92: Enteroviruses and Parechoviruses

I. DEFINITION

Enteroviruses and parechoviruses are a large group of viral pathogens represented by 2 different 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.

1. Enteroviruses. The genus of enteroviruses traditionally consisted of 5 groups, each with well-known human infant pathogenicity: coxsackie A viruses, coxsackie B virus, echoviruses, numbered enteroviruses, and polio virus. The new classification (based on viral genomic structure) of the enterovirus genus has 4 species: human enteroviruses (HEV) A, B, C, and D. Although they were reclassified, virus serotypes continue to use their original name.

2. Parechoviruses. The genus of human parechoviruses (HPeVs) is made up of 16 described types but 8 sequenced human parechovirus types. Types 1 and 2 were formerly thought to be human enteroviruses 22 and 23, but after the discovery of capsid proteins distinctly different from those of the genus enterovirus, they have been relegated to a single genus. To date, only types 1–3 have been identified in neonatal sepsis-like viral syndromes. HPeV4–6 are associated with gastrointestinal and respiratory symptoms in young infants. Genotypes are continuing to be characterized and identified.

II. INCIDENCE

1. Enteroviruses. 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 fecal–oral route and, to a lesser extent, respiratory droplets. Incubation periods are typically 3–6 days. All subgroups of enteroviruses are linked to nursery and neonatal intensive care unit (NICU) outbreaks of enteroviral diseases.

   Numerous outbreaks of nonpolio neonatal enterovirus have been reported for newborn nurseries, NICUs, and maternity units over the past 3 decades. Overall incidence for newborn and neonatal infants is variable. The Centers for Disease Control and Prevention (CDC) have reported from the National Enterovirus Surveillance System, 2006–2008, that coxsackie B1 virus (CVB1) accounted for 17% of all reported enterovirus isolates. In contrast, from 1970–2005, they had only accounted for 2.3% of cases. During this time there was also an increase in reports of neonatal morbidity and 5 cases of neonatal death in the United States.

2. Parechoviruses. During 2006–2008 surveillance, HPeV type 1 was the most common isolate of that genus, but only accounted for <2% of identified enteroviral suspect specimens. More recently, a report from Edinburgh, Scotland, for enterovirus surveillance from 2006–2010 revealed an incidence of 2.8% for HPeV, but for infants <3 months of age, HPeV type 3 was the predominant isolate (22–25%).