Epidemiology of Salmonella enterica Serovar Dublin in Cattle and Humans in Denmark, 1996 to 2016: a Retrospective Whole-Genome-Based Study

Abstract

Salmonella enterica serovar Dublin is a cattle-adapted S. enterica serovar causing both intestinal and systemic infection in its bovine host, and it is also a serious threat to human health. The present study aimed to determine the population structure of S. Dublin isolates obtained from Danish cattle herds and to investigate how cattle isolates relate to Danish human isolates, as well as to non-Danish human and bovine isolates. Phylogenetic analysis of 197 Danish cattle isolates from 1996 to 2016 identified three major clades corresponding to distinct geographical regions of cattle herds. Persistence of closely related isolates within the same herd and their circulation between epidemiologically linked herds for a period of more than 20 years were demonstrated. These findings suggest that a lack of internal biosecurity and, to some extent, also a lack of external biosecurity in the herds have played an important role in the long-term persistence of S. Dublin in Danish cattle herds in the period investigated. Global population analysis revealed that Danish cattle isolates clustered separately from bovine isolates from other countries, whereas human isolates were geographically spread. Resistance genes were not commonly demonstrated in Danish bovine isolates; only the isolates within one Danish clade were found to often harbor two plasmids of IncFII/IncFIB and IncN types, the latter plasmid carrying blaTEM-1, tetA, strA, and strB antibiotic resistance genes. IMPORTANCE S. Dublin causes economic losses in cattle production, and the bacterium is a public health concern. A surveillance and control program has been in place in Denmark since 2002 with the ultimate goal to eradicate S. Dublin from Danish cattle herds; however, a small proportion of herds have remained positive for many years. In this study, we demonstrate that herds with persistent infection often were infected with the same strain for many years, indicating that internal biosecurity has to be improved to curb the infection. Further, domestic cases of S. Dublin infection in humans were found to be caused both by Danish cattle isolates and by isolates acquired abroad. This study shows the strength of whole-genome sequencing to obtain detailed information on epidemiology of S. Dublin and allows us to suggest internal biosecurity as a main way to control this bacterium in Danish cattle herds.

Salmonella Derby: A Comparative Genomic Analysis of Strains From Germany

“…This could be because of the low prevalence of Salmonella in cattle in Germany (1%) ( BVL, 2019 ) and in Europe (3.86%) ( EFSA, 2018 ) compared with poultry and pigs. However, Salmonella in cattle has a significant zoonotic risk ( Hoelzer et al, 2011 ) of causing infections in humans ( Hsu et al, 2019 ; Kudirkiene et al, 2020 ). Besides, it causes economic losses because of mortality, and costs associated with infection control and treatment ( Hoelzer et al, 2011 ; Hsu et al, 2019 ).…”

Revisiting Persistent Salmonella Infection and the Carrier State: What Do We Know?

“…There does not appear to be any genomic evidence indicating that strains of S . Typhi associated with carriers are different to those in the wider population with both showing considerable variation in the core genome [ 112 , 130 ]. There also seems to be no association between phylogeny and persistence in S .…”

“…There also seems to be no association between phylogeny and persistence in S . Dublin [ 130 , 131 ]. Historically, S. Pullorum strains have existed in four major lineages [ 132 ] with two currently predominating [ 133 ] and with new CRISPR types appearing since 2001, this suggests continued evolution.…”

Comparison of cell invasion, macrophage survival and inflammatory cytokines profiles between Salmonella enterica serovars Enteritidis and Dublin from Brazil

“…Dublin is considered a health concern worldwide (CDC 2013; Kudirkiene et al . 2020). In Brazil, the available Salmonella reports are scarce and did not provide the serovar isolated, which make it difficult to compare the recent isolations of the serovars studied.…”

“…While S. Enteritidis is usually among the top Salmonella serovars isolated worldwide from human diarrohea, S. Dublin infections are not an usual causative agent of human infections. However, since it is highly pathogenic with high mortality rates, S. Dublin is considered a health concern worldwide (CDC 2013;Kudirkiene et al 2020). In Brazil, the available Salmonella reports are scarce and did not provide the serovar isolated, which make it difficult to compare the recent isolations of the serovars studied.…”