The book is a linked series of essays. For each essay, I picked a single virus, but I chose ones that allowed me to explore a big idea in the world of virology. In the Audubon excerpt, for example, the virus is West Nile. As viruses go, West Nile is not all that dangerous. But its story is fascinating. West Nile’s tale is the classic American immigrant saga, from its arrival in New York City to its eventual spread across the country. Check it out.