Actually, what I found most interesting was tracing back the origin of the virus in the human population even further back. Last time I read about this, it had been traced as far back as 1959 based on stored blood samples. Also of note is that improvements in transportation infrastructure at the beginning of the 1900's allowed spread of the virus. The same arguments that have been made today with the spread of bird flu or SARS via air transport and the further spread of HIV in Africa back in the 80's and 90's along long-distance trucking routes.