Each Friday this month, I’m having a conversation about viruses to mark the publication of my new book A Planet of Viruses. Last week, I talked to virologist Ian Lipkin about the search for new viruses and their potential to alter our behavior. Today, I’m delighted to talk with Richard Preston, the author of the Hot Zone and other books on viruses. He and I discuss the fate of smallpox. The worst viral killer in the history of civilization is now wiped off the face of the Earth, except for some laboratory stocks. Preston and I take on the question of whether we should now annihilate it. Check it out.