Phylogeography of Francisella tularensis subsp. holarctica, Europe

Miklós Gyuranecz¹, Dawn N. Birdsell¹, Wolf Splettstoesser, Erik Seibold, Stephen M. Beckstrom-Sternberg, László Makrai, László Fodor, Massimo Fabbi, Nadia Vicari, Anders Johansson, Joseph D. Busch, Amy J. Vogler, Paul Keim, and David M. Wagner

Author affiliations: Hungarian Academy of Sciences, Budapest, Hungary (M. Gyuranecz); Northern Arizona University, Flagstaff, Arizona, USA (D.N. Birdsell, J.D. Busch, A.J. Vogler, P. Keim, D.M. Wagner); Bundeswehr Institute of Microbiology, Munich, Germany (W. Splettstoesser, E. Seibold); Translational Genomics Research Institute, Phoenix, Arizona, USA (S.M. Beckstrom-Sternberg, P. Keim); Szent István University, Budapest (L. Makrai, L. Fodor); Istituto Zooprofilattico Sperimentale della Lombradia e dell’Emilia Romagna, Pavia, Italy (M. Fabbi, N. Vicari); Umeå University, Umeå, Sweden (A. Johansson)

Abstract

Francisella tularensis subsp. holarctica isolates from Austria, Germany, Hungary, Italy, and Romania were placed into an existing phylogeographic framework. Isolates from Italy were assigned to phylogenetic group B.FTNF002–00; the other isolates, to group B.13. Most F. tularensis subsp. holarctica isolates from Europe belong to these 2 geographically segregated groups.

Francisella tularensis is the etiologic agent of tularemia and a highly virulent category A biothreat agent (1,2). The most widely distributed subspecies is F. tularensis subsp. holarctica, which is found throughout much of the Northern Hemisphere and is the only subspecies found in Europe (3). Despite its wide geographic distribution, F. tularensis subsp. holarctica contains low genetic diversity, which indicates recent emergence (4). A recent global phylogeographic analysis (5), and several subsequent analyses (6–9), assigned most isolates from Europe to 2 phylogenetic groups: B.FTNF002–00 and B.13 (includes multiple subclades descended from branch B.13 [5,6,8]; branch and subclade nomenclature from [5] has been shortened by removing Br and extra 0s from individual branch and subclade names). These groups appear to be geographically segregated: only isolates from B.FTNF002–00 have been reported from the western European countries of Spain, France, and Switzerland, whereas B.13 is the only or dominant type reported from the Czech Republic, Finland, Georgia, Russia, Slovakia, and Ukraine (5–9). We provide additional information about the geographic distribution of these 2 groups using existing phylogenetic signatures (5,8) to place 45 isolates from Austria, Germany, Hungary, Italy, and Romania (Table A1) into the existing global phylogeographic framework.