Rodents in your property will likely want to stay away from you. However, rats can bite in defense if they feel threatened. This defensive bite is rare, but can have serious repercussions. Rat saliva in some species carries dangerous diseases such as leptospirosis and Hantavirus. In even more rare circumstances, bite victims may contract rat-bite fever or tetanus infections.
No matter what, always seek professional medical attention when you are experiencing symptoms from a rodent bite.