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what is virus
A virus is a small infectious agent that can only replicate inside the cells of another organism. The word is from the Latin ''virus'' referring to poison and other noxious substances, first used in English in 1392. ''Virulent'', from Latin ''virulentus'' (poisonous), dates to 1400. A meaning of "agent that causes infectious disease" is first recorded in 1728, The term ''virion'' is also used to refer to a single infective viral particle. The plural is "viruses".

Viruses are too small to be seen directly with a light microscope. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. although there are millions of different types. Viruses are found in almost every ecosystem on Earth and these minute structures are the most abundant type of biological entity. The study of viruses is known as virology, a sub-specialty of microbiology.


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