A One Health investigation of Salmonella enterica serovar Wangata in north-eastern New South Wales, Australia, 2016–2017

Abstract

Salmonella enterica serovar Wangata (S. Wangata) is an important cause of endemic salmonellosis in Australia, with human infections occurring from undefined sources. This investigation sought to examine possible environmental and zoonotic sources for human infections with S. Wangata in north-eastern New South Wales (NSW), Australia. The investigation adopted a One Health approach and was comprised of three complimentary components: a case–control study examining human risk factors; environmental and animal sampling; and genomic analysis of human, animal and environmental isolates. Forty-eight human S. Wangata cases were interviewed during a 6-month period from November 2016 to April 2017, together with 55 Salmonella Typhimurium (S. Typhimurium) controls and 130 neighbourhood controls. Indirect contact with bats/flying foxes (S. Typhimurium controls (adjusted odds ratio (aOR) 2.63, 95% confidence interval (CI) 1.06–6.48)) (neighbourhood controls (aOR 8.33, 95% CI 2.58–26.83)), wild frogs (aOR 3.65, 95% CI 1.32–10.07) and wild birds (aOR 6.93, 95% CI 2.29–21.00) were statistically associated with illness in multivariable analyses. S. Wangata was detected in dog faeces, wildlife scats and a compost specimen collected from the outdoor environments of cases’ residences. In addition, S. Wangata was detected in the faeces of wild birds and sea turtles in the investigation area. Genomic analysis revealed that S. Wangata isolates were relatively clonal. Our findings suggest that S. Wangata is present in the environment and may have a reservoir in wildlife populations in north-eastern NSW. Further investigation is required to better understand the occurrence of Salmonella in wildlife groups and to identify possible transmission pathways for human infections.

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

“…An additional 4 S. Wangata isolates were obtained from wildlife scats collected in parallel to the outbreak investigation. The epidemiological findings from this investigation have been reported in detail elsewhere [9]. These showed that indirect contact with bats/flying foxes, wild frogs and wild birds were statistically associated with human illness.…”

“…Ninety Australian S. Wangata isolates were included in this study, 84 of which were obtained during an outbreak investigation conducted between November 2016 and April 2017 [9]. An additional six isolates were included and were obtained from routine surveillance of food (n = 3) and humans (n = 3) in NSW.…”

“…Outbreak isolates were cultured from humans (n = 75), wildlife (n = 7), a companion animal (n = 1) and compost (n = 1) and originated from various locations across three Local Health Districts in north-eastern NSW (combined total area of 163, 857 km 2 ). Detailed descriptions of the sample collection and isolation methodology are available in our previous publication [9]. Briefly, human isolates were obtained from diagnostic laboratories which used standard protocols for isolating Salmonella from clinical (stool) samples.…”

“…A core single-nucleotide polymorphism (SNP) tree of all S. Wangata isolates, all publicly available reference Salmonella genomes, and seven draft genomes of serovars of interest was constructed. The serovars of interest consisted of: serovars commonly isolated from human samples in NSW (S. Birkenhead, S. Bovismorbificans, S. Infantis); serovars isolated from wildlife during the environmental investigation of S. Wangata (S. Birkenhead, S. Bovismorbificans, S. Chailey, S. Kiambu, S. Kottbus) [9]; and a serovar in Australia primarily transmitted from environmental sources (S. Mississippi). The details of reference genomes are given in S2 Table. Reads were trimmed using Trimmomatic 0.36 [14] to remove trailing end bases with a phred score <33.…”

“…In order to identify possible environmental and zoonotic pathways for infections of S. Wangata an investigation into this slow moving outbreak was conducted between November 2016 to April 2017 in north-eastern NSW [9]. The outbreak investigation had three components, with corresponding objectives: a case-control study to identify human risk factors for infection; animal and environmental sampling to determine if S. Wangata was present in the environment; and a phylogenomic analysis to explore the relatedness of human, animal and environmental isolates.…”