Hantavirus is a rare but extremely serious illness caused by a family of viruses known as hantaviruses. The first cases in the United States were diagnosed in southwestern states in 1993. Hantavirus disease is now being diagnosed in many other parts of the country and several different types of hantaviruses have been identified. Hantavirus is carried by infected wild rodents, primarily deer mice. The virus, which is found in the animal's urine, saliva and droppings, gets in the air as mist or dust that can be inhaled. The virus can infect the lungs and result in hantavirus pulmonary syndrome, which can be fatal.