How do inactivated and oral polio vaccines differ in their effects?
• What is vaccine-derived poliovirus and why does it matter for eradication?
• Why has polio been a target for global eradication?

Key concepts

• Poliovirus (Enterovirus, Picornaviridae)
• Faecal-oral transmission
• Asymptomatic and abortive infection
• Acute flaccid paralysis
• Inactivated poliovirus vaccine (IPV)
• Oral poliovirus vaccine (OPV)
• Vaccine-derived poliovirus
• Global eradication

Mechanisms

Poliovirus is acquired mainly by the faecal-oral route, replicates in the gut, and in most people causes no or minor illness. In a small fraction it reaches the central nervous system and damages motor neurons in the spinal cord, producing acute flaccid paralysis. Two vaccine approaches confer protection: inactivated poliovirus vaccine, which induces systemic immunity, and live attenuated oral poliovirus vaccine, which also induces intestinal immunity and can spread to contacts but can, rarely, revert and circulate as vaccine-derived poliovirus (Minor, 2012; Bandyopadhyay et al., 2018). The choice and sequencing of these vaccines is central to the eradication endgame.

Clinical relevance

Poliomyelitis illustrates how a mostly silent infection can occasionally cause permanent paralysis, and how vaccine choice shapes both individual and population protection in an eradication programme. This entry is descriptive and educational; it characterises the disease and its prevention and is not a basis for diagnosis or treatment in an individual patient.

Epidemiology

Poliomyelitis was once a feared cause of childhood paralysis worldwide; vaccination drove wild poliovirus to the brink of eradication, with transmission of some serotypes interrupted globally (Minor, 2012). As wild virus has receded, vaccine-derived poliovirus from oral vaccine has become a comparatively more prominent source of paralytic cases, shaping current eradication strategy (Bandyopadhyay et al., 2018).

History

Epidemic poliomyelitis became a major cause of childhood paralysis in the first half of the twentieth century. The development of an inactivated vaccine by Jonas Salk and a live oral vaccine by Albert Sabin transformed the disease, and a global eradication initiative subsequently reduced wild poliovirus to a few remaining reservoirs while raising new questions about vaccine-derived virus (Minor, 2012; Bandyopadhyay et al., 2018).

Debates

How should oral and inactivated vaccines be used in the eradication endgame?

Oral vaccine provides strong intestinal immunity but can seed vaccine-derived poliovirus, while inactivated vaccine does not; balancing their roles to finish eradication without new outbreaks is a central strategic question.

Key figures

• Jonas Salk
• Albert Sabin
• Philip D. Minor

Seminal works

• minor-2012
• bandyopadhyay-2018

Frequently asked questions

Why does only a small number of polio infections cause paralysis?

Most poliovirus infections are asymptomatic or cause only mild illness. Paralysis occurs in a small minority when the virus reaches and damages motor neurons in the spinal cord.

What is vaccine-derived poliovirus?

The live attenuated virus in oral polio vaccine can, rarely, revert toward a form that regains the ability to cause paralysis and circulate in undervaccinated communities. Managing this risk is a key consideration in the strategy to eradicate polio.