CONCLUSION
A DRA is a living and evolving document that is reliant on stakeholder collaboration and communication to achieve its purpose. The high levels of uncertainty associated with scarcity of data on wildlife disease can largely be off-set by:
• using a structured, evidence-based and iterative approach
• clarifying the goal, scope and focus of the DRA from the outset
• accessing both published and unpublished information through expert and stakeholder consultation
• transparency in explicit listing of limitations and assumptions
• post-translocation monitoring to evaluate effectiveness of risk mitigating measures
• identification of research priorities to address key information gaps identified through the DRA process.
Table 3.2.
Synopsis of critical components of the DRA process for the eastern barred bandicoot (Perameles gunnii) (adapted from Jakob-Hoff et al. 2016)Problem description
• Mainland eastern barred bandicoot (EBB) (Perameles gunnii) extinct in the wild, recovery program initiated in 1989.
• Key threatening processes - habitat loss and fox predation.1
• Predator-barrier fences erected at three sites in Vic. to protect extant populations.
• Phillip Is. and French Is. identified as areas with suitable habitat for introduction but are outside this species' historic range.2
• Both islands inhabited by people, livestock, pets and wildlife species.
• Fox and feral cat control effective but ongoing.
• Toxoplasmosis is the only disease that has compromised previous EBB release.2
• Risk mitigation strategies have been developed from previous translocations.
| DRA question | 'What is the risk from disease arising from identified health hazards, as a consequence of managed care-to-wild translocations, that constitute a threat to the recovery of free-living EBB populations and how can this risk be minimised?' |
| DRAgoaI | Develop a disease risk management strategy for EBB being translocated to French Is. and Phillip Is. based on structured, evidence-based analysis of current information. |
| Scope and focus | Conduct a qualitative analysis of relevant literature on the susceptibility of EBBs to infectious or non-infectious disease on French Is. or Phillip Is. and/ or passing a disease onto existing vertebrate island fauna. Identification, assessment and mitigation of all significant health risks to EBB and existing vertebrate island fauna, associated with the translocation. |
| Assumptions | EBBs are susceptible to health hazards recorded in Peramelidae and are susceptible to pathogens demonstrated to have a broad host range in mammals. Available data combined with the analytical and decision-making processes will enable reasonable decisions to be made to minimise health risks. |
Limitations Limited understanding of the range and epidemiology of potential pathogens of EBB.
Translocation pathway Fig. 3.2
Hazard identification
• Review of literature and qualitative analysis at 2-day workshop prepared for further discussion.
• Sourceorcarrier parasite hazards reported from EBBs reviewed against likelihood Ofexposuretothe islands' resident vertebrates and the consequences of exposure. Agreed that any potential disease risk to people and domestic animals be managed to a negligible level, low to negligible for resident wildlife and low to moderate for the EBB.2
• Foreach population Ofinteresta rank of low, medium or high for each hazard in terms Oflikelihood and consequence Ofexposurewas assigned using a risk hazard prioritisation matrix.2
• Three potential medium-to-high disease risks identified: toxoplasmosis (EBBs); enteric pathogens (Salmonella, Campylobacter, Escherichia coli, Yersinia, Cryptosporidium and Giardia) (humans and domestic animals); ectoparasites (fleas, ticks, mites) (resident wildlife).
• EBB considered very Unlikelyto Significantlyadd to risk posed by Ross Rivervirus (RRV) to human population, but agreed Tiskassessmentshould be conducted on this pathogen given public concern. Given time constraints, a small working group with relevant expertise would complete the risk assessment for RRV following the workshop.
Risk assessment
• Detailed example of risk assessment of Toxoplasma gondii (Table 3.3).
• Highlighted the specific questions answered, level of detail and referencing needed to ensure transparency (Table 3.3).
• Knowledge gaps identified and measures to reduce uncertainty noted.
Risk management
• Diagram constructed to represent potential points Ofinteraction between host and hazard from the source to the destination site.
• Used as a basis for identifying Critical Control Points (CCPs)3 where risk management interventions could be made to reduce likelihood of exposure or reduce impact on the host if exposed.
• Risk mitigation options qualitatively assessed according to likely feasibility and effectiveness and an action plan for recommendations developed.2
Risk communication
• Communicated the rigour of the DRA process and key results with stakeholders, actively (e.g. through open sessions to community groups such as the Phillip Is. Nature Parks Board, EBB recovery team) or passively (e.g. through information sheets outlining processes and key results, for example to Zoos Victoria, and the broader community).
• Full detailed report also made available to interested parties and available online.
1Scarlettefa/. 1992; 2Jakob-Hoff etal. 2016; 3Jakob-Hoff etal. 2014a
- Disease risk analysis for wildlife translocations
Table 3.3. Risk assessment for the hazard Toxoplasma gondii for the introduction of eastern barred bandicoots (Perameles gunnii) to Phillip Is. and French Is., Vic., Australia (modified from Jakob-Hoff et al. 2016)
Justification of hazard
• Felids are the definitive hosts of T.
gondii.• Feral cats and T. gondii are present on French Is. and Phillip Is.
• Two eastern barred bandicoots (EBBs) (Peramelesgunnii) released onto French Is. during a trial[I] were found to have died of toxoplasmosis.2
Risk assessment
| Release assessment | Exposure assessment | Consequence assessment |
| • Cats and T. gondii | • Cats infected with T. gondii primarily by ingestion of either bradyzoites or | • EBB susceptible and previous |
| present on proposed | tachyzoites in the tissues of infected intermediate hosts or sporulated | experience of EBB deaths |
| destination islands | oocysts from other cats. | caused by T. gondii on French |
| • Release assessment for | • Most cats infected by ingestion of tissue cysts shed oocysts in faeces | Is. |
| hazard is high | within 3-10 days, may continue to shed up to 20 days.3 • Any non-felid warm-blooded vertebrate can be an intermediate host, whereby T. gondii tachyzoites can cause acute toxoplasmosis. Thereafter T. gondii persists as bradyzoites in tissue cysts. • Hosts can be infected prenatally or postnatally. Invertebrates can carry T. gondii oocysts within their gut as a result of coprophagia or ingestion of soil or plant material contaminated with cat faeces. • Postulated route of infection in insectivorous marsupials such as bandicoots is consumption of paratenic hosts, including soil-associated arthropods, insects or annelids such as earthworms.4,5 • Risk of transmission to direct hosts (canid/felid) following predation of infected EBB. • As feral cats and T. gondii are known to be present on both islands, the risk of EBB exposure to this disease hazard is assessed as high. | • If cat density low, environmental contamination with T. gondii likely to be patchy, reducing exposure likelihood and reducing infectious dose.6 • On this basis, although consequences to individual EBB can be high, the consequence to the population assessed as moderate. |
Risk evaluation
• EBBs only capable of transmitting this parasite by being eaten, risk to humans and non-carnivorous animals negligible and, given that bandicoots are likely to comprise an extremely small part of carnivore diets, the risk to them is low.
• Overall risk to the EBB populations on French Is. and Phillip Is. assessed as moderate. Based on the risk assessment above, preventative measures should be adopted to reduce the risks from T. gondii
Risk management options
• Prevention - limit exposure to oocysts: Reduce cat densities through baiting.7
• Treatment - usually unsuccessful but can be attempted (see Chapter 21).
• Control - oocysts are highly resistant and can survive up to 18 mo in the environment, but can be inactivated or destroyed.4
• Minimise stressors on EBB - pre-release health management, husbandry, housing and transport; suitable habitat at release site; food availability; season of release to ensure adequate food supply, suitable temperature/rainfall patterns.
ACKNOWLEDGEMENTS
I gratefully thank Richard Jakob-Hoff and Bethany Jackson for comments on the manuscript.