Genomic Epidemiology and Management of Salmonella in Island Ecosystems Used for Takahe Conservation

Prevalence of Salmonella spp. in translocated wild reptiles and effect of duration of quarantine on their body condition

AIMS

To assess the prevalence of carriage of Salmonella spp. in wild reptiles translocated from multiple locations to a single island, and determine changes in their body condition (BC) during quarantine.

METHODS

Between 2007 and 2009, six endemic reptile species (Oligosoma aeneum, O. moco, O. ornatum, O. smithi, Dactylocnemis pacificus, and Woodworthia maculata) were caught from several locations in the northern North Island of New Zealand. Reptiles were held in quarantine for 14-41 days while being tested for carriage of Salmonella spp. Morphometric data were collected, and scaled body mass index for each species was calculated to determine changes in BC during the quarantine.

RESULTS

Of 221 individuals tested 12 (5%) were positive for Salmonella spp. All 12 were shore skinks (O. smithi; n = 30), with a test prevalence of 0.4 (95% CI = 0.25-0.58). Eleven were carrying Salmonella enterica Warragul and one S. enterica Mississipi. There was no difference in BC at the start of quarantine of shore skinks between those that tested negative and those that tested positive for Salmonella spp. (p = 0.184). Reptiles that were quarantined for 15-20 days (three species) lost 3-5% of BC (mean proportional change 0.03-0.05), while those quarantined for >30 days increased BC by 3-13% (mean proportional change 0.03-0.13). All animals except the one individual positive for S. Mississippi were translocated to the recipient island, while the latter was returned to the source site.

CONCLUSIONS AND CLINICAL RELEVANCE

The prevalence of Salmonella spp. carriage in the translocated reptiles was low overall and consistent with other records of Salmonella spp. in wild New Zealand reptiles. However, the prevalence of 0.4 in shore skinks is the highest recorded in this species. In addition to time required for health-screening, we recommend that duration of quarantine should include time to allow animals to recover from captive stress and to provide an opportunity to increase their BC before release.

Salmonella from a Microtidal Estuary Are Capable of Invading Human Intestinal Cell Lines

Faecal contamination poses health risks for the recreational users of urban estuaries. However, our understanding of the potential pathogenicity of faecal microbes in these environments is limited. To this end, a study was conducted to understand the spatial and seasonal distribution of Salmonella in water and sediments of the Yarra River estuary, Melbourne, Australia. Among 210 samples in total, culturable Salmonella were recovered from 27%, 17%, and 19% of water, bank, and bed sediment samples, respectively. The combined detection increased from 15% in winter to 32% in summer (p < 0.05) indicating seasonal variation as potential part of public health risk assessments. Further, pathogenic potential of the Salmonella isolates was characterised via the quantification of attachment and invasion capacity using human epithelial colorectal cell line Caco-2 on a subset of isolates (n = 62). While all of these isolates could attach and invade Caco-2 cells, 52% and 13% of these showed greater attachment and invasiveness, respectively, than the corresponding mean values for S. Typhimurium ATCC14028 control. Isolates from winter were on average more invasive (seven out of eight isolates with the highest invasiveness recovered from the colder sampling period) than the isolates from summer, and Salmonella collected during summer showed lower invasion (p < 0.05) compared with the control. Similar low invasion compared with the same control was observed for isolates recovered from bank sediment (p < 0.05). While the higher prevalence in summer may imply higher risks during these peak recreational periods, it is essential that this information is used in combination with quantitative microbial risk assessments to fully understand the health risks posed by Salmonella in microtidal estuaries.

Whole-Genome Sequencing of Salmonella Mississippi and Typhimurium Definitive Type 160, Australia and New Zealand

We used phylogenomic and risk factor data on isolates of Salmonella enterica serovars Mississippi and Typhimurium definitive type 160 (DT160) collected from human, animal, and environmental sources to elucidate their epidemiology and disease reservoirs in Australia and New Zealand. Sequence data suggested wild birds as a likely reservoir for DT160; animal and environmental sources varied more for Salmonella Mississippi than for Salmonella Typhimurium. Australia and New Zealand isolates sat in distinct clades for both serovars; the median single-nucleotide polymorphism distance for DT160 was 29 (range 8-66) and for Salmonella Mississippi, 619 (range 565-737). Phylogenomic data identified plausible sources of human infection from wildlife and environmental reservoirs and provided evidence supporting New Zealand-acquired DT160 in a group of travelers returning to Australia. Wider use of real-time whole-genome sequencing in new locations and for other serovars may identify sources and routes of transmission, thereby aiding prevention and control.

Wildlife diseases in New Zealand: recent findings and future challenges

Our knowledge of diseases in New Zealand wildlife has expanded rapidly in the last two decades. Much of this is due to a greater awareness of disease as a cause of mortality in some of our highly threatened species or as a limiting factor to the successful captive rearing of intensely managed species such as hihi (Notiomystis cincta), kiwi (Apteryx spp.) and kakapo (Strigops habroptilus). An important factor contributing to the increase of our knowledge has been the development of new diagnostic techniques in the fields of molecular biology and immunohistochemistry, particularly for the diagnosis and epidemiology of viral and protozoan diseases. Although New Zealand remains free of serious exotic viruses there has been much work on understanding the taxonomy and epidemiology of local strains of avipox virus and circoviruses. Bacterial diseases such as salmonellosis, erysipelas and tuberculosis have also been closely investigated in wildlife and opportunist mycotic infections such as aspergillosis remain a major problem in many species. Nutritional diseases such as hyperplastic goitre due to iodine deficiency and metabolic bone disease due to Ca:P imbalance have made significant impacts on some captive reared birds, while lead poisoning is a problem in some localities. The increasing use of wildlife translocations to avoid the extinction of threatened species has highlighted the need for improved methods to assess the disease risks inherent in these operations and other intensive conservation management strategies such as creching young animals. We have also become more aware of the likelihood of inbreeding suppression as populations of many species decrease or pass through a genetic bottleneck. Climate change and habitat loss, however, remain the greatest threats to biodiversity and wildlife health worldwide. Temperature changes will affect our wildlife habitats, alter the distribution of disease vectors and wildlife predators, or directly harm threatened species in vulnerable localities.