How did hygienic environment that was created in the French city become the cause of plague?

cbse
cbse-class-10
cbse-class-10-social
nationalist-movement
movement-indo-china

#1

The large sewers in the modern part of the city, a symbol of modernity, were an ideal and protected breeding ground for rats. The sewers also served as a great transport system, allowing the rats to move around the city without any problem. And rats began to enter the well-cared-for homes of the French through the sewage pipes.