How do scientist classify viruses?

For the first 60 years of virus discovery, there was no system for classifying viruses. Consequently viruses were named haphazardly, a practice that continues today. Vertebrate viruses may be named according to the associated diseases (poliovirus, rabies), the type of disease caused (murine leukemia virus), or the sites in the body affected or from which the virus was first isolated (rhinovirus, adenovirus).

Some viruses are named for where they were first isolated (Sendai virus, Coxsackievirus), for the scientists who discovered them (Epstein-Barr virus), or for the way people imagined they were contracted (dengue = ‘evil spirit’; influenza = ‘influence’ of bad air). By the early 1960s, new viruses were being discovered and studied by electron microscopy. As particles of different sizes, shapes, and composition were identified, it became clear that a systematic nomenclature was needed.

Lwoff, Horne, and Tournier suggested a comprehensive scheme for classifying all viruses in 1962. Their proposal used the classical Linnaean hierarchical system of phylum, class, order, family, genus and species. The complete scheme was not adopted, but animal viruses were soon classified by family, genus, and species.

An important part of the scheme proposed by Lwoff and colleagues is that viruses are grouped according to their properties, not the cells they infect. The nucleic acid genome was also recognized as a primary criterion for classification. Other characteristics which were subsequently added include the type of disease caused, and which animals and tissues are infected.