DISEASE RISK ANALYSIS

Given the potential effects of disease on translocated ani­mals and recipient populations, formal methods have been developed to assess and mitigate disease risk (i.e. DRA). Ideally, the DRA involves a multidisciplinary team undertaking risk analysis to identify hazards that may enter a specified animal population, the likelihood of such introductions occurring, their consequences and the measures that may be applied to mitigate either the likeli­hood of introduction or the magnitude of consequences (Jakob-Hoff et al.

2.1 Qualitative approach to DRA

Qualitative DRA is most commonly used in wildlife pro­grams. Qualitative analyses indicate the likelihood of an outcome, expressed as high, medium, low or negligible, whereas quantitative analyses express an outcome numerically. Jakob-Hoff et al. (2014a) describes several quantitative DRA approaches that will not be discussed here. Meaningful quantitative analysis requires detailed epidemiological data, often missing for disease risk sce­narios involving wildlife (e.g. health surveillance data, prevalence of disease in populations, ecological data on population size and density, and validated diagnostic tests) (Sleeman et al. 2012). Qualitative analysis can be complemented by some quantitative analysis where suit­able data is available.

2.2 Sources of information

In 2014 the International Union for the Conservation of Nature (IUCN) and World Organisation for Animal Health (OIE) jointly published the IUCN Manual of Procedures for Wildlife Disease Risk Analysis (‘the Manual’) (Jakob-Hoff et al.

A fundamental limitation in wildlife DRA is lack of robust data and information. Knowledge of the identity, distribution, prevalence and pathogenicity of parasites of free-ranging wildlife is limited. Host-parasite interac­tions are complex and affected by broader ecosystem processes (Sainsbury and Vaughan-Higgins 2012) and species information is often extrapolated from phyloge- netically related or physiologically similar species. How­ever, these assumptions should be explicitly acknowledged as they may not be correct.

Determination of potential parasite hazards for a given species is complex, particularly when pathogenic­ity and immune response varies with host susceptibility (Rideout et al. 2017). Studies focusing on emerging infectious disease have suggested there are common characteristics of parasites that increase the risk of inva­sion, epidemic spread and persistence. Generally, greater concern should be given to ‘microparasites’ compared with ‘macroparasites’, because of the greater likelihood of host switching and adaptation given shorter genera­tion times and rapid evolution (Tompkins et al.

Disease surveillance of free-ranging wildlife in Aus­tralia primarily targets species of interest either for con­servation purposes or investigation of disease outbreaks (Pacioni et al. 2015; Reiss et al. 2015). However, broad surveillance is also being coordinated by Wildlife Health Australia (see Chapter 1), which collates and manages national wildlife surveillance data collected by zoos, selected private veterinary practices and universities (Cox-Witton et al. 2014). These resources, together with published and unpublished literature, techniques for elic­iting expert opinion and consultation with relevant experts and stakeholders, comprise a rich source of infor­mation to inform or update a DRA.

2.3 Methodology

Although there are multiple published methods of DRA, the majority of authors follow a basic approach in a logical stepwise manner (Fig. 3.1). This chapter primarily focuses on the IUCN method (Jakob-Hoff et al. 2014a) and the Institute of Zoology (IoZ) method, which incorporate the Sainsbury and Vaughan-Higgins (2012) and the Masters and Sainsbury (2011) methods. The IUCN guidelines are currently under revision and once published should be consulted as a primary resource for DRA.

2.3.1 Problem description

Questions: ‘What is the specific question for this DRA?’ and ‘What kind of risk analysis is needed?’

Method: Outlines the background and context of the problem;

• The DRA Question is formulated in consideration of the problem the DRA is being undertaken to address.

• Identify the goal, scope and focus of the DRA

• Goal - to identify and assess the likelihood of the hazard(s) being introduced and spreading or becoming established (in the area of translocation), together with the likelihood of and the likely magni­tude of the potential consequences for wild animal, domestic animal or human health as a result of the activity and to recommend risk mitigation measures if appropriate (Jakob-Hoff et al. 2014a).

• Scope - will consider where the boundaries of the DRA lie (e.g. the species, populations and geo­graphic areas of interest, time-frame). It could also define the limitations under which the DRA is con­ducted, such as availability of sources of informa­tion (including expertise and stakeholder input).

• Focus - narrows the scope to determine the specific purpose of the DRA, for example, ‘The focus of this DRA is to identify, assess and evaluate mitigation options for the potential health impacts associated with the acquisition and zoo or sanctuary manage­ment of species X transferred from location 1 to location 2’.

• State assumptions and limitations and specify accept­able level of risk.

• In many cases a site visit to the potential capture, breeding (if appropriate) and release sites will be required to assess the risks.

2.3.2 Risk communication (applies at every DRA step)

Questions: ‘Who are the key stakeholders?’, ‘Who has an interest?’, ‘Who has knowledge or expertise to contrib­ute?’ and ‘Who can influence the implementation of rec­ommendations arising from the DRA?’

Method:

• Involves continuous communication between stakeholders.

• Engagement with relevant experts and stakeholders to maximise the quality of analysis and the probability that the recommendations arising from the DRA will be implemented.

• Will determine stakeholders’ acceptable level of risk for the translocation.

2.3.3 Hazard identification

Questions: ‘What can cause disease in the population of concern?’, ‘How can this happen?’ and ‘What are the potential consequences?’

Method:

• Identify all possible hazards of concern and categorise as ‘infectious’ and ‘non-infectious’.

• Establish criteria for ranking the importance of each hazard within the bounds of the goal.

• Consider potential direct and indirect consequences of hazards to help decide which should be subjected to full risk assessment (e.g. consequences to/for: health [animal and human], welfare, environmental and eco­logical, social and psychological, economic, political, national security [e.g. notifiable diseases]).

Table 3.1. Categorisation of hazards according to point on the translocation pathway at which the host-parasite interaction occurred, according to the Institute of Zoology method (adapted from Masters and Sainsbury 2011; Sainsbury and Vaughan-Higgins 2012)

• Exclude hazards with zero or negligible probability of release or exposure.

• Consider construction of graphical models (e.g. a scenario tree for high priority hazards of concern), to facilitate identification of the various biological pathways leading to exposure of the susceptible animals or people to the hazard, as well as, potential ‘outbreak’ scenarios (Jakob-Hoff et al. 2014a).

In addition to the above, the IoZ method identifies hazards that may introduce disease through different origins (e.g. whether or not the hazard is novel to a host, whether it is affected by immune interactions between host and parasite and the presence of ecological or geo­graphical barriers) (Table 3.1).

2.3.4 Translocation pathway

The translocation pathway is unique to the IoZ method and illustrates the points at which different hazards can trigger disease (Fig. 3.2). It is a useful way to conceptual­ise and identify hazards throughout the translocation

Fig. 3.2. Translocation pathway (black arrows) for introduction of eastern barred bandicoots (Perameles gunnii) to Phillip Is. and French Is., Vic., Australia. White arrows refer to points in the translocation pathway at which different hazards may trigger disease (adapted from Jakob-Hoff et al. 2016).

process. It also identifies barriers to parasite transmis­sion. For example, geographical barriers are natural environmental barriers preventing movement between populations (e.g. bodies of water, mountain ranges), while ecological barriers could include physical, behavioural and reproductive behaviours preventing interactions between populations, representing an ecological niche (Masters and Sainsbury 2011; Bobadilla Suarez et al. 2017). However, for many species, owing to data defi­ciency, the presence of an ecological barrier may not always be apparent. If either geographical or ecological barriers are crossed, source and destination hazards need to be considered and the likelihood of exposure to novel parasites increases. This is important as evidence sug­gests that major epidemics associated with translocations have arisen from source hazards (Walker et al. 2008;

Sainsbury and Vaughan-Higgins 2012). However, if source and destination environments are not separated by barriers, overall risk from disease is reduced (Boba­dilla Suarez et al. 2017) and the DRA process will likely be simpler.

2.3.5 Risk assessment

Question: ‘What is the likelihood and consequences of a specified hazard occurring within an identified pathway or event?’

Method:

• For each hazard of concern construct a scenario tree that graphically depicts the exposure and transmis­sion pathways to and between the target (translocation and destination) populations.

• Entry assessment - an estimate of the likelihood of the translocated animals introducing the hazard into an area.

• Exposure assessment - an estimate of the likeli­hood of susceptible animals being exposed to the hazard, becoming infected (parasite hazards) and disseminating the hazard at the release site.

• Consequence assessment - an estimate of the likely magnitude of potential biological, environ­mental and economic consequences associated with the entry, establishment or spread of the hazard and the likelihood of their occurrence. Includes conse­quences for the individuals moved, populations of same and other species and for the wider ecosystem at the destination.

• Risk estimation - summarises the entry, exposure and consequence assessments to provide an overall measure of risk.

2.3.5 Risk management

Questions: ‘What can be done to minimise the likelihood of a hazardous event?’ and ‘What can be done to mini­mise the consequences once a hazardous event has happened?’

Method:

• Identify and evaluate management options that can be implemented to minimise identified risks (e.g. pre­release quarantine, screening for parasite hazards, minimising stress (low stocking densities), hygiene (cleaning and disinfection), prophylactic or other med­ications, environmental treatments, vector control).

• Option evaluation - expert consideration of options for feasibility and effectiveness. Ideally, options should be feasible and highly effective.

2.3.6 Implementation, monitoring and review

Questions: ‘How will the selected risk management options be implemented?’ and once implemented, ‘Are the risk management actions having the desired effect?’ and if not, ‘How can they be improved?’

Method:

• Formulate the action and contingency plans and establish a process and timeline for the monitoring, evaluation and review of risk management actions.

• Detail plans of actions to be taken, why, when and by who, and the associated resources (time, money, people, equipment).

• Monitor risk management measures to ensure that they are achieving the intended results.

• Develop processes to evaluate the effectiveness and prac­ticality of risk management options - ideally annually.

• The review may result in a clearer understanding of the problem and enable refinement of the DRA.

2.4 Transparency and time for completion

Given the limitations and assumptions made in wildlife DRA, evidence to support decisions on estimation of dis­ease risk is important (Dalziel et al. 2017). It is recom­mended that referencing and recording to highlight uncertainty and subjectivity should be undertaken in the form of an accessible and transparent final written report. In the majority of DRA, stakeholders will identify multi­ple hazards. A robust option is to prioritise hazards for initial risk assessment based on the opinion of a panel of experts (Jakob-Hoff et al. 2016).

Time for completion of a DRA is a critical considera­tion. Completion of a DRA using the IoZ and IUCN methods can be time-consuming, especially when an exhaustive hazard list has been created. However, addi­tional methodologies can provide a preliminary assess­ment of the need for a full pre-translocation risk analysis (e.g. the DRA-T) (McInnes et al. 2011). A suggested mini­mum time-frame for a comprehensive DRA following the IUCN and IoZ methodology is 6 mo, allowing time for planning the DRA, initial desktop review of available lit­erature, consultation with relevant experts and stake­holders, analysis of results and preparation and review of a final report. Ideally, the DRA should be completed a minimum of 1 yr ahead of the planned translocation. This is advocated because implementation of DRA rec­ommendations ahead of the translocation may require considerable time. It may include further disease testing of animals at the source and/or destination to enable either quantification of risk or detection of hazards, implementation of biosecurity measures, construction of facilities, preventive medicine protocols, briefing and training of staff and application for permits from relevant government compliance bodies.

In some cases, neither time nor financial resources are available for such a protracted process, so a cost-benefit assessment should be made for each approach. This would include the urgency of the translocation, the level of perceived risk to the focal species and/or populations and the availability of expertise and other resources (R Jakob-Hoff pers. comm.).

It is highly recommended that an initial and ongoing budget that factors in post-release health, disease and population monitoring to enable critical analysis of the translocation outcome is included. This will also inform annual updating of disease risk management protocols and, ultimately, advance the DRA process.

2.5 Disease screening, disease risk management and post-release health monitoring

Disease screening of both the source and destination populations should be considered for data deficient spe­cies (see Chapter 2). Such surveys can be costly, are often logistically difficult and time-consuming and still do not guarantee detection of all parasites present. However, efficient use of available resources can be improved if disease screening is targeted to hazards assessed to have medium to high consequences to translocation success. If finance limits screening, it is recommended that baseline samples, as a minimum (e.g. blood, serum, faeces), be col­lected and stored to allow retrospective analysis should a disease event occur.

Biosecurity measures such as isolation (quarantine) and the use of barrier principals to reduce the likelihood of transmission of parasites to and from the target species are useful disease risk management strategies (see Chapter 2). The isolation period also provides opportunity for obser­vation, expression of disease in infected individuals, dis­ease screening and treatment (OIE 2010; Vaughan-Higgins et al. 2017). Vaughan-Higgins et al. (2017) presented evi­dence to support the value of biosecurity in preventing the transfer of infectious agents between populations in wild­life translocations and recommended that biosecurity pro­tocols always be implemented. Disease outbreaks have occurred in association with previously unknown parasites that a DRA could not have identified but adequate biosecu­rity measures may have prevented (e.g. chytridiomycosis) (Walker et al. 2008). However, isolation must be balanced against the stress or injury that animals held in close con­finement may experience (Dickens et al. 2010) and the financial cost involved (Ewen et al. 2012b).

Disease control may include vaccination, therapeutics, low stocking densities and minimisation of stress (see Chapter 2). One of the overarching goals of CTs is restora­tion of the ecosystem. Attempts should therefore be made to ensure native parasites, which have co-evolved with their host in their region and ecosystem, are maintained in the translocated population (Rideout et al. 2017). This may involve initial screening and investigation of ways in which commensal or potentially pathogenic parasites can be conserved through modification of therapeutic regi­mens (Sainsbury and Vaughan-Higgins 2012).

Post-release health monitoring is particularly impor­tant when health and disease data are lacking and should be incorporated into all translocations. Post-release clini­cal and pathological investigations may detect unknown or undetected hazards (which may lead to disease out­breaks at the destination), in target species and related species found sick or dead at the destination site (Sains­bury and Vaughan-Higgins 2012).

3.