I actually was under the impression that Lyme disease was a new world disease introduced to Europe after contact, but it seems it was endemic to both continents for thousands of years prior, not clear where it originated as the sources contradict each other. Seems like Europe is more likely.

>In all, 33 different combinations of the housekeeping genes were found. The study's findings appear to show that Borrelia burgdorferi originated in Europe but that the species has been present in North America for a long time. The researchers suggest its re-emergence there in the 1970s occurred after the geographic territory of the tick that carries the bacteria expanded, for example through the restoration of woodland.

https://www.sciencedaily.com/releases/2008/06/080629142805.h...

>A team of researchers led by the Yale School of Public Health has found that the Lyme disease bacterium is ancient in North America, circulating silently in forests for at least 60,000 years—long before the disease was first described in Lyme, Connecticut, in 1976 and long before the arrival of humans.

https://medicine.yale.edu/news-article/ancient-history-of-ly...