Etiology
Poliomyelitis is caused by wild poliovirus type 1 (wild poliovirus types 2 and 3 have been eradicated) and by type 2 circulating vaccine derived poliovirus (cVDPV), which is currently causing vaccine-derived polio outbreaks in countries where polio vaccination coverage has decreased during recent years.
World Health Organization: poliomyelitis
Opens in new window Poliovirus is an RNA virus that is a type of enterovirus.[21] Wild poliovirus type 2 was certified as eradicated in September 2015 and wild poliovirus type 3 was certified eradicated in October 2019.[22][Figure caption and citation for the preceding image starts]: Wild poliovirusWHO public image library for polio (www.polioeradication.org) [Citation ends].
VDPV arises from oral attenuated poliovirus vaccine (OPV). The attenuated virus replicates in the intestine stimulating an immune response; however, over time it can mutate and cause disease just as wild poliovirus does.[23]
Pathophysiology
Poliovirus is transmitted via the fecal-oral route, particularly in low-hygiene settings. There is no nonhuman reservoir. The incubation period varies from 3 days to 30 days, and the virus can be excreted from the gastrointestinal tract for up to 6 weeks. The virus replicates in the nasopharynx and GI tract, and may spread via the bloodstream to the lymph nodes and, rarely, to the central nervous system, where it affects the motor neurons in the anterior horn and brainstem. It is the destruction of motor neurons that leads to the development of acute flaccid paralysis (AFP).[1]
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