Rat Bites can cause Rat Bite fever which is a disease that is caused by two different bacteria.
A disease that Rats can spread to humans is leptospirosis which is most commonly spread through Rats Urine.
leptospirosis can also be caused by inhaling or handling scat.
If you do get bitten by a rat you should seek medical attention because Rat Bite Fever can be fatal if you do infected with it.