Investigation of the increase of swine erysipelas in Ontario (OAHN 009115)
Đurđa Slavić, Daniel Bogema, Tim Pasma, Narelle Sales, Ian Marsh, Sue Burlatschenko and Josepha DeLay
Animal Health Laboratory, University of Guelph, Guelph, ON (Slavić, DeLay); Elizabeth Macarthur Agricultural Institute, New South Wales, Australia (Bogema, Marsh, Sales); Goshen Ridge Veterinary Services, Tillsonburg, ON (Burlatschenko), Ontario Ministry of Agriculture and Rural Affairs (Pasma).
AHL Newsletter 2020;24(3):8.
Since the fall of 2015, the OAHN Swine Network has noted an increase in activity of swine erysipelas, based on data from practitioners completing the quarterly survey and from provincial and federal slaughter plants. The purpose of this study was to isolate and, using whole genome sequencing (WGS), to characterize isolates of swine erysipelas from abattoirs and swine farms in Ontario. During 2019, tissue samples (e.g., lung and spleen) collected from hogs in slaughterhouses and clinical cases in Ontario with lesions suspicious for swine erysipelas were submitted to Animal Health Laboratory (AHL) for culture. In total, 8 cases were received comprised of 25 samples. Eleven samples were collected from clinical cases whereas 14 samples were from slaughterhouses.
Only 6 isolates of Erysipelothrix rhusiopathiae were recovered from the samples submitted (3 from the clinical cases), even though enrichment method was used for culturing. This low recovery of isolates can potentially be explained by previous antimicrobial treatment, chronic course of the disease or possibility of other septic causes with cutaneous involvement resembling E. rhusiopathiae. To compensate for low number of isolates recovered, E. rhusiopathiae isolates conveniently archived by the AHL (5) and Gallant Custom Laboratories (3) were also included in the study, bringing the total number of isolates for sequencing to 14. Based on limited data available for each isolate, it is likely that isolates originated from 11 different premises; however, this cannot be confirmed. Most of the sequenced isolates were archived isolates recovered in 2015 (1), 2016 (2) and 2018 (5).
Isolates were sequenced using Illumina MiSeq and whole genome sequence data were used to detect the resistance genes, virulence genes and to establish multi locus sequence types (MLST) of Ontario isolates. The MLST was done by analyzing 7 housekeeping genes. As no E. rhusiopathiae MLST scheme is available in a public MLST database, sequence types (ST) were randomly assigned to each isolate, indicating that there are 8 different MLSTs present among 14 isolates. When comparing MLST of Ontario isolates to a MLST scheme developed by an Australian research group, it was determined that only 2 of Ontario isolates belong to the existing ST4. All other STs were new and were assigned ST from 110 to 116 (Fig. 1).
The presence of antimicrobial resistance genes was not detected in all Ontario isolates, but when detected, resistance to tetracyclines and lincosamides was consistently present. In addition, most of the isolates sequenced in this study had all putative virulence genes as defined previously.
Because of the limited number of isolates, all data presented here are considered preliminary and more work is needed before any solid conclusions can be drawn. Our data indicate that isolates from the same premises are likely uniform as they have the same MLST, AMR and virulence genes patterns. Similar to other studies, a significant diversity in MLST was observed for Ontario isolates with the newly detected MLSTs. However, there are some indications that, in general, isolates from the same geographical locations tend to cluster together (Fig. 1). To confirm this hypothesis, more isolates from Ontario need to be sequenced and included in the MLST database in order to monitor their epidemiological relatedness. From the clinical perspective, there is currently no correlation between a specific MLST and virulence potential of the isolate. AHL
Figure 1. The full MLST location image is a complete minimum spanning tree of all the isolates, with node colours representing continents (Europe - Green; Australia - Blue; North America - Red; Asia - Purple; South America - Teal; NA - Grey). Ontario isolates belongs to ST4, ST110, ST111, ST112, ST113, ST114, ST115, and ST116. Courtesy of D. Bogema, Elizabeth Macarthur Agricultural Institute, NSW.
References
1. Janßen T et al. A combinational approach of multilocus sequence typing and other molecular typing methods in unravelling the epidemiology of Erysipelothrix rhushiopathiae strains from poultry and mammals. Vet Res 2015; DOI 10.1186/s13567-015-0216-x.
2. Ogava Y et al. The genome of Erysipelothrix rhusiopathiae, the causative agent of swine erysipelas, reveals new insights into the evolution of Firmicutes, and the organism’s intracellular adaptations. J Bact 2011;193;2959-2971.
3. Sales N et al. Innovation Grant: 2A-117 – Erysipelothrix rhusiopathiae Epi-interface, a new approach to the management of porcine erysipelas. 2018.