viruses can replicate in a way that is destructive to the host cell and this accounts for the fact that some viruses are agents of disease. we cover a number of human diseases caused by viruses in Chapter 33 and 34. However, viruses may also inhabit a cell and replicate in step with the cell without destroying it. Like plasmids and (transposeble element) , viruses may confer important new properties on their host cells. These properties will be inherited when the host cell divides if each new cell also inherits the viral genome. these changes are not always harmful and may even be beneficial.