Phylogeographic Distribution of Human and Hare Francisella Tularensis Subsp. Holarctica Strains in the Netherlands and Its Pathology in European Brown Hares (Lepus Europaeus).

Miriam Koene,Miriam Maas,Maaike De Vries,Ewout Fanoy,Robin Ruuls,Andrea Gröne,Peter Van Tulden,Marja Kik,Malin Granberg,Jooske Ijzer,Herjan Bavelaar,Mats Forsman,Marc Engelsma,Marcel Spierenburg,Roan Pijnacker,Hanneke Berkhout,Hendrik Jan Roest ,Jolianne M Rijks ,Daan W Notermans ,R.j.a Diepersloot ,Sanjay U C Sankatsing ,Kerstin Myrtennäs

doi:10.3389/fcimb.2019.00011

Abstract

Sequence-based typing of Francisella tularensis has led to insights in the evolutionary developments of tularemia. In Europe, two major basal clades of F. tularensis subsp. holarctica exist, with a distinct geographical distribution. Basal clade B.6 is primarily found in Western Europe, while basal clade B.12 occurs predominantly in the central and eastern parts of Europe. There are indications that tularemia is geographically expanding and that strains from the two clades might differ in pathogenicity, with basal clade B.6 strains being potentially more virulent than basal clade B.12. This study provides information on genotypes detected in the Netherlands during 2011–2017. Data are presented for seven autochthonous human cases and for 29 European brown hares (Lepus europaeus) with laboratory confirmed tularemia. Associated disease patterns are described for 25 European brown hares which underwent post-mortem examination. The basal clades B.6 and B.12 are present both in humans and in European brown hares in the Netherlands, with a patchy geographical distribution. For both genotypes the main pathological findings in hares associated with tularemia were severe (sub)acute necrotizing hepatitis and splenitis as well as necrotizing lesions and hemorrhages in several other organs. Pneumonia was significantly more common in the B.6 than in the B.12 cases. In conclusion, the two major basal clades present in different parts in Europe are both present in the Netherlands. In hares found dead, both genotypes were associated with severe acute disease affecting multiple organs. Hepatitis and splenitis were common pathological findings in hares infected with either genotype, but pneumonia occurred significantly more frequently in hares infected with the B.6 genotype compared to hares infected with the B.12 genotype.

Highlights

Tularemia, caused by the bacterium Francisella tularensis, may be regarded as a relatively new disease in Western Europe
F. tularensis subsp. holarctica strains from five patients were assigned to basal clade B.6, the remaining two cases the strains were assigned to B.12 (Table 1)
In one of the B.12 cases an isolate was available for WGS and using the CanSNPer pipeline was found to belong to B.33 which is a subgroup of B.20

Summary

Introduction

Tularemia, caused by the bacterium Francisella tularensis, may be regarded as a relatively new disease in Western Europe. In the late 1930s the disease was first reported in (current) Austria, and additional outbreaks were described in following decades from several other countries like Germany, France, and Belgium (Jusatz, 1952). In Europe, disease is almost exclusively caused by F. tularensis subsp. A first set of canonical SNPs (canSNPs), representing key positions along the Francisella phylogenetic tree were identified and labeled by serial numbers (Svensson et al, 2009; Vogler et al, 2009) and the resulting phylogenetic structure is still the basis for the current nomenclature for F. tularensis subsp. A first set of canonical SNPs (canSNPs), representing key positions along the Francisella phylogenetic tree were identified and labeled by serial numbers (Svensson et al, 2009; Vogler et al, 2009) and the resulting phylogenetic structure is still the basis for the current nomenclature for F. tularensis subsp. holarctica genotypes; an acronym using the letter “B” for the subspecies holarctica, and for subclades the characters “Br.” followed by the branch numbers named for the two flanking canSNPs (for instance B.Br.010/011), or the designated identification of a reference strain (for instance B.Br.FTNF002-00)

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Discussion

Conclusion