Defined by CFT and now ELISA using antisera from guinea pigs. No cross reaction or cross immunity between serotypes.
FMDV was the first animal virus in which serotypes were discovered.
In 1922 French cattle which had recovered from the disease, and therefore had added value, were re-infected by sick animals imported from Germany.
The 2 serotypes were named Oise (O) and Allemagne (A).
C was a second German serotype.
Three serotypes from South African territories (SAT), are called SAT1, 2 and 3 and one from India is Asia-1.
O, A, C are still the most widespread.