So the plague entered Europe around the 1340's, so I was right with the time, but I do know that people in those times believed some strange things about the Gypsies. You are right about the reason for this, I have already heard of this reason before while I did research on the subject.
You are wrong about part of it though...The early Romani were actualy quite clean people, these are just some of their customs that they used to practice and some still practice today: They wash man and female clothing seperatly, they don't eat food that has fallen on the floor, they will never have pets inside their living quarters.
True, many Romani living in poverty today live in dirty conditions, but during the middle ages things were different...For one thing, if a group of Romani were cooking food in a cooking pot, then it was made a law that people could come up and tip all the food out to see if there were human parts being cooked, because people also believed that they were canibals, and because of this the Roma often had to remake the entire meal or go without because they refused to eat off the ground.
Also, there are deffenitly Tribes of Roma and Sinti that live in really clean places today, homes or caravans or wagons, they can live really spotlessly clean!
The Jews also had a hard time, people in those times were quite distrustful of them, they spoke a different language, believed in a different religion...it's the same with any race that has been different to the majority. People tend to be afraid of the unknown, which can end in a lot of bad persacution!
It is nice to talk to someone who knows a thing or two about history!