Virus Definition

A virus is a microscopic infectious agent that can only replicate in 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. They infect a wide range of hosts, including animals, plants, and bacteria, often causing diseases.

This Story also Contains

1. Virus Definition
2. What is a Virus?
3. Viruses Structure
4. Types of Viruses
5. Impact Of Viruses On Health
6. Viruses Preventive Measures
7. Recommended video for Virus Definition

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 Virus definition, structure, and composition of viruses. Virus is a topic of the chapter Biological Classification in Biology.

Virus Definition

In biology, viruses are biological agents having the characteristics of both living and non-living organisms. They comprise a nucleic acid core and a protein coat. They are called pathogens because of their capacity to penetrate cells and degrade the host cell’s machinery for their reproduction. The knowledge about viruses plays an important role in understanding basic processes of life as molecular genetics and interactions between the host and virus.

Furthermore, in medicine, the study of viruses enables approaches in diagnosing, treating, and preventing viral diseases that affect human, animal, and plant life throughout the world. Hence, the knowledge of viruses not only helps advance the concept of biological knowledge but also stands as a key guard in defending the population's overall health.

What is a Virus?

Viruses are non-living parasites that can only reproduce with the help of a host cell, and their structure consists of a nucleic acid core, either DNA or RNA, surrounded by a protein capsid. Viruses are of electron micrograph dimensions of 2 to 10 micrometres, while cells are much bigger and can range from 10 to 100 micrometers in diameter.

They generally contain a nucleic acid, either DNA or RNA, surrounded by a protein shell known as a capsid. Viruses are acellular and therefore unable to perform metabolic activities independently. They are not classified under any of the five kingdom classification of diversity because they exhibit characteristics of both living and non-living things.

Virology is the field of microbiology that deals with the study of viruses in structure, classification, genetics, and mechanisms of infection and replication in host organisms.

Also read:

• MCQ Practice on Virus

• History of Virus

• Nomenclature and Classification of Viruses

Viruses Structure

Viruses are simple infectious agents composed of genetic material enclosed in a protective protein coat, and sometimes a lipid envelope. The structure and composition of viruses are discussed below-

• Genetic Material

Viruses can be of many types, and the genetic material can be in the form of DNA or RNA. DNA viruses contain double-stranded or single-stranded DNA molecules, whereas RNA viruses contain single-stranded RNA. Thus, the differences between these viruses impact the methods of replication and the enzymes necessary for the replication of the genome and transcription.

• Capsid

In addition, the capsid is the hard shell that encloses the viral nucleic acid and shields it from environmental aggression. It is made up of protein particles known as capsomeres, which are arranged in different symmetrical forms. The capsid is involved in viral attachment to host cells, entry, and sheltering of the genetic material during inter-host transfer.

• Envelope

An envelope is often present around some viruses and is made up of a lipid bilayer, which is taken from the host cell membrane. The viruses that are enveloped in their structure obtain the coat in the process of budding off the host cell. Sometimes this envelope can carry viral glycoproteins that help the virus identify and attach itself to the host cell. In actuality, none of the viruses possess an envelope, and the viruses that do not are referred to as the non-enveloped or naked viruses. The type of envelope affects the stability of viruses and the mode of transmission, besides being sensitive to conditions such as pH and temperature.

Types of Viruses

Viruses can also be classified based on the type of host they infect and the transmission methods.

• Animal Viruses infect animals, including humans. An example is the influenza virus, the rabies virus, and the coronavirus responsible for COVID-19.

• Plant Viruses infect plants, leading to diseases that most generally affect crop yield and quality. Examples include the tobacco mosaic virus and the cucumber mosaic virus.

• Bacteriophages, or phages, infect bacteria. Examples would include T4 phages that infect bacteria such as E. coli.

• Retroviruses are RNA viruses that make use of reverse transcriptase, a single-stranded RNA that duplicates into DNA, which then integrates into the genome of the host. One such famous retrovirus is HIV, which causes AIDS.

• Arboviruses are transmitted by arthropod vectors, sometimes infecting both humans and animals. Diseases like dengue fever, Zika virus, and West Nile virus are some of those caused by these viruses.

Impact Of Viruses On Health

Viruses can cause a wide range of illnesses in humans, from mild infections like the common cold to serious diseases like AIDS and COVID-19. The impact of viruses on health is listed below-

• Influenza

Responsible for flu episodes during winter with such signs as fever, cough, and aching muscles that result in pneumonia.

• HIV/AIDS

It reduces the immune system and hence makes individuals prone to infections and cancer. AIDS can therefore be described as the last stage of Human Immunodeficiency Virus infection, commonly referred to as Acquired Immune Deficiency Syndrome.

• COVID-19

It is caused by SARS-CoV-2. Although it causes mild to severe pneumonia and ARDS, it is impacting the world’s health significantly.

• Hepatitis

Various viruses, such as A, B, and C, affect the liver to cause inflammation that leads to phenomena such as jaundice, fatigue, and in the chronic stages cirrhosis and liver c, cancer.

Viruses Preventive Measures

Preventive measures help stop the spread of viruses and control infections. Methods like vaccination and antiviral drugs are important to reduce illness and protect health.

• Vaccination

Vaccines help the body develop immunity to particular viruses: either by preventing the occurrence of an illness or, in case the virus gets inside the body, minimising its impact. The immunisation campaigns have proven vital in the fight against viral ailments like influenza, measles, and polio, among others.

• Antiviral Drugs

These medications can affect the virus replication or proteins and decrease its copy in the body, or lessen the symptoms. They are employed to provide relief in conditions like influenza, HIV/AIDS, hepatitis, and so on to better control the epidemic and to reduce the severity of the illness.

Also Read:

Recommended video for Virus Definition