It is amazing how fast disease spread in the early years of civilization with primitive shipping and overland caravans.
I saw a video a while back about the spread of the Spanish Flu from Europe back to the US and Canada via returning WW I soldiers. They came home on ships and immediately boarded trains to get to their homes throughout the US and Canada. The spread was incredibly fast. The first transcontinental railroad in North America was completed only 50 years earlier and very quickly became a vector for fast disease transmission.
It was called “The Spanish Flu”, because Spain was the only country at the time that didn’t censor reports on the Flu.