Chapter 301: Enterovirus and Parechovirus Infections

INTRODUCTION

The enteroviruses constitute a genus within the Picornaviridae family of viruses. As their family name implies, these viral agents are small (ie, “pico”), ribonucleic acid (RNA) genome (ie, “rna”) viruses (ie, “viridae”). Traditionally, the genus Enterovirus was speciated into 5 groups: polioviruses, group A coxsackieviruses, group B coxsackieviruses, echoviruses, and numbered enteroviruses (Table 301-1).

The current taxonomic classification of the enteroviruses (EVs) is based on genomic, molecular, and biologic characteristics of the viral isolates and divides the enteroviruses into 13 species. The original enterovirus serotypes have been assigned to the species EVs A to D (see Table 301-1). Together with recently identified types, EVs encompass > 100 types. Additionally, the rhinoviruses, previous assigned to a genus unto themselves, are now considered a species (rhinovirus A–C) within the genus. Lastly, using the revised classification schema, 2 EV serotypes, 22 and 23, have been reassigned to a new genus designated Parechovirus (PeV). There are 4 species of PeV (A–D), with those designated as PeV A (19 types) being responsible for disease in humans.

PATHOGENESIS AND EPIDEMIOLOGY

Morphologically, the EVs and PeVs are small, icosahedral-shaped virions that lack an envelope. The enteroviral capsid is composed of 60 units each of 4 viral capsid proteins: VP1, VP2, VP3, and VP4. The capsid of the PeVs is comprised of 60 units each of 3 viral capsid proteins: VP0, VP3, and VP4. The EVs and PeVs are acid, ether, and chloroform stable and insensitive to nonionic detergents. They are inactivated by heat (> 56°C), ultraviolet light, chlorination, and formaldehyde. These characteristics confer environmental stability to the viruses, permitting them to survive for days to weeks in water and sewage.

The RNA genome of the EVs and PeVs is approximately 7.4 kb in length and serves as a template for viral protein translation and RNA replication (Fig. 301-1). It is organized into a long (~740 nucleotides) 5-nontranslated region (5′NTR), which precedes the single open reading frame. The open ...