Human enteroviruses and the long road to acute flacid paralysis eradication

Enteroviruses (EVs) are a highly diverse group of viruses multiplying primarily in the gastrointestinal tract and/or the upper respiratory tract, initially distributed in two separate genera: Enterovirus and Rhinovirus, respectively. According to the similarities in genome organization and particle structure, rhinovirus species were later reclassified as also belonging to genus Enterovirus. Human EV infections are usually asymptomatic or causing mild clinical manifestations. Nevertheless, some EV infections may derive in severe neural complications, including acute flaccid paralysis (AFP) such as poliomyelitis, whose etiological agent is poliovirus, a member of the Enterovirus C species. The inactivated polio vaccine (IPV) and particularly the oral attenuated polio vaccine (OPV) have contributed to the virtual eradication of the disease. However, sustained global circulation of vaccine-derived poliovirus 2 (cVDPV2), originated from the genetic instability of OPV strain 2 and intertypic recombination between Sabin OPV strains and members of the Enterovirus C species, still causes outbreaks of AFP worldwide. In addition, humanitarian crises, in particular armed conflicts, hamper polio vaccination campaigns and facilitate the occurrence of cases. Additionally, besides poliovirus, other EV may also cause AFP, among them EV A71 or EV D68, and it is highly advisable to implement wastewater surveillance to elucidate the occurrence of not only polioviruses, but also of other EV susceptible to derive in serious neural complications, since the screening of viral RNA in cerebrospinal fluid samples in patients suffering from AFP is not a reliable diagnostic tool.