FIG. 7.

Mismatch distributions of the Kenya-1 and Kenya-2 lineage S, M, and L RVF virus genome segments. In each panel, the mismatch distributions of the Kenya-1 lineage are depicted on the left, with the Kenya-2 mismatch distributions depicted on the right. The actual observed frequencies of nucleotide (nt) substitutions between unique haplotypes are depicted in blue with diamond data markers. Simulated data of recent exponential population demographic expansion are depicted in red with square data markers. Analyses of the S segment were clearly unimodal for lineage Kenya-1, allowing for the rejection of the null hypothesis of stable population size and spatial expansion (P = 0.57 and 0.61, respectively) and providing evidence that an increase in virus population size and spatial distribution had occurred. Mismatch distributions for lineage Kenya-1 based on the M and L segments appeared to be multimodal, but no significant differences were found between the observed data and that simulated under a model of sudden expansion (M, P = 0.94 and 0.89; L, P = 0.70 and 0.62). Based on these results, the evidence of recent exponential population expansion prior to the 2006-2007 outbreak could not be ruled out for the S, M, and L RVF virus genome segments of the Kenya-1 lineage.