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.