Foot-and-mouth disease (FMD) is the most contagious disease of cloven-hoofed animals. The disease is highly infectious and is characterized by rapid transmission, a sequel to the rather explosive growth cycle of the causative virus, FMDV (an aphthovirus; Picornaviridae). As few as 10–25 virus particles can establish air-borne infection in domestic ruminants and pigs. The latter emit the greatest amounts of virus as aerosols. In unvaccinated herds mortality can be high, particularly in young cattle and pigs. Milk production ceases and animals used for traction can become useless. Internationally agreed policy dictates that once a country has adopted an eradication strategy, all animals on affected farms must be destroyed. In areas where the disease occurs, trade of livestock and animal products must be blocked, and a wide range of agricultural products may be banned from export to other countries.