Keywords
Wildlife disease, surveillance, wild deer, parasites, Australia, 18S rRNA gene

Introduction

The frequency of emerging and re-emerging infectious diseases outbreaks in wildlife reservoirs has increased during recent decades (Gortazar, Acevedo, Ruiz-Fons, & Vicente, 2006), raising new questions about disease pathogenesis and epidemiology. The increasing role of wildlife in the emergence of livestock diseases is due to multiple changes occurring within wildlife and livestock populations, including encroachment on natural habitats, climate change and alteration of population demographics. Most notably, alteration of wildlife population demographics caused by anthropogenic landscape modification or introduction of non-native species can create new interfaces between livestock and wildlife, potentially exacerbating processes that favour pathogen transmission (Gortazar et al., 2015). Importantly, transmission of an infectious agent at the wildlife/livestock interface may occur directly through interspecies contact, or indirectly through shared space or vectors (Gortazar et al., 2006; Miller, Farnsworth, & Malmberg, 2013).
Australian livestock species are infected with multiple parasitic pathogens of economic relevance, such as Fasciola hepatica(‘liver fluke’), Echinococcus granulosus (‘hydatids’),Theileria orientalis , Babesia bigemina , Babesia bovis and Anaplasma marginale (Bock, deVos, & Molloy, 2006; Jenkins, 2018; Thompson, 2018). Further, infection with Neospora caninum has been identified as a major cause of abortion in cattle and investigations in Queensland have estimated a prevalence of around 20% (Reichel, 2000). Other pathogenic genera such as Trypanosoma ,Sarcocystis and Toxoplasma have also been detected in Australian wildlife species (Munday & Mason, 1980; Pan et al., 2012; Thompson, Godfrey, & Thompson, 2014). These pathogens share a large diversity and distribution of their intermediate hosts and are prevalent in domestic animals, thus they constitute a biosecurity concern for livestock industries (Spratt & Beveridge, 2018).
Australia’s livestock export industry was valued at approximately AU$1,780 million for the 2015–16 financial year (Australian Government Department of Agriculture, 2020b). Although Australia is currently free from some of the world’s most important livestock diseases such as foot-and-mouth disease and avian influenza H5N1, endemic infectious agents impact on livestock industries. For instance, the economic losses produced by Neospora caninum in Australian cattle were estimated at AU$85 million and AU$25 million per annum for the dairy and the beef cattle industries, respectively (Reichel, 2000). Moreover, exotic diseases constitute a major threat to Australia’s livestock industry and a severe outbreak would considerably impact Australia’s production and access to export markets (Australian Government Department of Agriculture, 2020a).
Among Australian wildlife capable of carrying pathogens transmissible to livestock, deer are of substantial concern as they commonly feed on pasture and crops in agricultural landscapes, achieve high local population densities, are highly mobile and are susceptible to a wide range of viral, bacterial and parasitic infections that may affect other ungulates (Cripps, Pacioni, Scroggie, Woolnough, & Ramsey, 2019). Deer were introduced in Australia as game animals in the mid-19th century and have successfully adapted to the climate and environmental conditions. In addition to the initial intentional releases, there are records of numerous animals establishing wild populations after escaping from deer farms (Davis et al., 2016). Currently, six non-native deer species have established viable wild populations in most Australian habitats (excluding the arid interior and north-west), and most of these species are expanding their distributions and abundances (Davis et al., 2016; Forsyth, Stamation, & Woodford, 2016).
Numerous pathogens have been detected in various deer species worldwide, including protozoan parasites with epidemiological relevance to humans and domestic animals. For example, serological evidence ofNeospora and Toxoplasma exposure has been detected in fallow (Dama dama ) and red deer (Cervus elaphus ) in Poland (Bien, Moskwa, Bogdaszewski, & Cabaj, 2012), Italy (Rocchigiani et al., 2016) and Mexico (De La Torre et al., 2017). Evidence of piroplasm infection (Babesia and Theileria ) was reported in the same two deer species in Europe and China (Garcia-Sanmartin et al., 2007; Hornok et al., 2017; Li et al., 2014; Tampieri et al., 2008; Zanet et al., 2014). Also, Plasmodium parasites have been identified in farmed North American white-tailed deer (Odocoileus virginianus ) (Guggisberg, Sayler, Wisely, & John, 2018) and South American pampas deer (Ozotoceros bezoarticus ) (Asada et al., 2018).
Limited information is available regarding the overall infection status of Australian wild deer populations. In particular, serological evidence is restricted to parasitic helminths, Leptospira and some endemic livestock viruses in red deer (Cervus elaphus ) from Queensland (McKenzie et al., 1985) and rusa deer (Rusa timorensis ) from New South Wales (Moriarty, 2004). Importantly, the prevalence of blood-borne parasites known to infect deer overseas has not been investigated in Australian wild deer populations. Therefore, the role that wild deer might play in the spread of these diseases to livestock remains unclear, and the transmission of such pathogens to livestock has yet to be demonstrated in Australia. Addressing this knowledge gap is critical to anticipating how such pathogens might be transmitted to other animals (including livestock and humans), and how these diseases may be controlled. To this end, a molecular survey of parasitic genera previously detected in Australian livestock (Theileria ,Babesia and Neospora ), and in deer and livestock overseas (Trypanosoma , Plasmodium , Sarcocystis andToxoplasma ), was performed in a wide range of deer blood samples, representing four deer species, collected during 2018 and 2019 across four Australian states and territories.