A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. When infected, a host cell is forced to rapidly produce thousands of identical copies of the original virus. Most virus species have virions too small to be seen with an optical microscope. The study of viruses is known as virology, a subspeciality of microbiology.
About Virus in brief
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. When infected, a host cell is forced to rapidly produce thousands of identical copies of the original virus. Most virus species have virions too small to be seen with an optical microscope, as they are one-hundredth the size of most bacteria. The study of viruses is known as virology, a subspeciality of microbiology. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. Some viruses, including those that cause AIDS, HPV infection, and viral hepatitis, evade these immune responses and result in chronic infections. The word is from the Latin neuter vīrus referring to poison and other noxious liquids, first attested in English in 1398 in John Trevisa’s translation of Bartholomeus Anglicus’s De Proprietatibus Rerum. In 1884 French microbiologist Charles Chamberland invented the filter with small enough pores to remove all bacteria from a solution passed through it. Louis Pasteur was unable to find a pathogen for rabies and speculated about a causative agent for a rabies. The term virion is also used to refer to a single viral particle that is released from the same type of cell and is capable of infecting other cells of same type.
The English word is a mass noun, which has no classically attested plural, which dates to 1948. The Latin word is virulent, whereas the English word for viruses is virus, whereas the Latin word for viral particles is virulentus, which dates to c. 1400. A meaning of \”agent that causes infectious disease\” was first recorded in 1892, long before the discovery of viruses by Dmitri Ivanovsky, who described a non-bacterial pathogen infecting tobacco plants. Since then, there have been more than 6,000 virus species described in detail of the millions of types of viruses in the environment. Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity. The infectious dose of norovirus required to produce infection in humans is less than 100 particles. HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood. Norovirus and rotavirus, common causes of viral gastroenteritis, are transmitted by the faecal–oral route, passed by hand-to-mouth contact or in food or water. Influenza viruses are spread by coughing and sneezing. Virus infections in animals provoke an immune response that usually eliminates the infecting virus. Immune responses can also be produced by vaccines, which confer an artificially acquired immunity to the specific viral infection. Several antiviral drugs have been developed.