Nomenclature and Classification of Virus: Definition, History, Structure, Classification

What Are Viruses?

Viruses can be defined as tiny infectious microorganisms that can replicate themselves only in the living cells of a host organism. This is important for the analysis of their biological characteristics, ways of dissemination, and consequences for a human’s condition and the environment. There exists virus classification which divides viruses according to the genetic material and the morphology of the virus particle, the method of replication, and the range of hosts that can be affected. This gives clues regarding the virus evolution and the manner of infection.

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Viruses are named depending on the species of the host, the form of the disease that is caused, the geographical origin of the virus or the molecular nature of the virus which enhances intergenerational understanding between scientists and health practitioners. Such a systematic approach not only assists scientific knowledge of diseases and diagnosis but also helps in policy formulation on the control and prevention of viral diseases in different parts of the globe.

History Of Virus Classification

The history of virus classification has been characterised by certain landmarks and outstanding scientists who intervened in the study of these mysterious objects. The first systematic efforts in the 18th century with the classification done by Carl Linnaeus laid the basis of the taxonomical approach of categorising organisms where viruses also fell under this channel of thinking. The critical advancements were made throughout the 20th century, as electron microscopy helped to define the ultrastructure of viruses, as well as virus taxonomy based on the virus morphology.

However, advancements in the 1950s particularly the molecular biology put by researchers such as David Baltimore helped in categorising viruses according to the genetic material and their modes of replication. Maxwell’s complex of Baltimore, the classification of seven groups of viruses based on RNA genome replication strategies, changed the approach to the study of viruses and established a basis for the classification and evolution of viruses.

These landmarks and scientific achievements remain an important foundation for virus classification and make it possible to update the concept of viruses, anticipate the risk of virus-related diseases, and facilitate the search for effective approaches to intervening in viruses at the population level and in medicine.

Principles Of Virus Classification

Taxonomic Hierarchy

They are categorised in a classifying system of Domain Kingdom, Phylum, Class, Order, Family, Genus and Species. This classification helps in categorising viruses in a manner that they share one or more features with other viruses and or evolved from one source.

ICTV (International Committee On Taxonomy Of Viruses)

The ICTV is the major global organisation that supervises the classification and naming of viruses to ensure some form of order and uniformity in the virus classification system in the world. It is rather invaluable in the effort to maintain consistency in the approach towards the categorisation of viruses in the system that informs the systematic consideration and description of viruses by researchers, clinicians, public health officials, and others.

Baltimore Classification

The classification of viruses as placed into a taxonomy system permits their integration into a genetic and replicative framework that is virology. It categorises viruses based on 7 classes (I-VII), which is marked by high resemblance in the process of mRNA synthesis. There is nothing more important than the Baltimore classification when it comes to describing how viruses reproduce themselves and if there can be a method for combating distinct classes of viruses.

Virus Nomenclature

Binomial Nomenclature In Viruses

The classification of viruses according to their type is done in a binomial way with the name of the virus being of the format genus and species (for instance Influenza virus which is categorised under Influenzavirus A).

Examples Of Virus Names (e.g., Human Immunodeficiency Virus - HIV)

Some examples are HIV, HBV, and ZIKV where HV stands for Human, B stands for Birus (indicating the virus is a hepatitis virus) and V at the end of the names denotes virus; ZIKV is an acronym derived from Zika Virus and the disease it causes.

How Virus Names Are Assigned

Some of the viruses Were derived from the geographical areas where it was first found, the species they initially infected, the disease they caused or the person who discovered them. There are international committees comprising experts in virus taxonomy such as the International Committee on Taxonomy of Viruses (ICTV) responsible for guiding how viruses are classified and named to avoid confusion and complex discussions in scientific forums.

Categories Of Viruses

DNA Viruses Vs. RNA Viruses

DNA viruses like T=Herpes simplex virus & Variola virus possess double-stranded DNA genomes along with all types of viruses. Depending on its structure, we have RNA viruses consisting of Single-stranded RNA with Hepatitis C as an example, and single-stranded RNA Influenza virus. Subtypes are defined by their sense (positive or negative) and if their RNA is segmented They are therefore categorised based on the above characteristics based on the sense that they possess either positive or negative sense and the fact that their RNA is in a segmented form.

Single-Stranded Vs. Double-Stranded Viruses

There are different types of viruses depending on how many strands of nucleic acids they contain which can be; single-stranded (ss) or double-stranded (ds) nutshell. Some examples of viruses with positive sense RNA include the Hepatitis C virus which belongs to ssRNA while Rotaviruses belong to dsRNA.

Positive-Sense Vs. Negative-Sense RNA Viruses

The RNA viruses are further classified into positive-sense RNA viruses (for example Poliovirus) and negative-sense RNA viruses (for example Measles virus) depending on whether or not the RNA can be transcribed directly into mRNA for the formation of proteins independently or need an RNA polymerase for this function.

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