polioviruses

Being non-enveloped, polioviruses resist gastric acid, bile, and detergents, which suits faecal-oral transmission and environmental persistence, and their positive-sense genome acts directly as mRNA on entering the cytoplasm, translated as a single polyprotein cleaved by viral proteases. They bind CD155 (the poliovirus receptor) on host cells. Three serotypes exist, and immunity is type-specific, which is why vaccines must be trivalent or, as eradication has proceeded and types 2 and 3 have been certified eradicated, adjusted accordingly. Most infections are subclinical; the pathogenic sequence proceeds from oropharyngeal and intestinal replication through viraemia to the central nervous system in a small minority. The primary sites of replication in gut lymphoid tissue explain prolonged faecal shedding and why environmental surveillance of sewage is used for eradication monitoring. Related enteroviruses in the same genus include coxsackieviruses, echoviruses, and enterovirus 71, all sharing summer-autumn seasonality and a capacity for aseptic meningitis.