Hantavirus, Salmonella, and Leptospirosis are just some of the dangerous diseases carried by rodents. A mouse or rat does not have to bite you in order for you to contract a disease. Urine, droppings and saliva from rodents all contain disease-causing germs which can also make their way into the air, resulting in problems with asthma and other allergic reactions.
Rats and mice may be small, but they'll make themselves known in various ways. Some signs you might have an infestation include: