Fiona Knox

Little is known about the baseline health status of Australia’s native rodents. The resultant knowledge gaps are problematic for wildlife translocations, as assessing disease risk is integral to translocation planning and outcomes. A disease risk analysis was conducted for the conservation translocation of native rodents to Dirk Hartog Island, Western Australia. This analysis resulted in a recommendation for a multidisciplinary project to reduce knowledge gaps about the health status of Shark Bay mice (Pseudomys gouldii) and greater-stick-nest rats (Leporillus conditor). Between 2021 and 2022, 130 Shark Bay mice and 122 greater stick-nest rats were translocated to Dirk Hartog Island. Mucosal swabs, whole blood, faeces, and ectoparasites were collected from a subset of these individuals. Molecular testing for four infectious agents was performed, parasite burdens and haematological parameters were examined, and relationships between these variables, health metrics and post-translocation short-term survival were assessed. Necropsies with routine histological assessment on translocation mortalities were performed where feasible. Several indicators of non-infectious factors contributing to morbidity or mortality were found, highlighting the need to iteratively evaluate translocation strategies. There was also an apparent absence of some host-specific parasites, suggesting that active approaches to parasite conservation during translocations should be considered. Molecular evidence of herpesviruses, a paramyxovirus, Bartonella sp., Trypanosoma sp. and Mycoplasma spp. were detected among the translocated animals. Although not associated with morbidity or short-term mortality in this study, the disease potential of these agents is still present. Overall, these results contribute important new data on health baselines for both species, which will assist in informing future conservation planning.

Context: Chlamydia species impose major global burdens on both human and animal health. However, chlamydial infections of wild rodents have been understudied, posing limitations on assessments of disease risks for rodent conservation translocations. This is particularly true when there is evidence of infection in proposed source populations, as occurred for the Shark Bay mouse (Pseudomys gouldii) translocations to Dirk Hartog Island. Aims: The aim of this study was to reduce uncertainty surrounding the risks posed by Chlamydia for these translocations by: (1) determining the presence, prevalence and diversity of Chlamydia in rodent populations in the Shark Bay region of Western Australia; (2) identifying associations with health parameters; and (3) assessing for evidence of cross-species transmission. Methods: Swab, faecal and tissue samples from 110 wild-caught individuals (comprising five rodent and two marsupial species) were collected across four islands in Western Australia. These samples were analysed by a Chlamydiaceae 23s rRNA qPCR in a 14-month cross-sectional study conducted between 2020 and 2021. Key results: In total, 20% of all individuals (22/110; 95%CI 13.6–28.4) from five species, including 19% (19/100; 95% CI 12.5–27.8) of rodents, were positive by the Chlamydiaceae qPCR, although in low loads. Further attempts at species identification of the Chlamydiaceae were unsuccessful. Our results found no detectable adverse health associations, or significant associated pathological findings, with low molecular loads supporting an asymptomatic infection state. Additionally, there were no disease associations in Shark Bay bandicoots (Perameles bougainville) despite the presence of an ocular disease syndrome previously linked to chlamydial infection in this species. Conclusions and implications: Our findings suggest that sub-clinical chlamydial infections in wild Australian rodents may be widespread, but for the Dirk Hartog Island translocations, the risks of Chlamydia associated with movement of Shark Bay mice are likely low. The results highlight how current knowledge gaps pertaining to wildlife health can be addressed through collaborative approaches to translocation planning and implementation.

Conservation translocations have become increasingly popular for ‘rewilding’ areas that have lost their native fauna. These multispecies translocations are complex and need to consider the requirements of each individual species as well as the influence of likely interactions among them. The Dirk Hartog Island National Park Ecological Restoration Project, Return to 1616, aspires to restore ecological function to Western Australia’s largest island. Since 2012, pest animals have been eradicated, and conservation translocations of seven fauna species have been undertaken, with a further six planned. Here, we present a synthesis of the innovative approaches undertaken in restoring the former faunal assemblage of Dirk Hartog Island and the key learnings gathered as the project has progressed.