How did the great mortality spread person to oerson

Through the plague ...

The plague spread mainly because of animals and unsanitary conditions in European towns. This disease, carried by rats was often passed on to other animals which were handled by humans. Since towns were dirty and unsanitary, disease was able to spread very quickly. Streets were unclean, etc. Once a few people were sick, it was easy to spread the disease to more people who came in contact with them. The plague was very contagious!