Do rats carry hanta virus, or only the bubonic plague? Filthy bast'rds they are! I'd hit them with everything you've got... poison, traps (inside and out), and pellet gun or .22 if your location allows it. They have to have some kind of food source. The infestations I've heard of around here have been the result of bird or pet feeding practices. I read that bird feed mixed with peanut butter was a good trap bait. Run up a BIG body count and post trophy pictures.