Hanta virus structure, illustration. Hantavirus is a respiratory disease carried in wild rodents such as deer mice. Mice do not appear ill while carrying the hantavirus. People become infected after breathing airborne particles of urine, droppings or saliva from infected rodents. Hantavirus causes flu-like symptoms that eventually cause the lungs to fill with fluid, making breathing difficult. Medical attention must be sought as soon as infection is detected. Most cases of Hantavirus reported in the U.S. have been in the rural Western states.