Hantavirus: A group of viruses that cause hemorrhagic fever and pneumonia. The Hantaviruses include the Hantaan virus that causes Korean (and Manchurian) hemorrhagic fever. The Hantavirus Pulmonary Syndrome (HPS) struck the Four Corner area (where the States of Arizona, New Mexico, Colorado, and Utah meet) in 1993 with devastating, frequently fatal consequences. Hantaviruses are transmitted to humans by contact direct or indirect with the saliva and excreta of rodents such as deer mice, field mice, and ground voles. The HPS outbreak in 1993 followed two years in which there was more rain, more foliage, and more deer mice than usual.