It is a general concept that iron cuts iron. Keeping this view under consideration many harmful insects have been killed by using virus. The mouth disease of rabbit is cured by using Myxonea virus. It kills pests.
The word virus is derived from the Latin language, which means morbid poison. Various serious diseases such as Influenza, Polio, and Smallpox are caused by virus. Viruses are obligate parasites. They are studied under Electron microscope. Among the plant viruses, Tobacco Mosaic Virus (TMV) has been studied in great detail.
The difference between Bacteria and Virus are : Bacteria are covered by a cell wall made upon of polysaccharides, protein and lipids whereas Viruses are covered by a sheath of protein called capsid.
Viruses are obligate parasites. They have living as well as non-living properties. They are like inert chemicals outside the living host. But they multiply actively inside the living host cells and produce their own types.