I. Definition. Enteroviruses are a large group of viral pathogens represented by two genera of the family Picornaviridae. They are all of a single strand of RNA in a capsid of individually distinct polypeptides. The capsid proteins impart antigenicity and facilitate transfer of RNA into the cells of newly infected hosts.
The genus of enteroviruses contains five subgroups of species, each with well-known human infant pathogenicity. They are coxsackieviruses A and B, enteroviruses, echoviruses, and poliovirus. Within each subgroup many numbered subspecies exist, for example, 24 coxsackieviruses A, 6 coxsackieviruses B, 34 echoviruses, 5 enteroviruses, and the polioviruses (types 1, 2, and 3).
The genus of human parechoviruses is made up of two species (types 1 and 2). They were formerly thought to be human enteroviruses 22 and 23, but following the discovery of capsid proteins distinctly different from those of the genus enterovirus, they have been relegated to a single genus.
II. Incidence. Enteroviruses are of worldwide distribution and produce human illness of varying severity, from mild coryza to life-threatening multisystem disease. The diseases have some seasonal variation such as summer-fall in temperate zones but of little variation in the more tropical regions of the world.
Of special interest to neonatologists is the now well-established enteroviral transplacental passage, enteroviruses detected in breast milk, and vertical passage of enteroviruses within first-degree family members without clinical signs of illness. Enteroviral illnesses are transmitted by the oral to fecal route and, to a lesser extent, respiratory droplets. Incubation periods are typically 3–6 days. All subgroups of enteroviruses are linked to nursery and NICU outbreaks of enteroviral diseases.
Numerous outbreaks of nonpolio neonatal enterovirus have been reported for newborn nurseries, NICUs, and maternity units over the past three decades. Overall incidence for newborn and neonatal infants is variable, but one report gave an incidence of all neonatal nonpolio enteroviral diseases in 666 infants cultured sequentially in the summer and fall 1981 as 12.8%. More specifically, the Centers for Disease Control and Prevention (CDC) have reported from the National Enterovirus Surveillance System (NESS), 1983–2003, that neonatal enteroviral illnesses accounted for 11.4% of all reports. Most common neonatal serotypes were echovirus serotype 11 (14%), and coxsackievirus serotypes B 2, 4, 5 (33.2%). Neonatal deaths were reported as 3.3%. More recently, for the year 2007, the CDC reported, through the resources of NESS, 444 cases of neonatal enterovirus infections of which 25% were identified as coxsackievirus B1.
III. Pathophysiology. Human enteroviruses manifest disease in nearly all body systems. Paradoxically, signs of disease can be mild to nearly nonexistent or life threatening within the same serotype. Host susceptibility seems to be the distinguishing factor. For the great majority of children and adults, enterovirus and parechovirus illnesses are mild, but for the neonate, a more susceptible host, enteroviruses and parechovirus can cause serious multiorgan dysfunction and death. Some human enteroviruses are more pathogenic than others. Examples of the more serious infections by nonpolio enterovirus serotypes are echo 11, coxsackie B3, coxsackie A9, enterovirus 71, and ...
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