Let’s talk about virus. Virus is a biological agent that reproduces in the cell of living host. When infected by virus, the cells in living host are forced to copies thousands of original viruses that resides in living host. Virus has causes lot of major diseases such as HIV, H1N1 and the latest outbreak which is covid 19. Nowadays, there is a treatment called virotherapy. It is a treatment using biotechnology to change viruses to a therapeutic agent by reprogramming it to treat diseases. Virus is important to evolution such as transfer genes between bacteria