Diagnosis and control of Salmonella Dublin in dairy herds

Social network analysis reveals the failure of between-farm movement restrictions to reduce Salmonella transmission

An increasing number of countries are investigating options to stop the spread of the emerging zoonotic infection Salmonella (S.) Dublin, which mainly spreads among bovines and with cattle manure. Detailed surveillance and cattle movement data from an 11-year period in Denmark provided an opportunity to gain new knowledge for mitigation options through a combined social network and simulation modeling approach. The analysis revealed similar network trends for non-infected and infected cattle farms despite stringent cattle movement restrictions imposed on infected farms in the national control program. The strongest predictive factor for farms becoming infected was their cattle movement activities in the previous month, with twice the effect of local transmission. The simulation model indicated an endemic S. Dublin occurrence, with peaks in outbreak probabilities and sizes around observed cattle movement activities. Therefore, pre- and post-movement measures within a 1-mo time-window may help reduce S. Dublin spread.

Review: Salmonella Dublin in dairy cattle

Salmonella enterica serovar Dublin (S. Dublin) is a bacterium host-adapted to cattle with increasing prevalence in dairy facilities. It can severely affect cattle health, producing high morbidity and mortality in young calves and reducing the performance of mature animals. Salmonella Dublin is difficult to control and eradicate from herds, as it can be shed from clinically normal animals. In addition, S. Dublin is a zoonotic bacterium that can be lethal for humans and pose a risk for human and animal health due to its multi-drug resistant characteristics. This review provides an overview of S. Dublin as a pathogen in dairy facilities, the risk factors associated with infection, and current strategies for preventing and controlling this disease. Furthermore, current gaps in knowledge are also discussed.

Cattle abortions update

This focus article has been prepared by Arthur Otter of the Cattle Expert Group at the APHA.

Confounding Role of Salmonella Serotype Dublin Testing Results of Boneless and Ground Beef Purchased for the National School Lunch Program, October 2013 to July 2017

ABSTRACT

The Agricultural Marketing Service procures boneless and ground beef for federal nutrition assistance programs. It tests procured beef for concentrations of standard plate counts (SPCs), coliforms, and Escherichia coli and for the presence of Salmonella and Shiga toxin-producing E. coli. Any lot exceeding predefined critical limits (100,000 CFU g-1 for SPCs, 1,000 CFU g-1 for coliforms, and 500 CFU g-1 for E. coli) or positive for Salmonella or Shiga toxin-producing E. coli is rejected for purchase. Between 1 October 2013 and 31 July 2017, 166,796 boneless beef lots (each approximately 900 kg) and 25,051 ground beef sublots (each approximately 4,500 kg) were produced. Salmonella was detected in 1,955 (1.17%) boneless beef lots and 219 (0.87%) ground beef sublots. Salmonella sample size increased from an individual 25-g sample to a co-enriched 325-g sample on 1 March 2015. Salmonella presence was associated with season (lowest in spring), larger sample size, and increased log SPC in boneless and ground beef. Increased log E. coli was associated with Salmonella presence in boneless beef, but not ground beef. Salmonella Dublin was the most common serotype in boneless beef (743 of 1,407, 52.8%) and ground beef (35 of 171, 20.5%). Salmonella Dublin was generally associated with lower indicator microorganism concentrations compared with other Salmonella serotypes as a group. Relative to other Salmonella, Salmonella Dublin was associated with season (more common in spring) and smaller sample size in boneless and ground beef. Decreased log SPCs and log coliforms were associated with Salmonella Dublin presence in boneless beef, but not in ground beef. Differential associations between Salmonella Dublin and other serotypes with indicator microorganisms were strong enough to cause confounding and suggest that the presence of Salmonella Dublin needs to be accounted for when evaluating indicator performance to assess Salmonella risk in boneless and ground beef.

HIGHLIGHTS

Geography Shapes the Population Genomics of Salmonella enterica Dublin

Salmonella enterica serotype Dublin (S. Dublin) is a bovine-adapted serotype that can cause serious systemic infections in humans. Despite the increasing prevalence of human infections and the negative impact on agricultural processes, little is known about the population structure of the serotype. To this end, we compiled a manually curated data set comprising of 880 S. Dublin genomes. Core genome phylogeny and ancestral state reconstruction revealed that region-specific clades dominate the global population structure of S. Dublin. Strains of S. Dublin in the UK are genomically distinct from US, Brazilian, and African strains. The geographical partitioning impacts the composition of the core genome as well as the ancillary genome. Antibiotic resistance genes are almost exclusively found in US genomes and are mediated by an IncA/C2 plasmid. Phage content and the S. Dublin virulence plasmid were strongly conserved in the serotype. Comparison of S. Dublin to a closely related serotype, S. enterica serotype Enteritidis, revealed that S. Dublin contains 82 serotype specific genes that are not found in S. Enteritidis. Said genes encode metabolic functions involved in the uptake and catabolism of carbohydrates and virulence genes associated with type VI secretion systems and fimbria assembly respectively.

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

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 bla _TEM-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.

Schmallenberg virus infection in Scottish cattle

Schmallenberg virus infection on cattle farms in southern ScotlandOutbreaks of infectious bovine rhinotracheitisSalmonella Bovismorbificans infection in cattle and sheepGastric ulceration in pigsTrichomonosis in a sparrowhawk and a hen harrierThese are among matters discussed in the disease surveillance report for April 2017 from SAC Consulting: Veterinary Services (SAC C VS).