Most-recent common ancestor of the bacterium that causes Lyme disease was about 60,000 years ago, well before there were people in the Americas. I don't think the chipmunks were doing gain-of-function experiments. Figure 3 from Walter et al. (2017): doi.org/10.1038/s415...
RFK told Dana Bash that Lyme disease “almost certainly” came from gain of function research. Which is utterly false. www.medpagetoday.com/infectiousdi...