Microparasites (viruses, bacteria, fungi, protozoa)
Microparasites are generally considered to have greater potential for negative effects in CTs because of their ability to adapt/mutate and switch hosts as a result of greater virulence, short generation times and more rapid evolution (Rideout et al.
2017). As a result, they are often accorded higher priority during DRAs. However, decision making around disease screening for and management of microparasites in CTs can be challenging. For example, many host-adapted herpesviruses occur in marsupials without causing significant clinical disease (Stalder et al. 2015) (see Chapter 23). Despite reported outbreaks in managed care and the risk of disease recrudescence associated with the stressors of CT and the potential for spillover into conspecifics or sympatric species at the release site, these viruses are widespread in many populations, making exclusion of infected animals potentiallyunnecessary. Additionally, these viruses likely represent a low risk of causing significant morbidity and mortality in free-ranging populations. Conversely, pathogens such as Chlamydia pecorum in koalas (Phascolarctos cinereus) have the potential to affect the health of translocated individuals as well as any koala population present at the release site if the organism or a specific genotype is not already present. Similarly, Chlamydia-associated conjunctivitis was recognised as a potential impediment to the successful CT of western barred bandicoots (Warren et al. 2005). Treatment of disease before release in these cases represents an important component of a disease risk mitigation strategy.
Development and/or evaluation of vaccines for diseases that impact native mammals remain limited. Nonetheless, there are several vaccines that have either been evaluated or are in development that have the potential
for application to CTs. Chlamydia pecorum is a significant disease of koalas for which a prototype therapeutic vaccine has been developed (Waugh et al.
2016c). Vaccination of infected but asymptomatic or non-infected koalas before translocation would limit shedding of the organism and minimise disease risk in translocated and recipient populations. The requirement for using molecular screening methods for Chlamydia at donor and recipient sites and the need for risk mitigation strategies to avoid the introduction of non-enzootic genotypes and transmission between koalas and domestic animals before incorporating vaccination into koala CTs have been highlighted (Waugh et al. 2016b). Preliminary investigations into an anti-koala retrovirus recombinant protein-based vaccine have demonstrated the safety of the vaccine and provided evidence for an immune response in some animals, suggesting development of a protective vaccine is possible (Waugh et al. 2016a). The development of such a vaccine has obvious implications for health management in koala CTs.An inactivated encephalomyocarditis virus vaccine produced neutralising antibodies in the common wallaroo (Osphranter robustus), suggesting this vaccine might be useful in macropods, at least in CTs where this disease was considered a risk factor (McLelland et al. 2005). There is also anecdotal evidence to support the efficacy of multivalent clostridial vaccines in macropods and a Bor- detella bronchiseptica vaccine in various macropod species and koalas that could have applications for disease management in ex situ-breeding programs for CTs and pre-release treatment (Blanshard and Bodley 2008; Vogelnest and Portas 2008).
5.2