Infected animals (rats) and people were the main vectors of Bubonic Plague in the middle ages. There was an active trading system even then with ships and cargo going from different parts of the world to multiple destinations. As there was no restrictions on peoples movement (barring access to transport) and the geographical places (for example the Americas) were relatively newly discovered the disease could spread around the world as the people moved. I don't think anyone knows for sure where the plague originated but it was probably from outside Europe and when it arived back to Western Europe due to the people having low resistance levels to the illness (much like the native Americans in the US) there was a serious loss of life.
The bubonic plague started in Asia and spread to Europe.
the bubonic plague, spread by rats bitten bye infected fleas
the world was dirty
Bubonic Plague was spread by being bitten by fleas that had bitten infected rats.
It was spread by fleas. Apex
rats infestation or spread of bubonic plague from rats.
There was the spread of a plague but the exact nature of the plague is unknown. It is widely believed to be a strain of Bubonic Plague.
traders
The Bubonic Plague.
One human activity that contributed to the spread of the bubonic plague was the movement of infected rats on ships, which carried the disease from one place to another.
The bubonic plague was spread mainly by fleas traveling on the backs of rats in cities and through trade on continental Europe while the influenza spread directly from person to person in crowded public subways and gatherings.
bubonic plague carried by rats and spread by fleas