Answer :
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.
A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all from animals and plants to microorganisms, including bacteria and archaea.