Project number:
2023-133
Project Status:
Current
Budget expenditure:
$130,349.30
Principal Investigator:
Brendan D. Cowled
Organisation:
AusVet Pty Ltd
Project start/end date:
18 Jul 2024
-
28 Feb 2025
Contact:
FRDC
TAGS
SPECIES
This project would utilise the combination of a systematic review of literature and industry consultation to provide a thorough risk assessment of AVG impacting other areas and industries. Risk analysis is a well-established scientific method and is commonly used by veterinary epidemiologists to allow objective assessment of the risks of animal production or harvest practices or trade in transmitting animal diseases. This project seeks to apply risk assessment to explore the risk that SRL fishers and other activities pose to transmission of AVG and what level of risk mitigation is required to manage that risk. It may be possible to relax fishing and movement restrictions if the risk can be mitigated, or wider consideration of more activities may lead to risk mitigation recommendations for various activities.
1. Assess the risk that Southern Rock Lobster fishing operations (the use of pots and fishing vessels) act as a vector of transmission of AVG.
2. Assess the risk that other commercial and non-commercial fishing activities act as a vector of transmission of AVG. This will include:• recreational fishing (including boating activities)• abalone fishing and associated activities such as cleaning abalone catch enroute to port• a representative net fishing industry.We note that the Victorian Government has completed a risk assessment on abalone diving and we will not repeat that, instead review their risk assessment and include that in our project to be efficient.
Final report
Authors:
Drs Isabel MacPhillamy
Emma Zalcman and Brendan Cowled
Final Report
•
2025-10-23
•
3.10 MB
2023-133-DLD.pdf
The objective of this project was to assess the likelihood of the following operations spreading AVG to areas with a naïve/susceptible population present:
1. Southern Rock Lobster fishing (using pots and fishing vessels)
2. Recreational sector (diving and line fishing)
3. Commercial abalone fishing
4. Commercial net fishing.
The scope of this desktop project was relatively narrow and conducted as commissioned by FRDC under advice from industry. It was commissioned to focus on the risks of the four pathways spreading AVG to new areas, along with suitable risk mitigations for those four pathways. Unfortunately, the project could not include new field based or experimental scientific research to address scientific uncertainties, or assess additional pathways such as natural spread, as these were not commissioned within the project. Therefore, the risk assessments could not assess the role of these four assessed pathways relative to natural spread pathways (e.g. in water currents), though natural spread pathways may (or may not) be significant. Instead, uncertainties around unaddressed pathways were discussed and future research needs highlighted to assist future decision making and future commissioning of research.
1. Southern Rock Lobster fishing (using pots and fishing vessels)
2. Recreational sector (diving and line fishing)
3. Commercial abalone fishing
4. Commercial net fishing.
The scope of this desktop project was relatively narrow and conducted as commissioned by FRDC under advice from industry. It was commissioned to focus on the risks of the four pathways spreading AVG to new areas, along with suitable risk mitigations for those four pathways. Unfortunately, the project could not include new field based or experimental scientific research to address scientific uncertainties, or assess additional pathways such as natural spread, as these were not commissioned within the project. Therefore, the risk assessments could not assess the role of these four assessed pathways relative to natural spread pathways (e.g. in water currents), though natural spread pathways may (or may not) be significant. Instead, uncertainties around unaddressed pathways were discussed and future research needs highlighted to assist future decision making and future commissioning of research.
The literature review and stakeholder consultations identified key research gaps regarding the epidemiology of AVG and how this relates to the transmission and spread of the disease. Based on these gaps, two scenarios were developed for the risk assessment. The scenarios were based on different sets of plausible biological assumptions.
For scenario A, we assume:
1. mucus plays no role in prolonging infectivity of HaHV-1
2. mucus is removed with the same detergents effective against other herperviruses
3. a large viral load is required for transmission to occur
4. the route of infection is via ingestion.
For scenario B, we assume:
1. mucus plays a role in prolonging infectivity of HaHV-1
2. mucus is difficult to remove and requires strong detergents and vigorous physical action to break down
3. a small viral load is required for transmission to occur
4. the route of infection is via immersion/gills.
For scenario A, we assume:
1. mucus plays no role in prolonging infectivity of HaHV-1
2. mucus is removed with the same detergents effective against other herperviruses
3. a large viral load is required for transmission to occur
4. the route of infection is via ingestion.
For scenario B, we assume:
1. mucus plays a role in prolonging infectivity of HaHV-1
2. mucus is difficult to remove and requires strong detergents and vigorous physical action to break down
3. a small viral load is required for transmission to occur
4. the route of infection is via immersion/gills.
The research gaps, especially around basic epidemiology of AVG (role of mucus in transmission, route of infection and viral load for transmission) led to considerable uncertainty in estimating the risks that various activities pose to AVG spread. If scenario A is true then there is generally a very low risk associated with activities, meaning few risk mitigation measures are required. If scenario B is true, then the risk of transmission associated with abalone and SRL fishing and recreational diving are high and risk mitigation measures are recommended. Thus a precautionary principle is recommended until further research occurs and resolves uncertainty. Therefore, the risk mitigation measures outlined in the South Australian and Victorian COP for the abalone and Southern Rock Lobster fisheries are relevant and should be maintained until this research occurs. Further research is required to determine where on the spectrum of scenario A and B the risks more accurately lie.
Further, any fishing activities that result in interaction with abalone habitats and potential transmission of HaHV-1 should be carefully managed. Early in an outbreak, when the extent of an outbreak is unknown, fishing should cease in declared areas (restricted and control areas), to manage transmission risks. However, after the outbreak is delimited, fishing in declared areas (i.e. the control area and those areas in the restricted area where there are no active outbreaks occurring – see Figure 1) may resume with risk mitigations. These mitigations will be around biosecurity practices and the movement of potentially contaminated abalone. Biosecurity practices required will focus on disinfection of boats and equipment before moving to uninfected areas to reduce the risk of fomite transmitted infection to new areas. That is, fishing can occur within uninfected areas within restricted areas, but boats must return to port and offload abalone (if abalone fisherman) and disinfect equipment (including drying and desiccation) before moving to clean areas (e.g. control areas, free areas and uninfected areas within the restricted area). Abalone from infected areas should be considered potentially infected even if they appear healthy when harvested from infected areas and great care taken in marketing.
It is important to realise this project scope did not include estimation of risks associated with natural spread (e.g. water currents, ocean upwellings etc.). This scope-stipulated-omission should be considered by stakeholders when assessing this project. If later research demonstrates that natural spread is much more significant than the four pathways considered here, then recommended risk mitigations would change. For example, imposing fishing restrictions in and around restricted and control areas would have little impact on transmission were natural spread to be significant. However, we have not assessed the evidence on natural spread or the comparative risks between this and the four pathways we assessed. We therefore cannot assess the relative importance of other spread pathways and therefore relative importance of competing risk mitigations. Research regarding the natural spread of Ostreid herpesvirus ranges from 10s of km to 100s of km depending on the location (Roberts et al. 2020). If this is found to be the case for HaHV-1, there may be a requirement for region specific recommendations.
As further research and data becomes available the risk assessment can be reviewed, with estimated likelihoods updated at relevant nodes to calculate new estimated risks. It is important that this occurs as new information becomes available to ensure risk mitigation advice is appropriate and contextually relevant.
The following areas of research have been recommended to address the research gaps and improve the accuracy of the risk assessment, and more optimal selection of risk mitigation measures:
• the role mucus plays in protecting and spreading the virus and what actions are required to break it down. Note that the CSIRO previously investigated mucus – they found that HaHV-1 could indeed be present in mucus and transmit virus to healthy abalone, but mucus did not enhance virus infectivity when in seawater. However, many important questions remain (e.g. does infected mucus assist fomite spread on equipment?).
• viral load produced during an outbreak, and subsequently required to induce transmission
• route of infection
• movement of HaHV-1 through the water column and other natural pathways.
• the role mucus plays in protecting and spreading the virus and what actions are required to break it down. Note that the CSIRO previously investigated mucus – they found that HaHV-1 could indeed be present in mucus and transmit virus to healthy abalone, but mucus did not enhance virus infectivity when in seawater. However, many important questions remain (e.g. does infected mucus assist fomite spread on equipment?).
• viral load produced during an outbreak, and subsequently required to induce transmission
• route of infection
• movement of HaHV-1 through the water column and other natural pathways.
The following research and activities are recommended to improve the abalone industry’s preparedness for future outbreaks:
• presence of latently infected populations and natural stress events required for clinical disease, shedding and subsequent transmission to occur
• modelling of the natural spread of the virus
• clear communication of measures and recommendations for biosecurity
• cost-benefit analysis of active surveillance activities to identify latently infected populations
• workshop with researchers to determine capacity and interest for further research.
• presence of latently infected populations and natural stress events required for clinical disease, shedding and subsequent transmission to occur
• modelling of the natural spread of the virus
• clear communication of measures and recommendations for biosecurity
• cost-benefit analysis of active surveillance activities to identify latently infected populations
• workshop with researchers to determine capacity and interest for further research.
