Population‐scale treatment informs solutions for control of environmentally transmitted wildlife disease

Abstract

Long‐term pathogen control or eradication in wildlife is rare and represents a major challenge in conservation. Control is particularly difficult for environmentally transmitted pathogens, including some of the most conservation‐critical wildlife diseases. We undertook a treatment programme aimed at population‐scale eradication of the environmentally transmitted Sarcoptes scabiei mite (causative agent of sarcoptic mange) during an epizootic in bare‐nosed wombats (Vombatus ursinus). Field trial results were used to parameterize a mechanistic host‐disease model that explicitly described indirect transmission, host behaviour and viable disease intervention methods. Model analysis shows that elimination of S. scabiei in the wild is most sensitive to the success of treatment delivery, and duration of the programme. In addition, we found the frequency that wombats switch burrows was an important positive driver of mite persistence. Synthesis and applications. This research emphasizes the utility of applying model‐guided management techniques in order to achieve practical solutions for controlling disease in the field. We find that control efforts of Sarcoptes scabiei are most successful when simultaneous improvements are made to the current best‐practice protocol, specifically the implementation of better treatment application methods in combination with a longer lasting treatment. These suggested management changes may also reduce the resources and field effort required to implement a successful regime. Furthermore, our approach and findings have applicability to other species affected by S. scabiei (e.g. wolves, red foxes, Spanish ibex and American black bear), as well as other conservation‐critical systems involving environmental transmission (e.g. bat white‐nose syndrome and amphibian chytridiomycosis).

Fluralaner as a novel treatment for sarcoptic mange in the bare-nosed wombat (Vombatus ursinus): safety, pharmacokinetics, efficacy and practicable use

“…Establishing the safety, pharmacokinetic profile and efficacy of chemotherapeutic agents is a crucial step in the fight against infectious diseases that threaten wild animal health, conservation and welfare [ 1 – 5 ]. Despite this, veterinary drugs are often employed in the control of diseases in wildlife populations based on knowledge extrapolated from domestic animals, rather than through prior experimentation with target species [ 6 – 8 ]. Such pharmacological inference may result in treatment failure due to inefficacy or in undesirable adverse effects due to inter-species pharmacokinetic differences [ 8 – 10 ].…”

“…Despite this, veterinary drugs are often employed in the control of diseases in wildlife populations based on knowledge extrapolated from domestic animals, rather than through prior experimentation with target species [ 6 – 8 ]. Such pharmacological inference may result in treatment failure due to inefficacy or in undesirable adverse effects due to inter-species pharmacokinetic differences [ 8 – 10 ]. Sarcoptic mange (SM) is one such disease, for which numerous treatment strategies adapted from domestic animals have been attempted in wildlife, but where consensus on an evidenced-based, safe, efficacious and feasible solution for in situ disease control remains elusive [ 10 , 11 ].…”

“…The conspicuous disease presentation [ 36 , 40 ] and well-documented impacts of localised SM epizootics [ 15 , 18 ] have engendered widespread public concern for the welfare and conservation of BNWs [ 41 ] and increased the appetite for interventions in recent years [ 10 , 41 ]. Thus, the scientific, government, wildlife rehabilitation and animal welfare communities have all participated in various chemotherapeutic disease control attempts, either at the individual level or population level [ 8 , 9 , 39 , 41 ]. To date, this has most often involved administration of the macrocytic lactones (MLs), topical moxidectin [ 8 , 38 ] or subcutaneous ivermectin [ 36 , 42 ], to diseased BNWs.…”

“…Thus, the scientific, government, wildlife rehabilitation and animal welfare communities have all participated in various chemotherapeutic disease control attempts, either at the individual level or population level [ 8 , 9 , 39 , 41 ]. To date, this has most often involved administration of the macrocytic lactones (MLs), topical moxidectin [ 8 , 38 ] or subcutaneous ivermectin [ 36 , 42 ], to diseased BNWs. However, treatment success has proved highly variable and is limited by: (i) an absence of conclusive dose-determination studies and therefore an incomplete understanding of dose rates required to effectively treat varying degrees of SM in BNWs [ 10 , 38 , 41 , 43 ]; (ii) pharmacokinetic and pharmacodynamic limitations, such as short durations of action and inefficacy against mite ova, that necessitate frequently repeated administration over several months [ 8 , 10 , 38 , 41 , 42 ]; and (iii), challenges associated with the direct delivery of drugs to wild animals, which are amplified by the need to re-treat the same individual on multiple occasions [ 8 , 10 , 38 , 41 , 43 ].…”

Comment on: “The treatment of sarcoptic mange in wildlife: a systematic review”

“…Pharmacological treatment of mange in wild animals mostly produces individual healing, but its effects on achieving control or eradication in a population are mostly inconclusive [21]. Therefore, gathering more information on the population and environmental effects and on the consequences of massive antiparasitic treatments has been recently recommended, approaching the management of sarcoptic mange in wildlife populations from a wider ecological perspective [22].…”