The Bubonic Plague which is also known as the black death mostly targeted the lungs of mammals. The bubonic plague started from the bacteria Yersinia Pestis. This bacteria gave the victims pneumonia.
The bubonic plague spread due to rats and fleas. The rats and fleas spread it because of the bacteria. The bacteria Yersinia Pestis gets passed with bites from fleas and from rats through the food people eat.
The lower class and middle class were more likely to get infected. This was because they had more rats and fleas living in their houses then the rich. The rich were protected and well fed while the peasants were not.
There were no cures known in the middle ages which would actually help against the bubonic plague. They used methods which consisted of gold, rose water, and theriac. The most common method was for plague doctors to come in and perform bloodletting. Bloodletting was the process to try and get the plague out of the patients blood.
The first to use this method were the Mongols into the Black Sea port of Caffa. When planes became popular Japan took fleas and rained them down upon enemies.
Send in the planes!
Fire the catapult!
There were multiple ways people could use the bubonic plague as a weapon. They used catapults to send the plague infested-bodies over castle walls. They also used fleas and rats and sent them into the enemy's territory.