Figure 3. Phylogenetic tree including genotype B3 strains of measles virus (MV) from Nigeria collected in 1997–1998 and 2003–2005 (boldface) and World Health Organization (WHO) reference strains of genotypes B3.1, B3.2, and B2 (italics). Measles strains were named as indicated in the legend to Figure 1. For all strains from 2003–2005, which have been published, the GenBank accession number is given in brackets. For all strains from 1997–1998, NIE had been used as a 3-letter code for the country (10). For the more recent strains, the official WHO 3-letter code NGA was used. The phylogenetic tree was calculated on the basis of the 450-nt region that codes for the C-terminus of the MV N protein by using MEGA4 software (24) and the neighbor-joining method (Kimura 2-parameter, 1,000 bootstraps). Scale bar indicates nucleotide substitutions per site.