Figure. NSs-based phylogenetic tree of Rift Valley fever virus strains. Values indicate the bootstrap support of the nodes. Strains isolated in Chad are designated H1CHA01 and H2CHA01, according to the previous abbreviation guidelines (7,8). EMBL accession nos. AJ504997 and AJ504998. SNS, Smithburn strain. Branch lengths are proportional to the number of substitutions per site.