Picornaviridae

Family of small RNA viruses, with positive-stranded RNA genome. This family of viruses includes the entero-, rhino-, FMD- and coxsackieviruses. The name is composed of pico = small (22-27 nm) and RNA. The picornavirus family (Picornaviridae) includes non-enveloped (no lipid capsule) viruses with a single-stranded, linear RNA with a very similar gene sequence. Picorna viruses have a so-called plus-stranded RNA genome (positive-stranded RNA genome), i.e. the viral NA is simultaneously used as mRNA after penetration into the cell.

The following list of human pathogenic picornaviruses includes only a very limited selection of species. The Picornaviridae include:

Enteroviruses

• Human enteroviruses A (23 serotypes including coxsackievirus A)
• Human enteroviruses B (60 serotypes including coxsackievirus B and ECHO viruses)
• Human enteroviruses C (23 serotypes including poliovirus type 1-3)
• Human enteroviruses D (>5 serotypes)

Rhinoviruses

• Human rhinoviruses A (77 serotypes)
• Human rhinoviruses B (25 serotypes)
• Human rhinoviruses C (51 serotypes)

Parechoviruses

• Parechovirus (8 serotypes)

Hepatoviruses

• Hepatitis A virus (1 serotype)

Picornaviruses are found in mammals and birds. Currently, there are 80 genera in this family, divided into 35 genera. Furthermore, picornaviruses are subdivided into numerous serotypes, which are characterized by a large surface variance and an associated "antigenic" variability. To date, approximately 370 types have been classified.

The virions (virus particles) of the Picornaviridae are roundish and about 22-30 nm in diameter. All Picornaviridae are equipped with a single- or, more rarely, a double-stranded RNA chain. They are surrounded by a protein capsule, called a capsid, which consists of 4 structural proteins, VP1, VP2, VP3 and VP4. These 4 structural proteins together form a capsomer. About 60 capsomers form an icosahedron of about 30 nm. They are not surrounded by a membrane envelope. The capsids consist of four viral proteins: VP1, VP2, VP3 and VP4. Occasionally, a fifth polypeptide is found in irregular amounts; it is called VP0 and represents the precursor of the components VP2 and VP4, which are formed only during virus maturation by proteolytic cleavage. These are responsible for the antigenic properties and thus for their classification into serotypes.

Picornaviruses lack a lipid-containing envelope. They are also referred to as unenveloped. However, the lack of a lipid envelope implies a particular resistance of picornaviruses to organic solvents such as ethers, alcohols as well as to mild detergents (e.g. soaps). Moreover, the species of the genera enterovirus and hepatovirus remain stable over time even at pH values < 3.0. Due to their acid stability, the viruses of these two genera are not inactivated by the acidic environment in the stomach. Therefore, the general route of infection of picorna viruses is predominantly via the digestive tract and from there to other target organs (CNS, lungs). Most picornavirus infections cause characteristic morphological changes in the host cells. Inhibition of cellular DNA, RNA and protein synthesis occurs. Inhibition of cellular protein synthesis occurs in many picornaviruses by proteolytic cleavage of the protein p220, which is a component of the cellular cap-binding complex.

Picornaviruses are found in mammals and birds. Currently, there are 80 genera in this family, divided into 35 genera. Furthermore, picornaviruses are subdivided into numerous serotypes, which are characterized by a large surface variance and an associated "antigenic" variability. To date, approximately 370 types have been classified. For humans, relevant representatives of the Picornaviridae are: hepatitis A viruses, polioviruses, rhinoviruses, coxsackie viruses and, in animals, foot-and-mouth disease viruses, which can also cause symptoms in humans.

Rhinoviruses mainly infect the nasopharynx. They are frequent pathogens of colds in children and adults. Parechoviruses replicate mainly in the gastrointestinal tract; they cause diarrheal disease mainly in young adults, often with respiratory complications. Picornaviruses further cause meningitis, myocarditis, hand-foot-and-mouth disease (Coxsackie A viruses), pericarditis, and hepatitis A (hepatitis A viruses). Transmission occurs via contaminated food and water and droplet infection. Polioviruses, ECHO viruses and coxsackieviruses primarily infect the gastrointestinal tract of humans.

Parechoviruses are very similar to enteroviruses in terms of their importance and the diseases they produce. They predominantly infect newborns and infants.

Hepatoviruses: The genus Hepatovirus includes 9 species (Hepatovirus A-Hepatovirus I). Hepatovirus A is the causative agent of hepatitis epidemica(hepatitis A), which is present worldwide, but its prevalence is high only in countries with poor sanitary conditions.

An association between picorna virus infections and dermatomyositis is discussed.

The following list of human pathogenic picornaviruses includes only a very limited selection of species.

Acid-stable human pathogenic picornaviruses:

• Poliovirus, types 1-3
• Enterovirus 4 types
• Coxsackie A virus 23 types
• Coxsackievirus B virus 6 types
• Echovirus, 31 types

Acid-labile human pathogenic picornaviruses:

• Rhinovirus about 200 types
• Aphthovirus, foot-and-mouth disease virus, animal pathogenic, 7 serotypes

1. Hengstman GJ et al (2002) Clinical and serological characteristics of 125 Dutch myositis patients. Myositis specific autoantibodies aid in the differential diagnosis of the idiopathic inflammatory myopathies. J Neurol 249: 69-75