"Norminn" wrote
If neighbors have rats, too,then it is a city issue. Call your city
building department or code enforcement.

Was there recent demolition of a nearby structure that drove them out of
"old" habitat? Cold or warm climate?

Any signs on outside of building that the rat chewed it's way in? Gaps
around foundation or roof?

Rats carry some serious dirt - I would get the situation taken care of
pronto.

This is a not-so-typical situation. It's an old commercial/residential
building, in a mixed-use neighborhood, about 78 years old, in a rural area,
next to a river. There are places all over the buildings where rodents
could get in, and aside from the occasional mouse, rodents have never been a
real problem. Set a trap or two, never see another one for 6 months or a
year. Rats, on the other hand, seem to be much tougher to get rid of, and
this is my first experience with them.

Here's the story. Several months ago, some guy about a block away opened a
fish market. It failed within weeks, and he dumped a bunch of fish stuff on
the banks of the river nearby (he's currently in trouble and facing
prosecution, so I'm told). The dumping attracted flies and well, you get
the idea. It was about this time that the rats showed up, and from talking
to neighbors this was the first time for them, also. They seem to have
mostly gone away but there are a few hanging around.