Reply to Tournier, "Pandemic Legion History More Complex than Previously Thought".

We thank Dr. Tournier for his comments, which highlight the importance of using modern tools and modern knowledge to look backwards in time to try to understand new disease emergences. We want to emphasize for readers that we neither believe nor meant to imply that phylogenetic dating of viruses and bacteria strictly reflects what is referred to as “emergence.” It is accepted, for example, that the first human infections with HIV probably occurred at some time between the late 1800s and early 1900s, and yet we date the emergence of HIV/AIDS …