Sometimes it can take a considerable time to eradicate vermin, it can be very persistent, and requires constant monitoring, and at times harsh treatment.
Fifty odd years ago there was a mass attempt in the UK to rid our streets of this menace.
Fast forward to New York today, and the stench of vermin remains, and is still getting harsh treatment. It is the only way to keep the vermin off our street. You have to keep o0n top of it, or it will spread.