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A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. [2] [3] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.
Life-cycle of a typical virus (left to right); following infection of a cell by a single virus, hundreds of offspring are released. When a virus infects a cell, the virus forces it to make thousands more viruses. It does this by making the cell copy the virus's DNA or RNA, making viral proteins, which all assemble to form new virus particles. [37]
Megavirus chilensis is a very large DNA virus discovered in 2010. Until the discovery of Pandoravirus in 2013, it was the largest known virus, with its 440 nm diameter capsid being as large as some small bacteria. The capsid is enclosed in bacterial-like capsular material 75–100 nm thick. Credit: Chantal Abergel (10 October 2011)
A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells. [ 1 ] Examples include the common cold , gastroenteritis , COVID-19 , the flu , and rabies .
Gamma phage, an example of virus particles (visualised by electron microscopy) Virology is the scientific study of biological viruses.It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they ...
Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms.
Virus classification showing major ranks This is a list of genera of biological viruses. See also Comparison of computer viruses. This is an alphabetical list of genera of biological viruses. It includes all genera and subgenera of viruses listed by the International Committee on Taxonomy of Viruses (ICTV) 2022 release. [1]
After tobacco mosaic was recognized as a virus disease, virus infections of many other plants were discovered. [34] The importance of tobacco mosaic virus in the history of viruses cannot be overstated. It was the first virus to be discovered, and the first to be crystallised and its structure shown in detail.