Foot-and-mouth disease is a highly contagious infection caused by an aphthovirus, and is classified in the same family as poliovirus. The virus has infected animals, mainly ungulates, in Africa since ancient times and was probably brought to the Americas in the 19th century by imported livestock. Foot-and-mouth disease is rarely fatal, but the economic losses incurred by outbreaks in sheep and cattle herds can be high. The last occurrence of the disease in the US was in 1929, but as recently as 2001, several large outbreaks occurred throughout the UK and thousands of animals were killed and burnt.