Hanta virus, a distant cousin of the Ebola virus, has been recognized as a cause of disease for many years. In the United States, disease caused by Hanta virus has probably always existed, but in such low numbers that it was not recognized.
A 1993 outbreak of fatal respiratory illness on an Indian reservation in the Four Corners area (the border of Utah, Colorado, New Mexico, and Arizona) led epidemiologists to the discovery of Hanta virus as the causative agent. Since that discovery, Hanta virus disease has been reported in every western state, and in many eastern states.
Hanta virus is carried by rodents, particularly deer mice, and is present in their urine and feces. The Hanta virus does not cause disease in the carrier animal, but it does in man. Humans are thought to become infected when they are exposed to contaminated dust from the nests or droppings of mice.
The disease is not, however, passed between humans. Contaminated dust is often encountered when cleaning long-vacated dwellings, sheds, or other enclosed areas.
The federal Centers for Disease Control and Prevention (CDC) reported that rodents carrying Hanta virus have been found in at least twenty national parks and that it is possible that the virus is in all of the parks.