Viruses can infect various living organisms, including plants, animals, and even bacteria. Viruses are microscopic that a microscope is needed to visualize them.
When a virus infects a living organism, it injects an infectious agent that can only replicate within the host organism. This infectious agent is called a viral genome which consists of DNA or RNA in RNA viruses. Genomes of viruses , just like any other genomes, contain genes that enable virus to multiply.