Genomic characterisation of Salmonella enterica serovar Wangata isolates obtained from different sources reveals low genomic diversity.

Salmonella enterica serovar Wangata is an important pathogen in New South Wales (NSW), Australia. The incidence of S. Wangata is increasing and transmission is suspected to be via a non-food source. A recent outbreak investigation of sources of S. Wangata recovered isolates from humans, domestic animals, wildlife and the environment. Here, we extend that investigation by characterising and describing the genomic determinates of these isolates. We found that Australian S. Wangata isolates from different sources exhibited similar virulence and antimicrobial resistance gene profiles. There were no major genomic differences between isolates obtained from different geographical regions within Australia or from different host species. In addition, we found evidence (low number of SNPs and identical virulence gene profiles) suggestive of an international transmission event between Australia and the United Kingdom. This study supports the hypothesis that S. Wangata is shared between different hosts in NSW, Australia and provides strong justification for the continued use of genomic surveillance of Salmonella.

Divergent geography of Salmonella Wangata and Salmonella Typhimurium epidemiology in New South Wales, Australia.

Salmonella enterica serovar Wangata is an important cause of salmonellosis in the state of New South Wales, Australia. Standard surveillance has not identified a common food source and cases have been attributed to an unknown environmental or wildlife reservoir. Investigation of the spatial distribution of cases may provide valuable insights into local risk factors for infection and the potential role of the environment and wildlife. Using conditional autoregressive analysis, we explored the association between laboratory-confirmed cases of S. Wangata reported to the New South Wales Department of Health and human socio-demographic, climate, land cover and wildlife features. For comparison, a model was also fitted to investigate the association of cases of Salmonella enterica serovar Typhimurium, an established foodborne serotype, with the same features. To determine if cases of S. Wangata were associated with potential wildlife reservoir species, additional variables were included in the S. Wangata model that indicated areas of high suitability for each species. We found that cases of S. Wangata were associated with warmer temperatures, proximity to wetlands and amphibian species richness. In contrast, cases of S. Typhimurium were associated with human demographic features (proportion of the population comprising children <5 years old), climate (mean annual precipitation and mean annual temperature) and land cover (proportion comprising urban and evergreen broadleaf forest). These findings support the hypothesis that S. Wangata is likely to be associated with an environmental source. Whilst we expected S. Typhimurium to be associated with the human socio-demographic feature, the significance of the land cover features was surprising and might suggest the epidemiology of S. Typhimurium in Australia is more complex than currently understood.

Diversity of Salmonella serotypes from humans, food, domestic animals and wildlife in New South Wales, Australia.

BACKGROUND: Salmonella is an important human pathogen in Australia and annual case rates continue to increase. In addition to foodborne exposures, cases have been associated with animal and contaminated environment contact. However, routine surveillance in Australia has tended to focus on humans and food, with no reported attempts to collate and compare Salmonella data from a wider range of potential sources of exposure. METHODS: Salmonella data from humans, food, animals and environments were collated from a range of surveillance and diagnostic sources in New South Wales (NSW). Data were categorised to reflect one of 29 sample origins. Serotype diversity was described for each category, and the distribution of serotypes commonly isolated from humans was examined for each sample origin. The distribution of serotypes along the livestock-food-human continuum and at the companion animal-wildlife interface was also examined. RESULTS: In total, 49,872 Salmonella isolates were included in this analysis, comprising 325 serotypes. The vast majority of these isolates were from humans (n = 38,106). Overall S. Typhimurium was the most frequently isolated serotype and was isolated from all sample categories except natural environment and game meat. S. Enteriditis was not isolated from any livestock animal, however sporadic cases were documented in food, companion animals and a reptile. Many serotypes that were frequently isolated from livestock animals and associated food products were only rarely isolated from humans. In addition, a number of key human serotypes were only sporadically isolated from livestock and food products, suggesting alternative sources of infection. In particular, S. Paratyphi B Java and S. Wangata were more often isolated from wild animals. Finally, there was some overlap between serotypes in companion animals and wildlife, with cats in particular having a large number of serotypes in common with wild birds. CONCLUSIONS: This is the most comprehensive description of Salmonella data from humans, food, livestock, wildlife, companion animals and various environments in Australia reported to date. Results confirm that livestock and food are important sources of salmonellosis in humans but that alternative sources - such as contact with wildlife and environments - warrant further investigation. Surveillance in NSW is largely human-focussed: major knowledge gaps exist regarding the diversity and frequency of serotypes in animals. More systematic surveillance of domestic animals and wildlife is needed to inform targeted control strategies and quantitative source attribution modelling in this state.