Francisella Tularensis Clades B.FTN002-00 and B.13 Are Associated With Distinct Pathology in the European Brown Hare (Lepus europaeus)

Abstract

Tularemia is a severe disease caused by Francisella tularensis This bacterium has a major pathogenic potential in countless animal species as well as in humans. Despite the relatively significant body of literature available on this microorganism, many questions are still open concerning its biological cycle in the environment, the pathology and pathogenesis of the disease, the possible routes of infection in animals, and the pathologic and ecological relevance of the distinct phylogenetic clusters of F. tularensis In order to address these questions, we have thoroughly characterized the pathology and microbiology of terminally ill European brown hares (Lepus europaeus) infected with F. tularensis subsp. holarctica, collected in Switzerland from 2012 to 2014. F tularensis isolates were typed by defining their phylogenetic clusters. We showed that the pathology associated with F. tularensis subsp. holarctica belonging to the clade B.FTNF002-00 is different from that previously reported to be associated with the clade B.13. In particular, strains of the clade B.FTNF002-00 were almost invariably associated with splenitis and hepatitis and not with the polyserositis affecting pleura, pericardium, and kidney reported in the literature for infections caused by the clade B.13. We describe findings suggesting that the ports of entry for the bacteria might be the respiratory and digestive routes.

Tularemia in Germany—A Re-emerging Zoonosis

“…Both Francisella biovars are present in Germany (Tomaso et al, 2017 ). It is still under debate whether strains of genotype B.6 may have a higher pathogenic potential than strains belonging to the B.12 genotype (Gyuranecz et al, 2010 ; Origgi and Pilo, 2016 ; Hestvik et al, 2017 ; Kreizinger et al, 2017 ). There are further publications describing the phylogeographic pattern of Francisella in Europe (Vogler et al, 2009a ; Gyuranecz et al, 2012 ; Karlsson et al, 2013 ; Origgi et al, 2014 ; Thelaus et al, 2014 ; Dwibedi et al, 2016 ).…”

Phylogenetic Lineages of Francisella tularensis in Animals

“…F. tularensis subsp. holarctica was isolated from L. europaeus in many countries (Morner et al, 1988b ; Gyuranecz et al, 2010 ; Decors et al, 2011 ; Müller et al, 2013 ; Rijks et al, 2013 ; Nordstoga et al, 2014 ; Origgi and Pilo, 2016 ; Hestvik et al, 2017 ). In Sweden, the first animal tularemia case was diagnosed in 1931 in the mountain hare (Hestvik et al, 2017 ).…”

“…However, Origgi and Pilo found that the most affected organs in L. europaeus infected with F. tularensis subsp. holarctica lineage B.FTNF002-00 [B.6, subgroup B18, this subgroup is specific to Western Europe (Dwibedi et al, 2016 )] were the spleen and the liver (Origgi and Pilo, 2016 ). It has to be mentioned that the hares investigated by Gyuranecz and colleagues were hunted, while the hares investigated by Origgi and Pilo were terminally-ill.…”

Case of the month: What’s your diagnosis?

“…The absence of gross organ lesions in the current case is rather unusual, according to pathological findings of 28 brown hares diagnosed with tularemia in Switzerland (collected 2012-2014). Necropsy of those animals revealed splenomegaly in all 28 animals, lesions of the tracheal mucosa in 25 and lymphadenomegaly in 15 animals 7 . Histopathology of the current case, however, showed typical lesions for tularemia, such as multiple necrotic foci in liver, spleen and lymph nodes, which correlated with the obtained positive bacteriological results.…”