Viruses, like bacteria are found almost everywhere; in the soil, in the air, on surfaces or in animals and plants. They are looking for a host organism to infect so that they can use the machinery in the cell to multiply and create more viruses. Viruses are choosy about what they infect; plant viruses will only plants, some viruses only infect bacteria whilst others infect animals. Often a virus will be able to infect different species e.g. different animals, but will only cause disease in a few.See the American Society for Microbiology website for more information.