- Poliovirus is a highly infectious enterovirus belonging to the Picornaviridae family. It is a small, non-enveloped virus containing single-stranded RNA as its genetic material. There are three serotypes of wild poliovirus (types 1, 2, and 3), though type 2 was declared eradicated in 2015 and type 3 in 2019.
- The virus primarily spreads through the fecal-oral route, particularly in areas with poor sanitation. It can also transmit through contaminated water or food. Once ingested, the virus multiplies in the intestines before potentially entering the bloodstream and nervous system. Most infected individuals (around 72%) remain asymptomatic, while about 25% experience mild symptoms similar to flu.
- In a small percentage of cases (less than 1%), the virus invades the central nervous system, leading to muscle weakness and paralysis, typically in the legs. This condition, known as paralytic poliomyelitis, can result in permanent disability. In severe cases affecting the respiratory muscles, it can be life-threatening without mechanical ventilation support.
- Post-polio syndrome is a condition that can affect polio survivors decades after their initial infection. It involves progressive muscle weakness, fatigue, and pain in previously affected and unaffected muscles. The exact cause remains unclear, but it’s believed to relate to the aging of motor neurons that survived the initial infection.
- The development of effective vaccines in the 1950s and 1960s – both the Salk inactivated polio vaccine (IPV) and Sabin oral polio vaccine (OPV) – led to dramatic reductions in polio cases worldwide. The Global Polio Eradication Initiative, launched in 1988, has reduced polio cases by 99.9%, with wild poliovirus remaining endemic in only a few regions globally.
- Polio eradication efforts face challenges including vaccine hesitancy, political instability in endemic regions, and the emergence of vaccine-derived poliovirus strains. These strains can develop when the weakened live virus in the oral vaccine mutates and regains its ability to cause paralysis in under-immunized populations.
