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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.
The coevolution, or "virus-first" hypothesis, conflicts with the definition of viruses, because viruses depend on host cells. [ 20 ] [ 21 ] Also, viruses are recognised as ancient, and to have origins that pre-date the divergence of life into the three domains . [ 22 ]
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 ...
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 .
Of those, about 320,000 types of viruses infect mammals but there are just 219 known to infect humans, according to the U.S. National Library of Medicine. 52 Things You Need to Know About Viruses ...
The virus can spread to different organs throughout the chicken. [131] The virus is transmitted by aerosol and food contaminated by feces. Different vaccines against IBV exist and have helped to limit the spread of the virus and its variants. [127] Infectious bronchitis virus is one of a number of strains of the species Avian coronavirus. [133]
This is an accepted version of this page This is the latest accepted revision, reviewed on 27 February 2025. Computer program that modifies other programs to replicate itself and spread Hex dump of the Brain virus, generally regarded as the first computer virus for the IBM Personal Computer (IBM PC) and compatibles A computer virus is a type of malware that, when executed, replicates itself by ...
Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms. Viruses are classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause.