Picornavirales
Introduction
The order Picornavirales is a group of viruses that belong to the realm of Riboviria, which includes some of the most well-known and widely studied viruses. This order is characterized by its non-enveloped, icosahedral virions and single-stranded RNA genomes. The Picornavirales order includes several families of viruses that infect a wide range of hosts, including humans, animals, and plants.
Taxonomy
The order Picornavirales is divided into several families. These include the Picornaviridae, Dicistroviridae, Ifaviridae, Marnaviridae, Polycipiviridae, Secoviridae, and Solemoviridae. Each of these families contains a number of genera, which in turn contain numerous species of viruses.
Structure and Genome
Viruses in the Picornavirales order are non-enveloped and possess an icosahedral capsid. The capsid is made up of 60 copies each of four different proteins. Inside the capsid is the viral genome, which is a single-stranded RNA molecule. The genome is positive-sense, meaning it can be directly translated into proteins by the host cell's machinery.
Replication Cycle
The replication cycle of Picornavirales viruses begins with the attachment of the virus to the host cell. The virus then enters the cell and uncoats, releasing its RNA genome into the cytoplasm. The viral RNA is then translated into a polyprotein by the host cell's ribosomes. This polyprotein is subsequently cleaved into individual viral proteins.
The viral RNA is then replicated, using a viral RNA-dependent RNA polymerase. The new viral genomes are packaged into capsids to form new virions. These virions are then released from the cell to infect other cells.
Pathogenesis and Clinical Significance
Viruses in the Picornavirales order are responsible for a wide range of diseases in humans and animals. For example, the Picornaviridae family includes the polioviruses, which cause polio, and the rhinoviruses, which are a common cause of the common cold. Other Picornavirales viruses can cause diseases in plants, including several economically important crop diseases.
Research and Future Directions
Research into Picornavirales viruses continues to be a major focus of virology. This research has led to significant advances in our understanding of viral replication, pathogenesis, and immunity. In addition, it has led to the development of effective vaccines and antiviral drugs. Future research will likely continue to focus on these areas, as well as on the development of new diagnostic and therapeutic strategies.