Introduction and persistence of tularemia in Bulgaria

Abstract

IntroductionOutbreaks of the zoonotic disease tularemia occurred in north-east Bulgaria in the 1960s. Then came 30 years of epidemiological silence until new outbreaks occurred in west Bulgaria in the 1990s. To investigate how bacterial strains of Francisella tularensis causing tularemia in wildlife and humans in the 1960s and the 1990s were related, we explored their genetic diversity.Material and methodsTen F. tularensis genomes from the 1960s (n=3) and the 1990s (n=7) were sequenced, assigned to canonical single-nucleotide polymorphism (canSNP) clades, and compared to reference genomes. We developed four new canSNP polymerase chain reaction (PCR) assays based on the genome sequence information.Results and discussionThe genetic analysis showed that the outbreaks in the 1960s as well as in the 1990s involved multiple clones and new genetic diversity. The smallest genetic difference found between any of the Bulgarian strains was five SNPs between the strains L2 and 81 isolated 43 years apart, indicating that F. tularensis may persist locally over long time periods without causing outbreaks. The existence of genetically highly similar strain-pairs isolated the same year in the same area from different hosts supports a hypothesis of local expansion of clones during outbreaks. Close relationship (two SNPs) was found between one strain isolated 1961 in northeast Bulgaria and one strain isolated 5 years before in USSR. Historical data coinciding with the actual time point describe the introduction of water rats from USSR into the Bulgarian outbreak area, which may explain the close genetic relationship and the origin of the outbreak.ConclusionGenome analysis of strains from two outbreaks in the 1960s and the 1990s provided valuable information on the genetic diversity and persistence of F. tularensis in Bulgaria.

Russian isolates enlarge the known geographic diversity of Francisella tularensis subsp. mediasiatica

“…Whole genome sequencing will help investigate more precisely the population structure of the M.II group, as illustrated by the investigation of other F . tularensis foci [ 40 ] and the evolutionary relationships between subsp. mediasiatica , holarctica and tularensis .…”

Phylogenetic Lineages of Francisella tularensis in Animals

“…These studies led to the discovery of a very precise and vast amount of sublineages derived from basal lineages. As a consequence, the cladistic nomenclature was particularly detailed in the recent years (Chanturia et al, 2011 ; Hansen et al, 2011 ; Vogler et al, 2011 ; Gyuranecz et al, 2012 ; Karlsson et al, 2013 ; Müller et al, 2013 ; Origgi et al, 2014 ; Wang et al, 2014 ; Karadenizli et al, 2015 ; Kilic et al, 2015 ; Sissonen et al, 2015 ; Dwibedi et al, 2016 ; Myrtennas et al, 2016 ; Schulze et al, 2016 ).…”

“…Branch length is not representative of evolutionary distance and is not scaled. Data presented in this figure was collected and assembled from the following publications: (Farlow et al, 2001 ; Abril et al, 2007 ; Fujita et al, 2008 ; Svensson et al, 2009b ; Vogler et al, 2009 ; Chanturia et al, 2011 ; Gyuranecz et al, 2012 ; Müller et al, 2013 ; Origgi et al, 2014 ; Elashvili et al, 2015 ; Sissonen et al, 2015 ; Dwibedi et al, 2016 ; Myrtennas et al, 2016 ; Schulze et al, 2016 ; Eden et al, 2017 ).…”

Tularemia as a cause of lymphadenopathy in adults and children

“…Болгарские ученые установили связь вспышки туляремии в 1960-е гг. с доставленными из СССР ондатрами [8]. Проблема туляремии в Европе осложняется и тем, что не существует европейской вакцины для профилактики этой болезни.…”