Enteroviruses (EV), so named because most members infect the alimentary tract and are shed in the feces, cause a variety of diseases in humans and lower animals. They constitute 1 of the 6 major subgroups, or genera, of the family Picornaviridae [pico, “small”; rna, “ribonucleic acid”]. The other genera of Picornaviridae are the Rhinoviruses, Cardioviruses, Aphthoviruses, and 2 newly designated genera, Hepatovirus, the prototypic member of which is human hepatitis A virus; and Parechovirus, which contains 2 serotypes that were previously classified as echoviruses types 22 and 23. Three additional genera have been proposed: Erbovirus, Kobuvirus, and Teschovirus.

PHYSICAL AND BIOCHEMICAL PROPERTIES

Enteroviruses, like all members of the Picornavirus family, are small, spherical, nonenveloped viruses approximately 30 nm in diameter. Their genome consists of a linear, single- stranded, unsegmented molecule of RNA (approximately 7500 nucleotides) that has the same polarity as messenger RNA.

Enteroviruses are stable over a wide range of pH (pH 3 to 10) and retain infectivity for days at room temperature, weeks at refrigerator temperature, and indefinitely when frozen at −20°C or lower.

CLASSIFICATION OF ENTEROVIRUSES

Historically, human EV have been subclassified into polioviruses, group A and group B coxsackieviruses, and echoviruses on the basis of antigenic relationships, differences in host range, and types of disease produced (Table 182.1). By 1969, 67 species (serotypes) of human EV had been identified and classified according to these criteria, although reclassification and redundancy have reduced this number from 67 to 61.