The sub-type classification of strains of foot-and-mouth disease virus.

Sixteen foot-and-mouth disease virus (FMDV) strains of type SAT 1 were compared in complement-fixation tests. With the test used, the range of antigenic variation within a type appeared to be greater than previously described. The concept of a sub-type group within which all strains are more closely related to each other than to any strain outside the group was not supported. Considering the group of strains studied, it is suggested that the classification of strains is best achieved by moninating a reference strain for each sub-type. Others are classified as related strains in one or more sub-type groups according to their relationships with the reference strains.