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

A virus is a microscopic infectious agent that can only replicate inside the living cells of a host organism. They are composed of genetic material (DNA or RNA) enclosed in a protein coat. Viruses lack cellular structure and metabolism, making them dependent on host cells for reproduction. Virus Nomenclature and Classification involve naming viruses based on their genetic material, structure, host, and mode of replication.

This Story also Contains

1. What Are Viruses?
2. History Of Virus Classification
3. Principles Of Virus Classification
4. Virus Nomenclature
5. Categories Of Viruses
6. Recommended video for "Nomenclature and Classification of Viruses"

Some viruses may have evolved from plasmids, which are pieces of DNA that can move between cells. Other viruses may have evolved from bacteria. This article includes learning about the viruses, the History Of Virus Classification and Virus Nomenclature. Virus is a topic of the chapter Biological Classification in Biology.

What Are Viruses?

Viruses can be defined as tiny infectious microorganisms that can replicate themselves only in the living cells of a host organism. The virus classification 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's evolution and the manner of infection.

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 inter-generational understanding between scientists. 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.

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• MCQ Practice on Virus

• Acellular meaning

• Virus Life Cycle

History Of Virus Classification

The history of virus classification has been characterised by certain landmarks and outstanding scientists who have contributed to the study of these mysterious entities.

1. Early efforts- 18th century

Classification done by Carl Linnaeus laid the basis of the taxonomical approach of categorising organisms where viruses also fell under this channel of thinking.

2. The advancements in the 20th century

The instrument electron microscopy helped to define the ultrastructure of viruses, as well as virus taxonomy based on the virus morphology.

3. Modern Era - 1950s

The researcher David Baltimore helped in categorising viruses according to the genetic material, i.e., DNA or RNA, with their modes of replication inside host cells. It introduced the Baltimore 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

Virus classification helps scientists organize viruses based on their similarities, structure, genetic material, and replication methods. This makes it easier to study viruses, understand how they cause diseases, and find ways to treat or prevent them. They are not classified under any of the five kingdom classification of diversity because they exhibit characteristics of both living and non-living things.

• Taxonomic Hierarchy (Linnaean System)

They are categorised into classification levels as 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 is placed into a taxonomy system that allows their integration into a genetic and replicative framework that is virology. It categorises viruses based on 7 classes (I-VII), which are marked by high similarity 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

Naming viruses properly is very important in virology to avoid confusion and ensure clear communication among scientists, doctors, and public health officials. Virus names are often based on their structure, the diseases they cause, or where they were discovered.

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.

Format: Genus + species

For example, the Influenza virus, which is categorised under Influenzavirus A

How Virus Names Are Assigned

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.

Some virus names are written as acronyms:

• HIV - Human Immunodeficiency Virus

• HBV - Hepatitis B Virus

• ZIKV - Zika Virus

Categories Of Viruses

The viruses are mainly classified based on the type of genetic material (DNA or RNA) inside them and how that functions inside a host cell. These characteristics determine how the virus replicates and causes disease.

DNA Viruses Vs. RNA Viruses

The key difference between DNA and RNA are given as below:

• DNA viruses like Herpes simplex virus & Variola virus possess double-stranded DNA genomes along with all types of viruses.

• RNA viruses consist of Single-stranded RNA, with Hepatitis C as an example, and single-stranded RNA Influenza virus.

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) - Ex Hepatitis C virus

• Double-stranded (ds) - Ex Rotaviruses

Positive-Sense Vs. Negative-Sense RNA Viruses

The RNA viruses are further classified into

• Positive-sense RNA viruses: +ssRNA (for example, Poliovirus) - RNA can directly act as mRNA and make proteins.

• Negative-sense RNA viruses: −ssRNA (for example, Measles virus) - RNA cannot directly make proteins; it needs to be converted to +RNA by RNA polymerase.

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