Vincent, Alan, and Rich celebrate the 200th episode of TWiV by visiting the National Emerging Infectious Diseases Laboratories at Boston University Medical Center, where they meet with Elke, Paul, and Ron to talk about building and working in a BSL4 facility.

Vincent, Dickson, Alan, Rich and Welkin discuss the nature, origin, and evolution of endogenous retroviruses (ERVs), and the recent finding of endogenous filovirus genomes in mammals.