Genomic epidemiology of Campylobacter fetus subsp. venerealis from Germany

Abstract

Campylobacter fetus subsp. venerealis (Cfv) causes bovine genital campylobacteriosis (BGC), a World Organization for Animal Health (WOAH)-listed trade-relevant disease characterized by severe reproductive losses, such as infertility, early embryonic death and abortion in cattle. BGC has significant economic implications that have prompted several countries to adopt stringent eradication and surveillance measures to contain the disease. In Germany, there has been a low incidence of BGC cases over the past 28 years. This study aimed to illustrate the genomic diversity of German Cfv strains isolated from different federal states in Germany. This study analyzed 63 Cfv strains, collected between 1985 and 2015, by whole-genome sequencing and compared them with genome data of 91 international Cfv isolates. The phylogenetic analysis showed that the Cfv population is genetically conserved and has geographic clusters. In Germany, one phylogenetic lineage comprising all strains was identified. This German lineage was part of a subclade that probably emerged in the nineteenth century and diversified over time. The results of this study point to a non-recurrent cross-border introduction of Cfv in Germany. The BGC control interventions in Germany can be considered successful as no outbreaks were reported since 2015.

Keywords: Campylobacter fetus subsp. venerealis; Germany; ISCfe1; WGS; bovine genital campylobacteriosis; dairy cattle; genomic epidemiology.

Figure 1

Distribution of reported outbreaks of bovine genital campylobacteriosis (BGC) in Germany over the last 28 years. (A) Chronological distribution of the reported BGC outbreaks per German state with the annual cumulative number of outbreaks in the bar chart. The bottom panel shows the temporal distribution of C. fetus subsp. venerealis strains examined by whole-genome sequencing in each state. Underlined German states indicate that no strains were available for sequencing. (B) Map showing the geographical distribution of reported BGC outbreaks across Germany.

Figure 2

Population structure of C. fetus subsp. venerealis (Cfv) strains. (A) A contextual phylogenetic analysis of the 63 German Cfv strains (1985–2015) in the light of global data from 11 countries is extrapolated by a midpoint-rooted maximum likelihood (ML) phylogenetic tree of clade 1. The placement of clade 1 (red) in relation to the major clades of the parent C. fetus species is shown in the inset box as previously indicated (7). The descending lineages of the C. fetus subsp. venerealis clade were named hierarchically. The German lineage (lineage 1.1.1) is highlighted with thickened yellow colored branches. (B) A pruned phylogeny showing the country-level diversification of the German lineage into two main lineages and five sublineages and their geographic distribution. The five sublineages were labeled according to their major geographic distribution and the branches were colored accordingly. The color bar on the right of the phylogeny in (A, B) highlights the geographic origin of the strains, as indicated in the legend. The date of the internal nodes was estimated using BactDating, and the estimated date ranges were superimposed onto the phylogeny. Branches with bootstrap values >90% are marked with a red circle. The branch lengths are in substitutions per core genome site.