Prevalence of Liver Fluke in Macropods and Cervids with Inferences for Livestock Transmission and Control

Abstract

<p>Domestic livestock are highly susceptible to liver fluke (Fasciola hepatica) and suffer from the effects of fasciolosis in regions endemic to the intermediate snail host. Other definitive hosts include herbivorous wildlife such as macropods and cervids. These wildlife species are often observed grazing alongside livestock yet their potential impact on livestock production, as reservoirs of liver fluke infection, is largely unknown; including their role as vectors for anthelmintic resistance. The Northern Tablelands of NSW, Australia is a productive livestock region but is also a region where the liver fluke snail is endemic. For these reasons, this region was a suitable environment in which to investigate three main aspects of this thesis; (i) grazier perceptions and management practices for liver fluke control, (ii) liver fluke prevalence in macropods and Cervids, and (iii) cross-species transmission and vectors for anthelmintic resistance.</p> <p>A survey of graziers was used to identify management practices for liver fluke in livestock, and for identifying farm sites for testing of macropod faeces for the presence of liver fluke. Graziers relied exclusively on anthelmintics for liver fluke control with few having adopted integrated parasite management (IPM) strategies to reduce disease prevalence. Macropods (eastern grey kangaroo and common wallaroo) and cervids (fallow deer; from routine pest or herd management programs) examined on graziers’ farms were identified with active or resolved infections, with prevalence of up to 45 % in both species across “high” risk farm sites. Gross pathology of the liver, attributed to liver flukes, correlated strongly with fluke burden and revealed the inherent ability of wildlife to resolve infections. Examination of macropods also provided the opportunity to assess the commercial BIOK201-2 Monoscreen AgELISA Fasciola hepatica (Bio-X Diagnostic, Belgium) as a diagnostic tool for use in macropods. This assay was a suitable test for the detection of liver fluke in macropods however gross pathology of the liver may influence sensitivity. Sheep subsequently infected with liver flukes originating from macropods confirmed cross-species transmission. The role they played as vectors for anthelmintic resistance remains inconclusive and warrants further investigation.</p> <p>Overall, the research reported in this thesis has revealed that the low adoption of IPM practices by graziers for liver fluke in livestock could ultimately threaten future control within the region. Free-roaming wildlife cohabiting farms pose further challenges as macropods and cervids are able to harbour liver fluke and have the potential for cross-species transmission. Better adoption of IPM strategies including monitoring of wildlife for liver fluke and/or actively managing their ingress onto livestock grazing land will assist both the efficacy and sustainability of liver fluke control within this region.</p>