Biological Characteristics and Scientific Classification of Viruses
Viruses are pervasive biological entities associated with organisms in every domain of cellular life. They infect animals, plants, fungi, bacteria, archaea, and many unicellular eukaryotes, and viral genetic material is also found integrated into host genomes. The original essay correctly emphasized that viruses differ fundamentally from cellular microorganisms: they do not possess an independent metabolism, they do not grow by cell division, and they require a host cell to produce

