Draft pest risk analysis report for ‘

2 Method for pest risk analysis

A PRA is ‘the process of evaluating biological or other scientific and economic evidence to determine whether an organism is a pest, whether it should be regulated, and the strength of any phytosanitary measures to be taken against it’ (FAO 2008). A pest is ‘any species, strain or biotype of plant, animal, or pathogenic agent injurious to plants or plant products’ (FAO 2008).

Quarantine risk consists of two major components: the probability of a pest entering, establishing and spreading in Australia from imports; and the consequences should this happen. These two components are combined to give an overall estimate of the risk.

Unrestricted risk is estimated taking into account the existing commercial production practices of the exporting country and that minimal on-arrival verification procedures will apply. Restricted risk is estimated with phytosanitary measure(s) applied. A phytosanitary measure is ‘any legislation, regulation or official procedure having the purpose to prevent the introduction and/or spread of quarantine pests, or to limit the economic impact of regulated non-quarantine pests’ (FAO 2008).

A glossary of the terms used is provided at the back of this PRA report.

PRAs are conducted in three consecutive stages.

2.1 Stage 1: Initiation

For ‘Ca. L. psyllaurous’, careful consideration was given to the potential pathways for entry of the bacterium and its vector B. cockerelli into Australia.

For this PRA, the ‘PRA area’ is defined as all of Australia.

2.2 Stage 2: Pest risk assessment

The following three, consecutive steps were used in this pest risk assessment:

2.2.1 Pest categorisation

Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Method for PRA

economic importance to the area endangered thereby and not yet present there, or present but not widely distributed and being officially controlled’ (FAO 2008). The process of pest categorisation is summarised by the IPPC in the five elements outlined below:

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  identity of the pest
  
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  presence or absence in the PRA area
  
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  regulatory status
  
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  potential for establishment and spread in the PRA area
  
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  potential for economic consequences (including environmental consequences) in the PRA area.
  

2.2.2 Assessment of the probability of entry, establishment and spread

The probability of entry describes the probability that a quarantine pest will enter Australia as a result of trade in a given commodity, be distributed in a viable state in the PRA area and subsequently be transferred to a host. It is based on pathway scenarios depicting necessary steps in the sourcing of the commodity for export, its processing, transport and storage, its use in Australia and the generation and disposal of waste. In particular, the ability of the pest to survive is considered for each of these various stages.

For the purpose of considering the probability of entry, Biosecurity Australia divides this step of this stage of the PRA into two components:

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  Probability of importation: the probability that a pest will arrive in Australia when a given commodity is imported
  
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  Probability of distribution: the probability that the pest will be distributed, as a result of the processing, sale or disposal of the commodity, in the PRA area and subsequently transfer to a susceptible part of a host.
  

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  distribution and incidence of the pest in the source area
  
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  occurrence of the pest in a life-stage that would be associated with the commodity
  
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  volume and frequency of movement of the commodity along each pathway
  
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  seasonal timing of imports
  
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  pest management, cultural and commercial procedures applied at the place of origin
  
  Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Method for PRA
  
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  speed of transport and conditions of storage compared with the duration of the lifecycle of the pest
  
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  vulnerability of the life-stages of the pest during transport or storage
  
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  incidence of the pest likely to be associated with a consignment
  
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  commercial procedures (e.g. refrigeration) applied to consignments during transport and storage in the country of origin, and during transport to Australia.
  

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  commercial procedures (e.g. refrigeration) applied to consignments during distribution in Australia
  
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  dispersal mechanisms of the pest, including vectors, to allow movement from the pathway to a host
  
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  whether the imported commodity is to be sent to a few or many destination points in the PRA area
  
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  proximity of entry, transit and destination points to hosts
  
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  time of year at which import takes place
  
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  intended use of the commodity (e.g. for planting, processing or consumption)
  
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  risks from by-products and waste.
  

Establishment is defined as the ‘perpetuation for the foreseeable future, of a pest within an area after entry’ (FAO 2004). In order to estimate the probability of establishment of a pest, reliable biological information (lifecycle, host range, epidemiology, survival, etc.) is obtained from the areas where the pest currently occurs. The situation in the PRA area can then be compared with that in the areas where it currently occurs and expert judgement used to assess the probability of establishment.

Factors considered in the probability of establishment in the PRA area include:

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  availability of hosts, alternative hosts and vectors
  
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  suitability of the environment
  
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  reproductive strategy and potential for adaptation
  
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  minimum population needed for establishment
  
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  cultural practices and control measures
  

Spread is defined as ‘the expansion of the geographical distribution of a pest within an area’ (FAO 2004). The probability of spread considers the factors relevant to the movement of the pest, after establishment on a host plant or plants, to other susceptible host plants of the same or different species in other areas. In order to estimate the probability of spread of the pest, reliable biological information is obtained from areas where the pest currently occurs. The situation in the PRA area is then compared with that in the areas where the pest currently occurs and expert judgement used to assess the probability of spread.

Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Method for PRA

Factors considered in the probability of spread include:

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  suitability of the natural and/or managed environment for natural spread of the pest
  
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  presence of natural barriers
  
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  potential for movement with commodities, conveyances or by vectors
  
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  intended use of the commodity
  
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  potential vectors of the pest in the PRA area
  
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  potential natural enemies of the pest in the PRA area.
  

In its qualitative PRAs, Biosecurity Australia uses the term ‘likelihood’ for the descriptors it uses for its estimates of probability of entry, establishment and spread. Qualitative likelihoods are assigned to each step of entry, establishment and spread. Six descriptors are used: high; moderate; low; very low; extremely low; and negligible (Table 2.1). Descriptive definitions for these descriptors and their indicative probability ranges are given in Table 2.1. The indicative probability ranges are only provided to illustrate the boundaries of the descriptors. These indicative probability ranges are not used beyond this purpose in qualitative PRAs. The standardised likelihood descriptors and the associated indicative probability ranges provide guidance to the risk analyst and promote consistency between different risk analyses.

Table 2.1: Nomenclature for qualitative likelihoods

Likelihood	Descriptive definition	Indicative probability (P) range
High	The event would be very likely to occur	0.7 < P ≤ 1
Moderate	The event would occur with an even probability	0.3 < P ≤ 0.7
Low	The event would be unlikely to occur	0.05 < P ≤ 0.3
Very low	The event would be very unlikely to occur	0.001 < P ≤ 0.05
Extremely low	The event would be extremely unlikely to occur	0.000001 < P ≤ 0.001
Negligible	The event would almost certainly not occur	0 ≤ P ≤ 0.000001

The likelihood of entry is determined by combining the likelihood that the pest will be imported into the PRA area and the likelihood that the pest will be distributed within the PRA area, using a matrix of rules (Table 2.2). This matrix is then used to combine the likelihood of entry and the likelihood of establishment, and the likelihood of entry and establishment is then combined with the likelihood of spread to determine the overall likelihood of entry, establishment and spread.

For example, if the probability of importation is assigned a likelihood of ‘low’ and the probability of distribution is assigned a likelihood of ‘moderate’, then they are combined to give a likelihood of ‘low’ for the probability of entry. The likelihood for the probability of entry is then combined with the likelihood assigned to the probability of establishment (e.g. ‘high’) to give a likelihood for the probability of entry and establishment of ‘low’. The likelihood for the probability of entry and establishment is then combined with the likelihood assigned to the probability of spread (e.g. ‘very low’)

to give the overall likelihood for the probability of entry, establishment and spread of ‘very low’.

Table 2.2: Matrix of rules for combining qualitative likelihoods

Time and volume of trade

One factor affecting the likelihood of entry is the volume and duration of trade. If all other conditions remain the same, the overall likelihood of entry will increase as time passes and the overall volume of trade increases.

Biosecurity Australia normally considers the likelihood of entry on the basis of the estimated volume of one year’s trade. This is a convenient value for the analysis that is relatively easy to estimate and allows for expert consideration of seasonal variations in pest presence, incidence and behaviour to be taken into account. The consideration of the likelihood of entry, establishment and spread and subsequent consequences takes into account events that might happen over a number of years even though only one year’s volume of trade is being considered. This difference reflects biological and ecological facts, for example where a pest or disease may establish in the year of import but spread may take many years.

The use of a one year volume of trade has been taken into account when setting up the matrix that is used to estimate the risk and therefore any policy based on this analysis does not simply apply to one year of trade. Policy decisions that are based on Biosecurity Australia’s method that uses the estimated volume of one year’s trade are consistent with Australia’s policy on appropriate level of protection and meet the Australian Government’s requirement for ongoing quarantine protection. Of course, if there are substantial changes in the volume and nature of the trade in specific commodities then Biosecurity Australia has an obligation to review the risk analysis and, if necessary, provide updated policy advice.

In assessing the volume of trade in this PRA, Biosecurity Australia assumed that a substantial volume of trade will occur.

2.2.3 Assessment of potential consequences

Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Method for PRA

potential consequences are given in Article 5.3 of the SPS Agreement (WTO 1995), ISPM 5 (FAO 2008) and ISPM 11 (FAO 2004).

Direct pest effects are considered in the context of the effects on:

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  plant life or health
  
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  other aspects of the environment
  

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  eradication, control, etc
  
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  domestic trade
  
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  international trade
  
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  environment.
  

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  Local: an aggregate of households or enterprises (a rural community, a town or a local government area).
  
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  District: a geographically or geopolitically associated collection of aggregates (generally a recognised section of a state or territory, such as ‘Far North Queensland’).
  
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  Regional: a geographically or geopolitically associated collection of districts in a geographic area (generally a state or territory, although there may be exceptions with larger states such as Western Australia).
  
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  National: Australia wide (Australian mainland states and territories and Tasmania).
  

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  Indiscernible: pest impact unlikely to be noticeable.
  
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  Minor significance: expected to lead to a minor increase in mortality/morbidity of hosts or a minor decrease in production but not expected to threaten the economic viability of production. Expected to decrease the value of non-commercial criteria but not threaten the criterion’s intrinsic value. Effects would generally be reversible.
  
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  Significant: expected to threaten the economic viability of production through a moderate increase in mortality/morbidity of hosts, or a moderate decrease in production. Expected to significantly diminish or threaten the intrinsic value of non-commercial criteria. Effects may not be reversible.
  
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  Major significance: expected to threaten the economic viability through a large increase in mortality/morbidity of hosts, or a large decrease in production. Expected to severely or irreversibly damage the intrinsic ‘value’ of non-commercial criteria.
  

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Table 2.3: Decision rules for determining the consequence impact score based on the magnitude of consequences at four geographic scales

The overall consequence for each pest is achieved by combining the qualitative impact scores (A–G) for each direct and indirect consequence using a series of decision rules (Table 2.4). These rules are mutually exclusive, and are assessed in numerical order until one applies.

Table 2.4: Decision rules for determining the overall consequence rating for each pest

2.2.4 Estimation of the unrestricted risk

(‘indiscernible’ at all four levels) was added. The rules for combining impacts in Table 2.4 were adjusted accordingly.

Draft PRA report for ‘Candidatus Liberibacter psyllaurous’ Method for PRA

When interpreting the risk estimation matrix, note the descriptors for each axis are similar (e.g. low, moderate, high) but the vertical axis refers to likelihood and the horizontal axis refers to consequences. Accordingly, a ‘low’ likelihood combined with ‘high’ consequences, is not the same as a ‘high’ likelihood combined with ‘low’ consequences – the matrix is not symmetrical. For example, the former combination would give an unrestricted risk rating of ‘moderate’, whereas, the latter would be rated as a ‘low’ unrestricted risk.

Table 2.5: Risk estimation matrix

2.2.5 Australia’s appropriate level of protection (ALOP)

Like many other countries, Australia expresses its ALOP in qualitative terms. Australia’s ALOP, which reflects community expectations through government policy, is currently expressed as providing a high level of sanitary or phytosanitary protection aimed at reducing risk to a very low level, but not to zero. The band of cells in Table 2.5 marked ‘very low risk’ represents Australia’s ALOP.

2.3 Stage 3: Pest risk management

The conclusions from pest risk assessment are used to decide whether risk management is required and if so, the appropriate measures to be used. Where the unrestricted risk estimate exceeds Australia’s ALOP, risk management measures are required to reduce this risk to a very low level. The guiding principle for risk management is to manage risk to achieve Australia’s ALOP. The effectiveness of any proposed phytosanitary measure (or combination of measures) is evaluated, using the same approach as used to

evaluate the unrestricted risk, to ensure it reduces the restricted risk for the relevant pest or pests to meet Australia’s ALOP.

ISPM 11 (FAO 2004) provides details on the identification and selection of appropriate risk management options and notes that the choice of measures should be based on their effectiveness in reducing the probability of entry of the pest.

Examples given of measures commonly applied to traded commodities include:

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  options for consignments – e.g., inspection or testing for freedom from pests, prohibition of parts of the host, a pre-entry or post-entry quarantine system, specified conditions on preparation of the consignment, specified treatment of the consignment, restrictions on end-use, distribution and periods of entry of the commodity
  
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  options preventing or reducing infestation in the crop – e.g., treatment of the crop, restriction on the composition of a consignment so it is composed of plants belonging to resistant or less susceptible species, harvesting of plants at a certain age or specified time of the year, production in a certification scheme
  
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  options ensuring that the area, place or site of production or crop is free from the pest – e.g., pest-free area, pest-free place of production or pest-free production site
  
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  options for other types of pathways – e.g., consider natural spread, measures for human travellers and their baggage, cleaning or disinfestation of contaminated machinery
  
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  options within the importing country – e.g., surveillance and eradication programs
  
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  prohibition of commodities – if no satisfactory measure can be found.