The family Picornaviridae is one of the largest of the viral families, and contains some of the smallest (pico) RNA viruses known to infect man.
The family is divided into five genera: enteroviruses, rhinoviruses (cause of the common cold), cardioviruses, apthoviruses and hepatoviruses (cause of hepatitis A).
The enterovirus genus is so-called because these viruses generally replicate in the intestine. The most important enterovirus pathogens include poliovirus and Coxsackie A and B viruses.
Virions are icosahedral and about 30nm in diameter. Each capsid is composed of 60 copies of 4 structural proteins - VP1, VP2, and VP3 are exposed on the virion surface, while VP4 lies buried in close association with the RNA core.
Immunogenic sites are located on the exposed external parts of the capsid. The electron micrograph illustrates an immune complex of enterovirus particles linked by antibody molecules.