It is my undertanding the the Black Death came into Europe from Middle East Ports by ship rats debarking in places like Italy. The rats might have gotten to the ports via the trade routes, but the final step was by sea. An interesting book is Rats, Lice and History by Zinzer (sp?).
I read it was transported via the fleas that accompanied the caravans from China to Europe. One, both or neither might be true. We’ll probably never know at this point. History is always somewhat suspect.