While many rodents will scatter when you turn on the lights, rats and mice can still bite. Rats will bite you if they feel threatened, even going so far to lunge. 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. Always seek professional medical attention when bit by a rat or mouse, especially when you exhibit symptoms.