As a kid growing up in rural Alabama in the 1960s and 1970s....I have to admit....I just never saw a rat. Never. Mice? Sure, but not rats.
In fact, it wasn't until the mid 1980s....that I got to Panama, and really started to see rats (big ones).
So this Baltimore thing on rats that President Trump hyped on....kinda interests me.
Generally, when you get to an area where there's rats....there five key elements at work. First, you have open trash or food to feed a growing rat population. Second, you need homeless folks in significant numbers, which are tied into the open off/trash situation. Third, you need heroin addicts or drugged-up idiots who simply don't care about sanitation. Fourth....you need a city council and sanitation department which has zero interest in controlling the rats. Fifth and final, you need decent weather (unlike harsh Montana winters).
The best way to handle an entire neighborhood of rats? You put out a massive amount of rat-poison, and you dispose of the dead rats as quickly as possible. On top of that, you dispose of the buildings that are unused or taken over by addicts.
Why Baltimore can't take actions? That's a question that only a local guy there can answer.