title: The phylogeographic pattern of Francisella tularensis in Sweden indicates a Scandinavian origin of Eurosiberian tularaemia.
abstract: Previous studies of the causative agent of tularaemia, Francisella tularensis have identified phylogeographic patterns suggestive of environmental maintenance reservoirs. To investigate the phylogeography of tularaemia in Sweden, we selected 163 clinical isolates obtained during 1995-2009 in 10 counties and sequenced one isolate's genome to identify new genetic markers. An improved typing scheme based on two indels and nine SNPs was developed using hydrolysis or TaqMan MGB probe assays. The results showed that much of the known global genetic diversity of F. tularensis subsp. holarctica is present in Sweden. Thirteen of the 163 isolates belonged to a new genetic group that is basal to all other known members of the major genetic clade B.I, which is spread across the Eurosiberian region. One hundred and twenty-five of the 163 Swedish isolates belonged to B.I, but individual clades' frequencies differed from county to county (P < 0.001). Subsequent analyses revealed a correlation between genotype variation over time and recurrent outbreaks at specific places, supporting the 'maintenance reservoir' environmental maintenance hypothesis. Most importantly, the findings reveal the presence of diverse source populations of F. tularensis subsp. holarctica in Sweden and suggest a historical spread of the disease from Scandinavia to other parts of Eurosiberia.
authors.affiliation: CBRN Defence and Security, Swedish Defence Research Agency, SE-90182 Umeå, Sweden.
authors.forename: Edvin
authors.initials: E
authors.lastname: Karlsson
authors.forename: Kerstin
authors.initials: K
authors.lastname: Svensson
authors.forename: Petter
authors.initials: P
authors.lastname: Lindgren
authors.forename: Mona
authors.initials: M
authors.lastname: Byström
authors.forename: Andreas
authors.initials: A
authors.lastname: Sjödin
authors.forename: Mats
authors.initials: M
authors.lastname: Forsman
authors.forename: Anders
authors.initials: A
authors.lastname: Johansson
mesh_terms: D015373:Bacterial Typing Techniques; D001483:Base Sequence; D005604:Francisella tularensis / Q000145:classification* / Q000235:genetics*; D014644:Genetic Variation; D016680:Genome, Bacterial / Q000235:genetics; D005838:Genotype; D006801:Humans; D058974:Phylogeography; D012537:Scandinavian and Nordic Countries; D013548:Sweden; D013997:Time Factors; D014406:Tularemia / Q000382:microbiology* / Q000473:pathology