Picornavirales

Fmicb-09-03235-g008

Picornavirales is an order of viruses in the realm of Riboviria. This order encompasses a variety of viruses that share a similar genetic organization and replication strategy but can differ significantly in their host range, pathogenicity, and clinical manifestations. The name "Picornavirales" is derived from the most well-known family within the order, the Picornaviridae, which includes notable pathogens such as Poliovirus, Coxsackievirus, and Hepatitis A virus.

Classification

The order Picornavirales is classified within the realm Riboviria, which includes all viruses that have RNA as their genetic material and replicate using an RNA-dependent RNA polymerase. Within Picornavirales, there are several families, including but not limited to:

• Picornaviridae: This family contains many of the well-studied viruses within the order, affecting humans, mammals, and birds.
• Secoviridae: Primarily plant pathogens, these viruses have a bipartite RNA genome.
• Dicistroviridae: Infecting a wide range of invertebrates, particularly arthropods, these viruses have a monopartite RNA genome.

Genome and Structure

Viruses in the Picornavirales order typically have a single-stranded, positive-sense RNA genome. The genome is relatively small, ranging from about 7,000 to 8,500 nucleotides in length. The viral particles are non-enveloped and possess an icosahedral capsid structure. The genome encodes a single polyprotein that is post-translationally processed by viral proteases into structural and non-structural proteins necessary for the virus's replication cycle.

Replication Cycle

The replication cycle of Picornavirales viruses begins with the virus attaching to a specific receptor on the host cell surface, followed by entry into the cell. The RNA genome is then released into the cytoplasm, where it serves as a template for both translation and replication. The viral RNA is directly translated into a polyprotein, which is subsequently cleaved into functional viral proteins. Replication of the viral RNA is carried out by a virus-encoded RNA-dependent RNA polymerase. Newly synthesized viral genomes are packaged into capsids, and progeny viruses are released from the cell, typically by cell lysis.

Pathogenicity and Clinical Significance

Members of the Picornavirales order are responsible for a wide range of diseases in humans, animals, and plants. In humans, diseases can range from mild respiratory or gastrointestinal infections to more severe conditions such as poliomyelitis, hepatitis A, and myocarditis. The wide host range and diverse clinical outcomes associated with Picornavirales infections make them of significant interest in both human and veterinary medicine, as well as agriculture.

Prevention and Treatment

Prevention of Picornavirales infections primarily involves vaccination, where available, and adherence to good hygiene practices to reduce transmission. For example, the polio vaccine has been highly effective in controlling poliomyelitis. Treatment options for Picornavirales infections are limited, as there are few antiviral drugs available. Management of symptoms and supportive care are the mainstays of treatment for many of these infections.