The intelligent rats expanded fast after getting out of the lab.  They smuggled themselves on trucks, trains, planes, and ships bound for pretty much anywhere.  And they bred like…well…rats.  I never really saw them where I grew up.  Northern Minnesota is too cold for anything that small to stay by choice.  They really loved Washington DC though.  New York too.  I’ve met a few New York rats, and let me tell you, they are nuts.