Editor’s Note: Some viruses cause the common cold, and some are crucial to human survival. As world health leaders try to determine how to respond to the new coronavirus, virus expert Marilyn J. Roossinck answers a few questions.
1. What Is a Virus?
Defining a virus has been a challenge, because every time we come up with a good definition, someone discovers a virus that breaks the rules. Viruses are entities that infect cellular life. They are very diverse. The simplest just have a couple of genes made of RNA or DNA wrapped up in a protein coat. Others have hundreds of genes, more than some bacteria.All viruses are ultimately parasites. They require a host for replication. They cannot generate their own energy like cells can.