polioviruses

Polioviruses are enteroviruses that cause poliomyelitis in humans. They belong to the family Picornaviridae, genus Enterovirus. Polioviruses are small, non-enveloped, icosahedral viruses with positive-sense single-stranded RNA genomes of about 7.5 kilobases. There are three serotypes, PV1, PV2, and PV3, which share antigenic properties but differ in neurovirulence.

Transmission occurs primarily by the fecal-oral route. After ingestion, the virus replicates in the oropharynx and intestinal tract and may spread to the lymphatic system and bloodstream. In some cases it invades the central nervous system, destroying motor neurons in the anterior horn of the spinal cord and brainstem, causing poliomyelitis.

Most infections are asymptomatic or cause mild illness. A minority develop nonparalytic meningitis or paralytic poliomyelitis, which presents as acute flaccid paralysis that is often asymmetric and may impair respiration if bulbar motor neurons are involved.

Diagnosis relies on isolation of the virus or detection of viral RNA in stool, throat swabs, or cerebrospinal fluid. There is no widely available antiviral treatment; care is supportive.

Prevention centers on vaccination. The inactivated poliovirus vaccine (IPV) induces humoral immunity and is widely used; the oral poliovirus vaccine (OPV), containing attenuated strains, has aided eradication but can rarely cause vaccine-associated paralytic poliomyelitis and circulating vaccine-derived poliovirus.

Global polio eradication efforts led by the World Health Organization have reduced cases dramatically. Endemic transmission remains limited to a small number of regions where vaccination coverage is incomplete, but surveillance and immunization campaigns continue to aim for interruption of all transmission.