Foot-and-mouth disease type O viruses exhibit genetically and geographically distinct evolutionary lineages (topotypes)

Serotype O is the most prevalent of the seven serotypes of foot-and-mouth d isease (FMD) virus and occurs in many parts of the world. The UPGMA method was used to construct a phylogenetic tree based on nucleotide sequences at the 3' end of the VPI gene from 105 FMD type O viruses obtained from sample s submitted to the OIE/FAO World Reference Laboratory for FMD. This analysi s identified eight major genotypes when a value of 15% nucleotide differenc e was used as a cut-off. The validity of these groupings was tested on the complete VP1 gene sequences of 23 of these viruses by bootstrap resampling and construction of a neighbour-joining tree. These eight genetic lineages fell within geographical boundaries and we have used the term topotype to d escribe them. Using a large sequence database, the distribution of viruses belonging to each of the eight topotypes has been determined. These phyloge netically based epidemiological studies have also been used to identify vir uses that have transgressed their normal ecological niches. Despite the hig h rate of mutation during replication of the FMD virus genome, the topotype s appear to represent evolutionary cul-de-sacs.