Virus Classification System

A virus classification means establishing a taxonomic system in which viruses are placed and named. There are different classification systems for viruses mostly due to the pseudo-living nature of viruses which does not allow a biological classification like there are for cellular organisms. Classifying viruses can be made depending on the phenotypic characteristics (morphology, nucleic acid type, mode of replication or hosts or the disease they are responsible for).

One of the classification systems is the one defined by the International Committee on Taxonomy of Viruses (ICTV) which began classifying the viruses in the 1990s. The system is based on the same taxon structure as the classification system for cellular organisms. The levels of this type of classification are the following: the Order (followed by the taxon suffix in italics; -virales), then the Family (-viridae), Subfamily (-virinae), Genus (-virus ) and Species. There are basically six orders that were established by the ICTV and these are the Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, Picornavirales, and Tymovirales. According to the Baltimore viruses classification there are seven groups of viruses. This system was first established in 1971 and the viruses are placed on one of the seven groups depending on the combination of their nucleic acid, if they are single-stranded or double-stranded, sense and method of replication. The groups are labeled with roman numbers as following I: dsDNA viruses, II: ssDNA viruses, III: dsRNA viruses, IV: (+)ssRNA viruses, V: (-)ssRNA viruses, VI: ssRNA-RT viruses, VII: dsDNA-RT viruses. Classification of viruses is also made by the Holmes classification system, defined in 1948. This system classifies the viruses in three groups under a single order which is Virales. It is system of binominal nomenclature and the groups that the viruses can be placed into are group I (Phaginae; viruses that attack bacteria), group II (Phytophaginae; viruses that attack plants) and group III (Zoophaginae; viruses that attack animals). Other available system is the LHT System which uses the chemical and physical characteristics as a criteria for classifying the viruses.

The influenza virus is the virus causing infectious diseases in birds, mammals and humans. There are three types of influenza viruses (Influenza A, Influenza B and Influenza C) and they are part of the group V viruses in the Baltimore classification along with the deadly Ebola virus, Marburg virus and rabies. The group V viruses have genomes with a negative-sense single-stranded RNA. Influenza virus is part of the Orthomyxoviridae family along with the Isavirus (the virus causing Infectious salmon anemia) and Thogotovirus. The influenza viruses are the ones responsible for the seasonal flu and seasonal pandemics. The symptoms experienced by a person infected with influenza virus are usually fever, chills, sore throat, muscle pain, weakness and general discomfort. In severe cases can lead to pneumonia which can be life threatening.

 viruses classification

The virus classification systems is actually a taxonomic system useful for scientists to detect easier the genome of a virus that has already been studied, the chemical and physical characteristics of it or the disease that it can cause.