Foot and mouth disease. Sheep standing by a sign warning of an outbreak of foot and mouth disease. This disease is caused by several viruses in the picornavirus group. It infects domestic and wild cloven-hooved animals, causing fever followed by the development of blisters in the mouth and on the feet. It is highly contagious, spreading by direct contact with infected animals and animal products, in the air and on materials that have been exposed to infection. Diseased areas are quarantined to avoid further spread, and infected farm animals are slaughtered and burnt to remove contamination. Photographed at the Northumberland Nature Park, England in 2001.