Classification and Nomenclature of Viruses

Viral taxonomists have developed a system of classification and nomenclature that embraces all viruses. From the operational point of view, viruses are divided into those that affect vertebrate animals, insects, plants, and bacteria. The chapter discusses the viruses of vertebrate animals, although some of these viruses, the arthropod-borne viruses (arboviruses), also replicate in insects or other arthropods. Several hundred species of viruses have been recovered from humans, who are the best-studied vertebrate hosts and new ones are still occasionally discovered. Somewhat fewer have been recovered from each of the common species of farm and companion animals and from the commonly used laboratory animals. To simplify the study of this vast number of infectious agents, these are sorted into groups that share certain common properties. The most important criteria for classification are the physical and chemical characteristics of the virion and the mode of replication of the virus. The chapter explains a formal viral taxonomy, which is based on these criteria.