What Carried The Black Death To Other Hosts?

The Black Death was a very infectious disease in the 1300's. It was spread in many ways resulting in a mass spread across Europe. One of the most common carriers of The Black Death were flees. Flees attached themselves to rats which entered cities through sewer systems. Cities and towns were not very sanitized so they're was more rats. Flees would then attach themselves to humans and bite them, causing swelling lymph nodes that create buboes. Once a human was infected with The Black Death, they're was a small chance that other people could be infected by coming into contact with infected skin or coughing. The Black Death is a pathogen, which means