A virus (from the Latin virus meaning toxin or poison) is an infectious agent too small to be seen directly with a light microscope. They are not made of cells and can only replicate inside the cells of another organism (the viruses' host). Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 of them have been describ...
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A virus (from the Latin virus meaning toxin or poison) is an infectious agent too small to be seen directly with a light microscope. They are not made of cells and can only replicate inside the cells of another organism (the viruses' host). Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 of them have been described in detail, although there are millions of different types of viruses. 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.
Viruses consist of two or three parts: all viruses have genes made from either DNA or RNA, long molecules that carry genetic information; all have a protein coat that protects these genes; and some have an envelope of fat that surrounds them when they are outside a cell...
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