Viruses have a simple structure: they are often no more than a set of genes wrapped inside a coat—a “piece of bad news wrapped in a protein coat,” as Peter Medawar, the immunolo-gist, had described them. When a virus enters a cell, it sheds its coat, and begins to use the cell as a factory to copy its genes, and manufacture new coats, resulting in millions of new viruses budding out of the cell. Viruses have thus distilled their life cycle to its bare essentials. They live to infect and reproduce; they infect and reproduce to live.
