“Bubonic Plague was also carried by rats on trade ships from China to Europe. Just a history note.”
Source of your history note?
There are lots of sources...
https://www.thoughtco.com/black-death-in-asia-bubonic-plague-195144
There are still occasional cases in China, too, including one from Nov 2019
Some people think the Black Death hastened the demise of the Mongolian dynasty in China.
In the fall of 1347 12 ships docked at Sicilian port. Messina.
On board most of those ships, many if not most of the sailors were DEAD.
Those ships came from the Black Sea where they had taken trade in from Asia-China, Mongolia, etc. Why would they have sailed to the Black sea to get those trade goods? Because of the silk trade and spice trade. Silk was the big one.
The Plague spread from there to that Sicilian port and then into Florence and beyond.
Genetic studies of modern and ancient Yersinia pestis DNA suggest that the origin of the Justinian plague was in Central Asia. The most basal or root level existing strains of the Yersinia pestis as a whole species are found in Qinghai, China.
Morelli, Giovanna; et al. (October 31, 2010). “Yersinia pestis genome sequencing identifies patterns of global phylogenetic diversity”. Nature Genetics. 42 (12): 1140–1143. doi:10.1038/ng.705. PMC 2999892. PMID 21037571.
“basal” is the key word here.