text below from http://www.victorpest.com/advice/rodents-101/rodent-dangers
Transporters of Pathogens & Parasites
Rodents harbor a wide range of parasites such as mites and ticks that carry lethal pathogens. Even without parasites, rodents can directly transmit deadly germs excreted in their urine and feces.
Planes, Trains, & Automobiles
Rodents fly with us, drive with us, and live on the ships, buses, and such that transport us and our food around the globe. A hitchhiking rodent with its hitchhiking parasites and pathogens can go from one end of the planet to another in the time it takes to fly aboard our super jets.
In one week’s time rodents produce hundreds of fecal pellets and deposit urine in thousands of areas. The pathogens may also be deposited via saliva and blood spewed during rodent fights. Finally, rodents shed their hair daily and lose an entire coat twice a year. In this way, millions of rodent hairs and hair fragments, possibly containing pathogens, are also deposited into our environment.
Inside our buildings where food, water, and harborage are readily available, rodents can breed prolifically. This results in tens or hundreds of rodents living and moving about in our homes. Disease organisms present within these populations can spread rapidly to infect areas, people, and pets.