Abstract
Viruses are infectious agents that multiply by entering live cells and using the biosynthetic machinery and other services of the host cells to produce new virus particles. Because they themselves have no metabolism, motility, or other complex functions associated with cell life, they can be extremely small and their structure can be simple. However from initial cell entry to release of progeny virus, they are entirely dependent on assistance by the host cells. To understand viruses and virus-induced diseases, cell biological understanding is of paramount importance. In this article, some basic properties of animal viruses and virus-host cell interactions are discussed.