Comparative pan-genomic analyses of Orientia tsutsugamushi reveal an exceptional model of bacterial evolution driving genomic diversity by Fleshman, A, Mullins, K, Sahl, J, Hepp, C, Nieto, N, Wiggins, K, Hornstra, H, Kelly, D, Chan, T, Phetsouvanh, R, Dittrich, S, Panyanivong, P, Paris, D, Newton, P, Richards, A, Pearson, T