There are seven immunologically distinct serotypes of the foot-and-mouth disease (FMD) virus and over 60 subtypes. The seven serotypes are A, C, O, Asia 1, SAT 1, SAT 2, and SAT 3. New subtypes occasionally develop spontaneously. The large number of virus types and subtypes creates challenges for the maintenance of vaccine stockpiles that can be deployed in the event of an outbreak.
Strains of FMD serotype O are of most concern for disease spread into new areas. FMD serotype O (specifically, type O pan Asia strain) was responsible for the 2001 United Kingdom outbreak and has been tied to recent FMD incursions in previously unaffected regions worldwide. In 2010 and 2011, these have variously included Botswana, Bulgaria, China, India, Israel, Japan, Kazakhstan, Mongolia, Mozambique, Myanmar, Nigeria, North Korea, Paraguay, Russia, South Africa, South Korea, Taiwan, Vietnam, Zambia, and Zimbabwe.