Ann Arbor. The world learned today that its hopes for finding an effective weapon against paralytic polio had been realized.
—The New York Times, April 12, 1955
Enteroviruses constitute a major subgroup of small, icosahedral, naked capsid positive-sense RNA viruses belonging to the family Picornaviridae (picornaviruses). Their name is derived from their ability to infect intestinal tract epithelial and lymphoid tissues and shed into the feces, but do not commonly cause gastrointestinal diseases. They are transmitted by the fecal–oral route and readily infect the intestinal tract and further spread to cause paralytic disease, mild aseptic meningitis, exanthems, myocarditis, pericarditis, and nonspecific febrile illness. These viruses include the polioviruses, coxsackieviruses, echoviruses, parechoviruses, and other agents that are simply designated as enteroviruses. There is another member of the picornavirus family called rhinoviruses that are not enteroviruses, because they are transmitted through respiratory route and cause common colds. Enterovirus infections can produce a great diversity of clinical disease. Some cause paralytic disease that may persist permanently (a typical feature of polioviruses), acute inflammation of the meninges with or without involvement of cerebral or spinal tissues, or sepsis-like illnesses in newborn infants. Inflammatory effects at other sites, such as the lungs, pleura, heart, and skin have been also observed, often without concomitant or preceding central nervous system (CNS) involvement. Occasionally, infections may result in chronic, active disease processes. For poliovirus, two types of vaccines, inactivated polio vaccine (IPV) and live attenuated oral polio vaccine (OPV), have been in use in preventing polio worldwide. Moreover, IPV is recommended for use in the United States.
ENTEROVIRUSES: GROUP CHARACTERISTICS
MORPHOLOGY AND BIOLOGIC FEATURES
As a group, the enteroviruses are picornaviruses that are extremely small (22-30 nm in diameter), naked capsid virions with icosahedral symmetry. Enterovirus possess single-stranded, positive-sense RNA with a covalently bound small virus-encoded protein (VPg) and a capsid formed from 60 copies of four nonglycosylated proteins (VP1, VP2, VP3, and VP4). The basic building block of the capsid is the protomer containing one copy each of VP1, VP2, VP3, and VP4. Five protomers (pentamers) are placed at each of the 12 vertices of the icosahedron to form a capsomere of 60 protomers. The shell is composed of VP1, VP2, and VP3, whereas VP4 is attached on the inner surface. On the surface of the virus, there is a deep depression or canyon around each pentameric vertex. The receptor binding site is located at the floor of the canyon. The virion structure of a picornavirus member is shown in Chapter 13 (Figure 13–1). Replication and assembly occurs exclusively in the cellular cytoplasm; one infectious cycle can occur within 6 to 7 hours. This results in cessation of host cell protein synthesis and cell lysis with release of new infectious progeny. The replication cycle is shown in Figure 12–1. Picornaviruses enter the host cell via ...