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A virus has either a DNA or an RNA genome and is called a DNA virus or an RNA virus, respectively. The vast majority of viruses have RNA genomes. Plant viruses tend to have single-stranded RNA genomes and bacteriophages tend to have double-stranded DNA genomes.
Virus is a microscopic organism that lives in a cell of another living thing. Although viruses are extremely small and simple, they are a major cause of disease. Some viruses infect human beings with such diseases as measles, influenza, and the common cold.Others infect animals or plants, and still others attack bacteria. Viruses produce disease in an organism by damaging some of its cells.iruses infect all kinds of plants and can cause serious damage to crops. Plant cells have tough walls that a virus cannot penetrate. But insects penetrate the cell walls while feeding on a plant and thus enable viruses to enter. Plant viruses may infect one or two leaves or an entire plant.