If you have one, you probably have a bunch.
Poison the heck out of them, and get the good stuff from a farm store, not DCon. If you can get hold of a product called Golden Malrin Flybait, that's the best stuff, but don't let any pets near it.
Piles of junk, wood piles, clutter, old buildings, etc. are magnets for rats. If you or your neighbors have these conditions and / or any type of animal feed or accessible garbage around it needs to be eliminated. When we bought our farm, there were several old falling down barns on the property, agricultural fields all around and they had previously had livestock (feed) on the property. We had rats until we got all of this stuff cleaned up, burned, buldozed and buried the old barns, cleaned up the property, kept animal feed in steel containers, etc., etc.