DNA metabarcoding analysis of the bare-nosed wombat (Vombatus ursinus) diet

Wombats are native herbivorous grazers that have adapted to Australia's low-quality forage. Studies on diet selection by bare-nosed wombats (Vombatus ursinus) are limited and are either observational or based on microhistological studies. The current study determined the diet of wombats through DNA metabarcoding across five study sites in New South Wales over a one-year period. Metabarcoding was chosen as it is non-invasive, less time consuming and more specific than traditional techniques. The list of 209 plant species identified as eaten by wombats in this study is much higher than previously reported, with grasses being the most common plant group identified in all samples. Most dietary items identified were introduced plant species. Seasonal differences in plants eaten occurred at four of the five study sites and may reflect dietary abundance and floristic composition at different times of year. Further studies are required to determine if the dietary items differ markedly across the entire range of wombats, and if nutrition influences dietary preferences.

Spatial and temporal patterns of sarcoptic mange in wombats using the citizen science tool, WomSAT

There is currently limited information regarding the levels of infection and distribution of sarcoptic mange in the wombat population throughout Australia. We analyzed cases of sarcoptic mange in bare-nosed wombats reported into WomSAT, a website and mobile phone application where citizen scientists can upload sightings of wombats, burrows, and sarcoptic mange status. We used Maxent software to predict locations and the environmental factors associated with sarcoptic mange occurrence in bare-nosed wombats. A total of 1379 sarcoptic mange-infected and 3043 non-sarcoptic mange-infected wombats were reported by 674 and 841 citizen scientists, respectively. Of all the wombats reported to WomSAT from 2015 to 2019, 31.2% were infected with sarcoptic mange. Sarcoptic mange in bare-nosed wombats was reported in 502 suburbs across four states. New South Wales had the highest number of sarcoptic mange cases reported to WomSAT. There was no statistically significant seasonal variation of sarcoptic mange levels in bare-nosed wombats. The model showed that Euclidean distance to urban areas was the highest contributing factor for sarcoptic mange occurrence. As distance to urban areas decreased, the suitability for sarcoptic mange increased. Annual precipitation was the next contributing factor in the model, with higher rainfall of 400-700 mm correlating to an increase in sarcoptic mange occurrence. As the data collected to date have provided the largest-scale contemporary distribution of sarcoptic mange in wombats, data should continue to be collected by citizen scientists as it is an easy and low-cost method of collecting data over large areas. We suggest targeting the identified hotspot areas and more site-specific studies for studying and mitigating sarcoptic mange in bare-nosed wombats.

Abundance and population growth estimates for bare-nosed wombats

Wildlife managers often rely on population estimates, but estimates can be challenging to obtain for geographically widespread species. Spotlight surveys provide abundance data for many species and, when conducted over wide spatial scales, have potential to provide population estimates of geographically widespread species. The bare-nosed wombat (Vombatus ursinus) has a broad geographical range and is subject to spotlight surveys. We used 19 years (2002-2020) of annual spotlight surveys to provide the first estimates of population abundance for two of the three extant bare-nosed wombat subspecies: V. u. ursinus on Flinders Island; and V. u. tasmaniensis on the Tasmanian mainland. Using distance sampling methods, we estimated annual rates of change and 2020 population sizes for both subspecies. Tasmanian mainland surveys included habitat data, which allowed us to also look for evidence of habitat associations for V. u. tasmaniensis. The average wombat density estimate was higher on Flinders Island (0.42 ha-1, 95% CI = 0.25-0.79) than on the Tasmanian mainland (0.11 ha-1, CI = 0.07-0.19) and both wombat subspecies increased over the 19-year survey period with an estimated annual growth rate of 2.90% (CI = -1.7 to 7.3) on Flinders Island and 1.20% (CI = -1.1 to 2.9) on mainland Tasmania. Habitat associations for V. u. tasmaniensis were weak, possibly owing to survey design; however, we detected regional variation in density for this subspecies. We estimated the population size of V. u. ursinus to be 71,826 (CI = 43,913-136,761) on Flinders Island, which when combined with a previously published estimate of 2599 (CI = 2254-2858) from Maria Island, where the subspecies was introduced, provides a total population estimate. We also estimated 840,665 (CI = 531,104-1,201,547) V. u. tasmaniensis on mainland Tasmania. These estimates may be conservative, owing to individual heterogeneity in when wombats emerge from burrows. Although these two subspecies are not currently threatened, our population estimates provide an important reference when assessing their population status in the future, and demonstrate how spotlight surveys can be valuable to inform management of geographically widespread species.

Host, environment, and anthropogenic factors drive landscape dynamics of an environmentally transmitted pathogen: Sarcoptic mange in the bare-nosed wombat

Understanding the spatial dynamics and drivers of wildlife pathogens is constrained by sampling logistics, with implications for advancing the field of landscape epidemiology and targeted allocation of management resources. However, visually apparent wildlife diseases, when combined with remote-surveillance and distribution modelling technologies, present an opportunity to overcome this landscape-scale problem. Here, we investigated dynamics and drivers of landscape-scale wildlife disease, using clinical signs of sarcoptic mange (caused by Sarcoptes scabiei) in its bare-nosed wombat (BNW; Vombatus ursinus) host. We used 53,089 camera-trap observations from over 3261 locations across the 68,401 km2 area of Tasmania, Australia, combined with landscape data and ensemble species distribution modelling (SDM). We investigated: (1) landscape variables predicted to drive habitat suitability of the host; (2) host and landscape variables associated with clinical signs of disease in the host; and (3) predicted locations and environmental conditions at greatest risk of disease occurrence, including some Bass Strait islands where BNW translocations are proposed. We showed that the Tasmanian landscape, and ecosystems therein, are nearly ubiquitously suited to BNWs. Only high mean annual precipitation reduced habitat suitability for the host. In contrast, clinical signs of sarcoptic mange disease in BNWs were widespread, but heterogeneously distributed across the landscape. Mange (which is environmentally transmitted in BNWs) was most likely to be observed in areas of increased host habitat suitability, lower annual precipitation, near sources of freshwater and where topographic roughness was minimal (e.g. human modified landscapes, such as farmland and intensive land-use areas, shrub and grass lands). Thus, a confluence of host, environmental and anthropogenic variables appear to influence the risk of environmental transmission of S. scabiei. We identified that the Bass Strait Islands are highly suitable for BNWs and predicted a mix of high and low suitability for the pathogen. This study is the largest spatial assessment of sarcoptic mange in any host species, and advances understanding of the landscape epidemiology of environmentally transmitted S. scabiei. This research illustrates how host-pathogen co-suitability can be useful for allocating management resources in the landscape.

Density independent decline from an environmentally transmitted parasite

Invasive environmentally transmitted parasites have the potential to cause declines in host populations independent of host density, but this is rarely characterized in naturally occurring populations. We investigated (1) epidemiological features of a declining bare-nosed wombat (Vombatus ursinus) population in central Tasmania owing to a sarcoptic mange (agent Sarcoptes scabiei) outbreak, and (2) reviewed all longitudinal wombat-mange studies to improve our understanding of when host population declines may occur. Over a 7-year period, the wombat population declined 80% (95% CI 77-86%) and experienced a 55% range contraction. The average apparent prevalence of mange was high 27% (95% CI 21-34), increased slightly over our study period, and the population decline continued unabated, independent of declining host abundance. Combined with other longitudinal studies, our research indicated wombat populations may be at risk of decline when apparent prevalence exceeds 25%. This empirical study supports the capacity of environmentally transmitted parasites to cause density independent host population declines and suggests prevalence limits may be an indicator of impending decline-causing epizootics in bare-nosed wombats. This research is the first to test effects of density in mange epizootics where transmission is environmental and may provide a guide for when apparent prevalence indicates a local conservation threat.

Pharmacokinetic and pharmacodynamic considerations for treating sarcoptic mange with cross-relevance to Australian wildlife

Sarcoptes scabiei is the microscopic burrowing mite responsible for sarcoptic mange, which is reported in approximately 150 mammalian species. In Australia, sarcoptic mange affects a number of native and introduced wildlife species, is particularly severe in bare-nosed wombats (Vombatus ursinus) and an emerging issue in koala and quenda. There are a variety of acaricides available for the treatment of sarcoptic mange which are generally effective in eliminating mites from humans and animals in captivity. In wild populations, effective treatment is challenging, and concerns exist regarding safety, efficacy and the potential emergence of acaricide resistance. There are risks where acaricides are used intensively or inadequately, which could adversely affect treatment success rates as well as animal welfare. While reviews on epidemiology, treatment strategies, and pathogenesis of sarcoptic mange in wildlife are available, there is currently no review evaluating the use of specific acaricides in the context of their pharmacokinetic and pharmacodynamic properties, and subsequent likelihood of emerging drug resistance, particularly for Australian wildlife. This review critically evaluates acaricides that have been utilised to treat sarcoptic mange in wildlife, including dosage forms and routes, pharmacokinetics, mode of action and efficacy. We also highlight the reports of resistance of S. scabiei to acaricides, including clinical and in vitro observations.

Fine-Scale Landscape Epidemiology: Sarcoptic Mange in Bare-Nosed Wombats (Vombatus ursinus)

Landscape epidemiology provides a valuable framework to interpret, predict, and manage spatiotemporal patterns of disease. Yet, owing to the difficulty of detecting pathogen occurrence in free-ranging wildlife, disentangling the factors driving disease dynamics remains a considerable challenge, particularly at fine spatial scales. Here, we investigated the fine-scale landscape epidemiology of sarcoptic mange—a visually apparent disease caused by the mite Sarcoptes scabiei—in bare-nosed wombats (Vombatus ursinus), by: (1) characterizing the distribution and density of wombats within the landscape and (2) examining the effect of environmental variation on the occurrence and apparent prevalence of mange. Wombats were heterogeneously distributed over 19.4 km of transect space (0.096–1.39 wombats ha−1) and seven months of time (increasing by a factor of 1.76). Wombat density was negatively associated with distance to vegetation cover, supporting a general propensity for wombats to occur and burrow near vegetation (native and exotic, excluding pasture). The apparent prevalence of mange varied spatially (3.1–37.5%), with the probability of disease greater in wombats with minimal vegetation and low-lying pans in their estimated home range. We observed trends of increased prevalence in areas with more burrows available per wombat and in individuals occurring near vegetation cover (although not within their home range). Wombat density and active burrow density did not influence the prevalence of mange. This research emphasizes the fine scale at which spatiotemporal patterns of disease can manifest and is the first to investigate the influence of host density for any species with indirect transmission of S. scabiei. Collectively, our results suggest that individuals inhabiting less optimal habitat (pasture) may be at greater risk of disease, or that diseased wombats may be competitively excluded from more optimal habitat (vegetated areas). We discuss implications for understanding and managing mange in wombats and cross-applicability to other mange-affected species with environmental transmission.

Pathophysiological and Pharmaceutical Considerations for Enhancing the Control of Sarcoptes scabiei in Wombats Through Improved Transdermal Drug Delivery

Sarcoptic scabiei is an invasive parasitic mite that negatively impacts wombats, causing sarcoptic mange disease, characterized by alopecia, intense pruritus, hyperkeratosis, and eventual mortality. Evidence suggests that wombats may be unable to recovery from infection without the assistance of treatments. Transdermal drug delivery is considered the most ideal route of administration for in situ treatment in free-ranging wombats, as it is non-invasive and avoids the need to capture affected individuals. Although there are effective antiparasitic drugs available, an essential challenge is adequate administration of drugs and sufficient drug retention and absorption when delivered. This review will describe the implications of sarcoptic mange on the physiology of wombats as well as discuss the most widely used antiparasitic drugs to treat S. scabiei (ivermectin, moxidectin, and fluralaner). The prospects for improved absorption of these drugs will be addressed in the context of pathophysiological and pharmaceutical considerations influencing transdermal drug delivery in wombats with sarcoptic mange.