Poliomyelitis, or polio, is a severe disease that has historically left a significant mark on human health, particularly affecting young children. This highly infectious viral illness can lead to permanent disability and even death. Its widespread impact highlighted the urgent need for effective prevention. The development and widespread use of vaccines have drastically altered the trajectory of this disease, offering powerful protection.
Understanding Poliomyelitis
Poliomyelitis is a highly infectious viral disease caused by the poliovirus, which belongs to the enterovirus group. The virus primarily targets the nervous system, which can result in paralysis. There are three distinct types of wild poliovirus: WPV1, WPV2, and WPV3. While all three types can cause identical symptoms, each must be eradicated individually. Wild poliovirus type 2 was declared eradicated in 2015, and type 3 in 2019; only wild poliovirus type 1 remains in circulation.
How Poliomyelitis Affects the Body
The poliovirus primarily spreads through the fecal-oral route, via contaminated food, water, or objects. Less commonly, it can also spread through infectious respiratory droplets when an infected person coughs or sneezes. The virus enters the body through the mouth and initially multiplies in the intestines. From there, it can invade the nervous system, leading to varying degrees of illness. The incubation period for polio typically ranges from 7 to 14 days.
Most people infected with the poliovirus experience no visible symptoms and are asymptomatic carriers. These individuals can still spread the virus without realizing they are infected. Another form, abortive polio, presents with mild, flu-like symptoms such as fever, headache, muscle aches, sore throat, and gastrointestinal discomfort, usually lasting 2 to 3 days.
Non-paralytic polio, a more severe form, involves aseptic meningitis, characterized by symptoms like a stiff neck and back, muscle pain, and sensitivity to light. While these symptoms are more pronounced, they do not lead to paralysis. The most severe manifestation is paralytic polio, which is rare. This form progresses to intense pain, extreme touch sensitivity, muscle spasms or twitching, and rapidly developing muscle weakness that can lead to limp paralysis, often affecting the lower limbs. In some instances, it can involve the muscles needed for breathing or swallowing, potentially causing respiratory failure and death.
Managing Poliomyelitis and Preventing Infection
There is currently no cure for poliomyelitis; treatment focuses on supportive care. This includes managing pain, providing physical therapy for muscle function and mobility, and offering respiratory support when breathing muscles are affected. Rehabilitation efforts, such as physiotherapy, strength training, and the use of mobility aids, are important for long-term patients to adapt and improve their quality of life.
Prevention through vaccination remains the most effective strategy against polio. Two main types of polio vaccines are used globally: the Inactivated Poliovirus Vaccine (IPV) and the Oral Poliovirus Vaccine (OPV). IPV contains killed poliovirus strains and is given by injection, protecting against all three poliovirus types. It is recommended for children in the United States as part of routine immunizations, usually administered in four doses at 2 months, 4 months, 6 through 18 months, and 4 through 6 years of age. The minimum interval between the first two doses and the second and third doses is 4 weeks, with a 6-month minimum between the third and fourth doses.
OPV contains weakened, live poliovirus strains and is administered orally. While trivalent OPV is no longer in global use, bivalent OPV and monovalent OPVs are still utilized in various countries. The choice between IPV and OPV, or a combination, depends on local conditions to ensure the best protection. Consistent and high vaccination coverage is necessary to prevent outbreaks and stop virus transmission.
The Global Fight Against Poliomyelitis
The Global Polio Eradication Initiative (GPEI) was launched in 1988 with the goal of eradicating polio worldwide. Since its inception, the GPEI has achieved a significant reduction in polio cases, decreasing them by over 99%. This remarkable progress has brought the world to the brink of eradicating a human disease for only the second time in history, following smallpox.
Despite these achievements, wild poliovirus type 1 (WPV1) remains endemic in only two countries: Afghanistan and Pakistan. Challenges to complete eradication persist, including vaccine hesitancy, difficulties in reaching children in conflict zones, and the emergence of circulating vaccine-derived poliovirus (cVDPV). CVDPV can arise when the weakened virus in OPV circulates in under-immunized populations, mutating and regaining its ability to cause paralysis and spread. Continued global surveillance and sustained vaccination efforts are essential to prevent the re-emergence of polio and ensure a truly polio-free world.