Poliovirus 1 is the first serotype of poliovirus, a non enveloped positive sense RNA virus in the Picornaviridae family that causes poliomyelitis. The virus spreads mainly through the fecal‑oral route and infects only humans.
Structure, transmission and epidemiology
Poliovirus 1 is a member of the species Enterovirus C. It has an icosahedral capsid about 30 nm in diameter enclosing a single‑stranded positive‑sense RNA genome. The genome encodes a polyprotein that is cleaved into structural proteins (VP1–VP4) and non‑structural proteins required for replication. Following ingestion, virus replicates in the oropharyngeal and intestinal mucosa and is shed in stool. Viremia can follow, and in a small fraction of infections the virus crosses the blood‑brain barrier to invade motor neurons in the spinal cord. Most infections are asymptomatic or cause minor illness, but neuroinvasive disease leads to flaccid paralysis. Three wild poliovirus serotypes circulated historically. Wild poliovirus type 2 was declared eradicated in 2015 and type 3 in 2019, but wild poliovirus 1 remains endemic in Afghanistan and Pakistan with occasional importations into other regions. Immunisation with inactivated and live attenuated vaccines has dramatically reduced circulation.
Clinical features and public health significance
Infection with poliovirus 1 often produces no symptoms or a mild illness characterised by fever, sore throat and gastrointestinal upset. In a small proportion of cases, transient viremia seeds the meninges and causes aseptic meningitis. Rarely, virus infects anterior horn motor neurons, leading to acute flaccid paralysis that may involve the limbs, respiratory muscles or cranial nerves. Survivors can experience lifelong weakness or post‑polio syndrome decades later. Poliovirus 1 accounted for most cases of paralytic poliomyelitis before vaccination. Global eradication initiatives rely on high vaccination coverage, surveillance of acute flaccid paralysis and environmental sampling to detect silent transmission. Poliovirus 1 remains a key target for eradication. It continues to circulate in a small number of countries, and imported cases can occur where immunisation coverage is incomplete. Maintaining high levels of vaccination and rapid outbreak response are essential to stop transmission. Related Terms: Poliovirus 2, Poliovirus 3, Enterovirus C, Sabin vaccine, Coxsackievirus