Polioviruses (Picornaviridae)

Poliomyelitis is an old disease in humans but it only became a major health problem in the beginning of the twentieth century. It is caused by a poliovirus, a member of the genus Enterovirus of the family Picornaviridae which normally produces an asymptomatic infection in the gut in humans. Killed and live vaccines were developed in the mid-twentieth century, and the live-attenuated oral polio vaccine (OPV) have been employed in massive campaigns as part of the World Health Organization program on the eradication of poliomyelitis with only two countries in the world from which poliomyelitis has never been eradicated. Reappearance of poliovirus infection may be a problem. The molecular basis of the attenuation of the OPV strains is well understood and the strains can revert to cause disease in recipients, or to circulate in the community or be excreted for prolonged periods by patients deficient in humoral immunity. Circulating vaccine derived strains are a major current challenge to eradication.