Neurotropic picornaviruses

Introduction The family Picornaviridae includes many important human and animal pathogens, such as poliovirus, hepatitis A virus, foot-and-mouth disease virus, and rhinovirus. All picornaviruses are small, nonenveloped viruses with a single-stranded RNA genome of positive polarity, properties that are reflected in the name of the virus family: pico, a small unit of measurement [10 −12 ], and the nucleic acid of the viral genome, RNA. Poliovirus is the best-studied picornavirus that causes disease of the nervous system, but the family also contains other neurotropic viruses. This chapter will focus on the biology and pathogenesis of picornaviruses that cause neurological disease. Members of the family Picornaviridae are classified into nine genera, four of which contain neurotropic viruses (Table 1.1). Poliovirus, coxsackievirus, echovirus, and other members of the enterovirus genus replicate in the alimentary tract and are resistant to low pH. The cardiovirus genus includes the encephalomyocarditis-like viruses, which cause flaccid paralysis in mice, and the Theiler's murine encephalomyelitis viruses. Different strains of Theiler's viruses cause either a poliomyelitis-like disease in mice or a chronic demyelinating disease similar to multiple sclerosis. Members of the parechovirus genus, previously classified as echoviruses, have been associated with flaccid paralysis and encephalitis. The teschovirus genus consists of porcine teschovirus, which may cause polioencephalitis in pigs. Virus structure Picornavirus virions are 30-nm spherical particles that consist of a protein shell surrounding the naked RNA genome. The virus particles lack a lipid envelope, and consequently their infectivity is insensitive to organic solvents.