Macroparasites (helminths and arthropods)

Helminths and parasitic arthropods are generally consid­ered to present a lower risk of invasion, epidemic spread and persistence in CTs (Rideout et al. 2017), but nonethe­less have the potential to affect both individuals and populations.

Increasingly, the conservation and biodiversity value of co-dependent parasite communities are being recognised, so treatment that aims to eliminate these parasites should be discouraged (Moir et al. 2012; Wait et al. 2017; Steven- ton et al. 2022). Additionally, the consequences of treating macroparasites are often unknown, with the potential for disruption of parasite interactions leading to increased pathogenicity of other micro- and macroparasites, reduced host immunocompetence and adverse effects on host adaption and evolution (Northover et al. 2018).

Non-native macroparasites acquired while in managed care or present in free-ranging populations warrant con­sideration for elimination. The lack of species-specific treatments for most individual macroparasite species complicates the process, with the potential for impacts on the broader co-dependent parasite community and host. However, Echinococcus granulosus, an introduced parasite that has the potential to cause significant disease in free- ranging endangered macropods such as the bridled nail­tailed wallaby (Onychogalea frenata) and brush-tailed wallabies and Proserpine rock-wallabies (P. persephone) is one macroparasite for which a potential management option exists.

For species entering managed care-breeding programs, antiparasitic treatments should be limited to macropara­sites with known pathogenic effects, be based on the results of macroparasite monitoring programs, seek to control rather than eliminate the macroparasite and be limited to situations where the macroparasite cannot be practically managed by husbandry changes (decreased stocking density, enclosure hygiene, resting enclosures where possible). Elimination of co-dependent macropara­sites from a host in managed care may lower immunity, placing individuals at risk following release to the wild and re-exposure to these parasites.

Although parasites may rapidly increase in numbers in managed care because of factors that impair host immune function, such as high stocking densities and anthropogenic stressors, recent work in brush-tailed rock-wallabies has shown that managed care may, in fact, confer advantages to the host. Comparisons of parasite prevalence, intensity of infection and comparative struc­ture of strongylid assemblages revealed significant differ­ences between managed care and free-ranging brush-tailed rock-wallaby populations, with lower para­site prevalence and intensity of infection observed in the managed care populations (Lott et al. 2012).

Parasite assemblages have been demonstrated to change following CT in eastern bettongs reintroduced from Tas. to the ACT. Longitudinal health surveillance revealed changing ectoparasite assemblages with 5 of 13 species identified at translocation failing to persist and an additional 4 species, presumably acquired from sympatric species, identified post-reintroduction (Portas et al.

The effects of parasite treatment on host-parasite dynamics in native mammals are largely unknown, although this question has recently been investigated. In a reintroduction of burrowing bettongs (B. lesueur) sourced from two separate locations and golden bandi­coots (Isoodon auratus) sourced from a single location in WA, reintroduced animals were randomly assigned to two groups receiving either no antiparasitic treatment or monthly treatment with selamectin (6 mg/kg topi­cally) for 6 mo post-reintroduction (Dunlop 2015). There was no influence of treatment group on parasite prevalence or post-release survival. However, four of seven ectoparasite species present initially failed to per­sist post-reintroduction. In that study, ectoparasites were targeted for treatment as potential vectors of Tryp­anosoma spp., which have been implicated (although causality has not been demonstrated) in brush-tailed bettong population declines (see Chapter 24). Burrow­ing bettongs sourced from one location were infected with both Trypanosoma copemani and T. vegrandis, while bettongs from the second location were infected with T. copemani only. Within 6 mo T. vegrandis was detected in previously uninfected bettongs, demonstrat­ing failure of ectoparasite treatment to prevent trans­mission post-reintroduction.

An experimental evaluation of ivermectin treatment (0.2 mg/kg SC) in reintroduced brush-tailed bettongs produced a temporary reduction of Strongyloides-like egg counts, but had no effect on other target or non-tar- get GI parasites (Northover et al. 2017). Additionally, there was no effect of treatment on body condition and parasite abundance appeared to be influenced by host population density. Further work is required to better elucidate the effects and consequences of antiparasitic therapy in native mammal translocations and until evi­dence suggests otherwise, routine antiparasitic treatment is not recommended.

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