Polio, medically known as poliomyelitis, is a highly contagious viral disease caused by the poliovirus.

Once a global health menace, polio primarily affects young children and can result in paralysis, permanent disability, or even death.

Transmission and Pathogenesis

The poliovirus is transmitted mainly via the fecal-oral route, making poor sanitation and hygiene significant factors in its spread. After entering the body through the mouth, the virus multiplies in the intestinal tract and can then enter the bloodstream. In most cases, infection is asymptomatic or mild, with common symptoms including fever, fatigue, headache, stiffness, and limb pain lasting from a few days to a week. However, in approximately 1% of infections, the virus breaches the central nervous system, attacking motor neurons responsible for muscle control.

This neuroinvasion leads to acute flaccid paralysis, often rapidly progressing and most commonly affecting the legs. The paralysis can be permanent, and respiratory muscles may also be compromised, resulting in life-threatening complications. The poliovirus can be shed in stool for several weeks, further facilitating its transmission in communities lacking adequate sanitation.

Clinical Presentation

The spectrum of polio infection ranges from subclinical cases to severe paralytic disease. Non-paralytic polio presents with symptoms resembling a mild viral illness such as sore throat, fever, and neck stiffness. Paralytic polio, the most feared manifestation, causes sudden onset of muscle weakness and loss of reflexes. Recovered patients may later develop post-polio syndrome, characterized by progressive muscle weakness and fatigue decades after the original infection. This highlights the virus's lasting impact beyond acute illness.

Prevention Strategies

No curative treatment exists for polio, underscoring the essential role of prevention through immunization. The polio vaccine (OPV) and inactivated polio vaccine (IPV) are critical tools in global eradication efforts. Vaccines stimulate protective immunity, reducing viral replication and preventing paralytic disease. Repeated administration is necessary to confer lifelong protection. Alongside vaccination, improvements in water, sanitation, and hygiene (WASH) infrastructure are pivotal in limiting viral spread.

Global Eradication Efforts and Ongoing Challenges

Since the launch of the Global Polio Eradication Initiative in 1988, over 20 million cases of paralysis have been prevented. However, polio remains endemic in a few regions with low immunization coverage, posing risks of outbreaks. Recent detections of poliovirus in wastewater and isolated cases emphasize the need to sustain high vaccination rates and robust surveillance. Public health measures such as community engagement, targeted vaccination campaigns, and infrastructure development continue to be essential.

According to Dr. Gloria Rey, a polio expert and Regional Advisor at PAHO, if the weakened live poliovirus can circulate in populations with low vaccination coverage, it can mutate and revert to a form that causes illness and paralysis. This highlights the importance of maintaining high vaccine coverage across all countries.

Polio is a contagious viral illness with the potential to cause severe neurological damage. Transmission occurs primarily through contaminated food and water, facilitating rapid spread in unsanitary environments. While most infections are asymptomatic, the minority that progress to paralytic disease face lifelong disability or death. Vaccination remains the cornerstone of prevention, effectively shielding populations and paving the way toward global eradication.