Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart

Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Benefits of Rabbit
                                                Biocontrol in Australia
                                             Tarnya Cox, Tanja Strive, Greg Mutze,
                                                    Peter West and Glen Saunders

Benefits of Rabbit Biocontrol in Australia
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Benefits of Rabbit
                 Biocontrol in Australia
                                                    Tarnya Cox1
                                                   Tanja Strive2
                                                    Greg Mutze3
                                                    Peter West1
                                                 Glen Saunders1

     Vertebrate Pest Research Unit, Department of Primary Industries
                                   Locked Bag 6006, Orange NSW 2800
                                Division of Ecosystem Sciences, CSIRO
                                    GPO Box 1700, Canberra ACT 2600
Natural Resources Management Biosecurity, Biosecurity South Australia
                                     GPO Box 1671, Adelaide SA 5001


                                      An Invasive Animals CRC Project
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Benefits of Rabbit Biocontrol in Australia

Disclaimer: The views and opinions expressed in this report reflect those of the author and do not
necessarily reflect those of the Australian Government, Invasive Animals Ltd, or the Invasive Animals
Cooperative Research Centre. The material presented in this report is based on sources that are
believed to be reliable. Whilst every care has been taken in the preparation of the report, it is “as is”,
without warranty of any kind, to the extent permitted by law.

Published by: Invasive Animals Cooperative Research Centre.
Telephone: (02) 6201 2887
Facsimile: (02) 6201 2532

ISBN: 978-1-921777-63-9
Web ISBN: 978-1-921777-64-6

© Invasive Animals Cooperative Ltd 2013
This work is copyright. The Copyright Act 1968 permits fair dealing for study, research, information or
educational purposes. Selected passages, tables or diagrams may be reproduced for such purposes
provided attribution to the owner is acknowledged. Major extracts of the entire document may not be
reproduced by any process.

The IA CRC gratefully acknowledges funding support from the Australian Government through its Caring
for our Country program for the IA CRC rabbit research and the publication of this document.

This document should be cited as: Cox TE, Strive T, Mutze G, West P and Saunders G (2013). Benefits
of Rabbit Biocontrol in Australia. PestSmart Toolkit publication, Invasive Animals Cooperative Research
Centre, Canberra, Australia.
Front cover photo: G. Chapman, CSIRO.
Available online at:

ii                                                                              Invasive Animals CRC
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart

Executive Summary ..........................................1
  Project terms of reference ................................... 8
  Overview of rabbit distribution, abundance and impacts
  ..................................................................... 8
Benefits of current rabbit biocontrol technology ... 14
  Environmental benefits ......................................15
  Social benefits .................................................15
  Economic benefits .............................................15
General benefits of future rabbit biocontrol
technology ................................................... 16
Current rabbit biocontrol initiatives ................... 18
                                                                                       Image: Rabbit plague on Wardang Island in 1963
  RHD-Boost .......................................................18
                                                                                               (Source: National Archives of Australia)
     Strain selection ............................................18
     Overcoming immunity to existing RHDV strains .....19
     Interfering endemic non-pathogenic caliciviruses
     RCV-A1 .......................................................20
     Overcoming genetic resistance in wild rabbits ......21
     RHD-Boost Release and Performance Measurement 21                       Reducing risks associated with future RHDV strain
     Measuring Impact ..........................................21          releases ....................................................... 27

     Integrating conventional control .......................21                  RHD-Boost Release and Performance Measurement . 27

     Impact of RHD-Boost ......................................22                Maximising RHD Boost impact by optimising release of
                                                                                 new RHDV strains when RCV-A1 prevalence is low .. 27
     Benefits of RHD-Boost ....................................22
                                                                                 Building and maintaining diagnostic capability to track
  RHD Resistance Model ........................................22                biocontrol performance .................................. 27
  RHD Accelerator ...............................................23         Conclusions and recommendations ..................... 28
     Objective and rationale ..................................23           References ................................................... 29
     Replicating natural selection ...........................23            Appendix 1: Background information on rabbit
     Impact of RHD Accelerator ...............................24            biocontrol agents ........................................... 32
     Benefits of RHD Accelerator .............................24                 Myxomatosis ................................................ 32
  Bioprospecting .................................................24             Rabbit fleas ................................................. 32
     Objective and rationale ..................................24                Rabbit haemorrhagic disease ............................ 32
     Impact of Bioprospecting ................................25                 Virally-vectored immunocontraception ............... 33
     Benefits of Bioprospecting ...............................25           Appendix 2: Diagrammatic representation of benefits
  Technology opportunity ......................................25
                                                                            from RHD Boost, RHD Accelerator, Bioprospecting
                                                                            and DSS/Rabbit Facilitator ................................ 34
  Environmental and economic benefits of new biocontrol
  technologies ....................................................26

 Benefits of Rabbit Biocontrol in Australia                                                                                             iii
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
iv   Invasive Animals CRC
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Executive Summary                                          Myxomatosis – MV, a highly infectious poxvirus disease
                                                           which causes severe generalised disease in European
                                                           rabbits. It was introduced in to Australia in 1950 as a
EUROPEAN RABBITS (Oryctolagus cuniculus) are a             biocontrol agent for rabbits.
severe continental-scale threat to Australia’s globally
important biodiversity and agriculture. The extreme        Rabbit Haemorrhagic Disease – RHD, a highly
sensitivity of many native plant species to rabbit         infectious disease specific to European rabbits caused
damage – as few as one rabbit per hectare can impede       by the calicivirus Rabbit Haemorrhagic Disease Virus
natural regeneration - has resulted in 75 nationally       (RHDV). It escaped quarantine in Australia in 1995
threatened plant species and five threatened               and was subsequently released as a biocontrol agent
ecological communities being at risk from rabbit           from 1996 to the present day.
impacts. Rabbits are also Australian agriculture’s most
costly vertebrate pest animal causing more than $200       continued persistence of many native threatened
million in production losses each year.                    species, large scale carbon biosequestration, and
                                                           improved landscape and ecosystem resilience. The
Without rabbit biocontrol agents, however, these           cumulative economic benefits for agriculture alone
impacts would be much worse: the combination of            from MV and RHDV over 60 years are estimated at $70
myxoma virus (MV) and rabbit haemorrhagic disease          Billion, or an average of $1.17 billion per year.
virus (RHDV) still limits rabbit numbers to about 15% of
their potential numbers, and without them the cost for     To maintain these benefits and keep rabbit abundance
agriculture alone would be in excess of $2 billion a       below or near the rabbit impact threshold, strategic
year. The cumulative environmental benefits of the         rabbit biocontrol research is critical to strengthen the
release of MV in 1950 and RHDV in 1995 includes            effectiveness of existing rabbit biocontrol agents, and
landscape scale native vegetation regeneration,            identify and evaluate new potential biocontrol agents.
increased abundance of native plants and animals,          This is being partially progressed through three key

Benefits of Rabbit Biocontrol in Australia                                                                    1
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Rabbit Calicivirus Australia-1 – RCV-A1, a pre-existing
initiatives in the Invasive Animals CRC rabbit research    benign calicivirus which causes no disease and offers
program (2012-17):                                         rabbit’s partial protection to infection by the
                                                           introduced pathogenic calicivirus RHDV. RCV-A1 is
1. RHD Boost – selection and evaluation of naturally       mainly found in the cool-wet regions of Australia with
   occurring overseas RHDV strains shown to have           > 400mm annual rainfall.
   improved effectiveness over the one endemic
   RHDV strain introduced in 1995,
2. RHD Accelerator – proof of concept for a platform       In the medium term, there is an urgent need to
   technology to continuously develop new RHDV             develop a coordinated program of rabbit disease
   strains through accelerated natural selection, and
                                                           monitoring and surveillance across the various climatic
3. Bioprospecting - identify and assess feasibility of
   new potential biocontrol agents.                        regions of the Australian continent to understand
                                                           prevalence, seasonal fluctuations and interactions of
This research program has been designed to deliver         rabbit pathogens such as RHDV, MV and the interfering
strengthened RHDV strains from about 2015 to 2030,         benign calicivirus RCV-A1. Understanding these
augmented by any new evaluated biocontrol agents           mechanisms is critical to identifying the factors that
from about 2030. The benefits of these three               define the success of potential biocontrol/biocide
technologies are summarised below. The predicted           releases. An integral component of this is to ensure
impact of these technologies on rabbit abundance is        availability of state-of-the-art differential diagnostic
outlined in four scenarios in the graph above:             tools and epidemiological modelling. Capabilities in
Scenario 1: Business as usual shows an on-going            these areas need to be increased and maintained.
increase in rabbit abundance that erodes all the gains     In the longer term it is essential to ensure that applied
from RHDV and leads to major increases in economic
                                                           biocontrol research can continue. If successful in their
and environmental impacts over time.
                                                           proof of concept stages, the RHD-Accelerator and the
Scenario 2: Release of new RHD-Boost RHDV strains
regains most of the benefits of the original RHDV          Bioprospecting projects will need ongoing support to
release, followed by a progressive increase in rabbit      be further developed to the product stage. In addition,
abundance                                                  scientific research needs to continue to increase our
Scenario 3: Release of new RHD-Boost RHDV strains          understanding of the long term effects of evolution and
followed by new RHD-Accelerator RHDV strains which         genetic resistance development, as well as cumulative
regain the benefits of the RHD-Boost release.              or neutralising effects that may arise from co-occurring
Subsequent releases of RHD-Accelerator strains every       pathogens. The latter is of particular importance as
5-10 years see a repeated relative knockdown in rabbit     more and more pathogens and viral variants are added
                                                           to the environment. This need is reinforced by the
Scenario 4: Releases of new RHD-Boost RHDV strains
                                                           National Biosecurity Research and Development
followed by new RHD-Accelerator RHDV strains and a
                                                           Capability Audit commissioned by the National
new biocontrol agent have the greatest impact on
                                                           Biosecurity Committee, which suggested that Australia
rabbit numbers.
                                                           should invest more heavily in the long term funding of
While this balanced research portfolio aims to deliver a   biological control programs, including monitoring of
rabbit biocontrol technology pipeline in the short to      field effectiveness.
medium term, there remain important gaps that create
                                                           The imperative for strategic rabbit biocontrol research
significant risk to the effectiveness of these research
                                                           is based on four facts: rabbits are becoming
outputs and the seamless continuation of effective
                                                           increasingly resistant to existing rabbit biocontrol
rabbit biocontrol. In the short term, knowledge gaps of
                                                           agents, in good seasons rabbit populations can increase
the seasonal patterns of the endemic benign rabbit
                                                           7–10 fold, rural populations and labour continues to
calicivirus (RCV-A1) remain, which is critical to ensure
                                                           decrease, and the cost of rural labour continues to
impacts from the release of RHD-Boost strains are
                                                           increase. Proactive investment in strategic rabbit
maximised by knowing when the impeding RCV-A1 virus
                                                           biocontrol research will ensure rabbit abundance can
is least prevalent in a landscape. Additional resources
                                                           be kept near the rabbit impact threshold which is less
also need to be secured to enable the performance and
                                                           than one rabbit per hectare.
benefits of RHD Boost strains to be quantitatively
measured in various landscapes.
2                                                                                     Invasive Animals CRC
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart
Improved RHDV     Objective                    Benefits

RHD Boost         Identify, seek approval,     Net Present Value: $1.4 Billion over 15 years made up of $840
rollout           release and selectively      million of agricultural benefits and $560 million in carbon
                  measure the performance      sequestration benefits.
                  of new naturally
                                               Benefit Cost Ratio: 563 to 1
                  occurring overseas RHDV
                  strains found to be          Internal Rate of Return: 217%
                  superior to the one
                                               Biodiversity benefits: increased regeneration of native vegetation,
                  existing RHDV strain in
                                               and in longer term increase in abundance of many threatened
                                               Carbon benefits: increase in standing biomass via regeneration
                                               Soil benefits: reduced soil erosion and land degradation
                                               Assumes selection and release about 2015

RHD               Develop a platform           Net Present Value: $79 million over 15 yrs and $300 million over 30
Accelerator       technology for on-going      years (60% are agricultural benefits, 40% carbon sequestration
platform          laboratory based             benefits)
technology        selection of superior
                                               Benefit cost Ratio: 48 to 1 over 15 yrs
                  RHDV strains
                                               Internal Rate of Return: 38%
                                               Biodiversity benefits: increased regeneration of native vegetation,
                                               and in longer term increase in abundance of many threatened
                                               Carbon benefits: increase in standing biomass via regeneration
                                               Soil benefits: reduced soil erosion and land degradation
                                               Assumes new RHDV strains able to sustain the benefits delivered
                                               by RHD Boost

Comprehensive     Understanding the nature     Improves effectiveness of RHD Boost and RHD Accelerator
RHD resistance    and geographical             technologies
model             distribution of rabbit
                  genetic resistance, to
                  develop a framework for
                  the optimisation of
                  additional virus releases

New biocontrol
agents assessed

Assessment and    Assess the feasibility of    Net Present Value: $28 million over 30 years
prospecting for   new potential rabbit
                                               Benefit Cost Ratio: 115 to 1
potential new     biocontrol agents and
biocontrol        establish an international   Internal Rate of Return: 21.5%
agents            alert network
                                               Assumes additional research of new biocontrol agent to enable
                                               release from 2030.

Benefits of Rabbit Biocontrol in Australia                                                                           3
Benefits of Rabbit Biocontrol in Australia - Tarnya Cox, Tanja Strive, Greg Mutze, Peter West and Glen Saunders - PestSmart


    Native grass regeneration post RHDV arrival and rabbit control on Thackaringa Station,
    Broken Hill. The regeneration occurred during a period of drought (Images: David Lord).

4                                                                          Invasive Animals CRC
Exclusion fencing showing the change in vegetation structure due to rabbits on Macquarie
          Island (top) and in Coorong, SA (bottom) (Images: Brian Cooke).

Benefits of Rabbit Biocontrol in Australia                                                           5
Native plants wich are especially susceptible to browsing by rabbits, even at low rabbit
    densities. Top left: Myporum insulare, Boobiala, Coorong SA; Top right: Acacia ligulata,
    Sandhill wattle, Hattah-Kulkyne National Park, VIC; Bottom left: rabbit damage to tree
    guard and sheoak; Bottom right and left: rabbit damage to Allocasuarina and Callitris sp.,
    Hattah-Kulkyne National Park, VIC. (Images: Brian Cooke).

6                                                                              Invasive Animals CRC
This Melaleuca lancelota grew during a period of rabbit relief after the spread of MV. Note
         the lack of understory and the browsing at rabbit height. Increases in rabbit numbers are
         winding back any gains made by the releases of MV and RHDV (Image: Brian Cooke).

Benefits of Rabbit Biocontrol in Australia                                                             7
The 2009-10 Caring for our Country business plan
included a priority outcome to reduce rabbit impacts
with the following key target:
      to suppress rabbit populations over the
      next three years to densities that are low
      enough to allow regeneration and recovery
      of critically endangered and endangered
      species and communities in identified
      priority areas.
To achieve this outcome, the investment portfolio
included $1.5 million of the $2.7 million required for
the RHD-Boost project. The RHD-Boost project aimed
to identify and evaluate new naturally occurring
overseas strains of rabbit haemorrhagic disease virus
(RHDV) - the causative agent of rabbit haemorrhagic       benign and lethal varieties of RHD and myxomatosis
disease (RHD) - which were suitable for release into      (MV).
Australian rabbit populations and which sought to
overcome the developing acquired immunity and
                                                          Overview of rabbit distribution, abundance
genetic resistance to the current Czech 351 RHDV          and impacts
strain, and the impact of the benign calicivirus Rabbit   Wild rabbits were successfully introduced into Australia
Calicivirus Australia 1 (RCV-A1) which offers partial     in 1859 and within 70 years had spread to inhabit 70%
protection to infection by pathogenic RHDV.               of Australia’s landmass (5.3 million km 2) (Figures 1 and
This report reviews previous biological control efforts   2). They are widespread throughout most locations
for rabbits in Australia, the likely economic and         where they are found (NLWRA and IACRC 2008).
environmental benefits of the release of a new strain/s   Rabbits feeding habits include removing vegetation to
of RHDV (RHD-Boost), and the benefits of investing in     ground level and digging for roots which can result in
future areas of rabbit biocontrol research such as the    significant soil destabilisation and erosion, leading to
development     of    a    performance      management    the desertification of heavily impacted areas. Such
framework (RHD-Boost Release and Performance              damage is added to through the excavation of warren
Measurement), the ongoing selection of improved RHDV      systems – often extensive and in ecologically sensitive
strains (RHD-Accelerator), the continued search for       areas. Rabbits are also prolific breeders. In good
new biocontrol agents (Bioprospecting) and It also        seasons populations can increase 7–10 fold. Rabbits
describes current knowledge about the distribution of     impact 75 Commonwealth Environment Protection and
rabbits, and benign rabbit calicivirus (RCV-A1).          Biodiversity Conservation Act 1999 listed threatened
                                                          plant species and five threatened ecological
Project terms of reference                                communities (Figure 3) and are the most costly pest
This project’s statement of work required Invasive        animal to agricultural production: the annual cost
Animals Ltd to undertake a desk top evaluation of a       exceeding $200 million (Gong et al. 2009).
successful release of an additional effective rabbit
biocontrol agent. The evaluation was to include the
likely benefits to production and the environment
based on a literature review, historical information
about the 1990’s release of RHD, and current
knowledge about the distribution of rabbits and the

8                                                                                    Invasive Animals CRC
Figure 1: Reported abundance of European rabbits (Oryctolagus cuniculus) across Australia
 (Source data: Invasive Animals CRC, RabbitScan, and NLWRA and IACRC 2008).

Benefits of Rabbit Biocontrol in Australia                                                   9
Figure 2: Rate of spread of wild rabbits since their introduction to Geelong, Victoria in 1859 to their current
     known distribution (Source data: Invasive Animals CRC, Stoddard and Parer 1988).

10                                                                                      Invasive Animals CRC
Figure 3: Locations of critically endangered and endangered communities and species that may be
       adversely affected by rabbits (Commonwealth of Australia 2008).

Benefits of Rabbit Biocontrol in Australia                                                               11
Brief history of rabbit invasion and rabbit           Recent research conducted by the Invasive Animals
                 biocontrol pipeline                       Cooperative Research Centre (IA CRC) has shown that
     (adapted from Department of Environment and           Australian native vegetation is very sensitive to rabbit
                  Primary Industries 2011)                 damage. A specific example is Mulga (Acacia aneura)
                                                           which occurs across vast areas of central Australia.
                                                           Recruitment of seedlings for this species is greatly
 1859    24 wild rabbits released at Barwon Park near
         Geelong,     Vic,    for   hunting      become    impacted upon by rabbit densities as low as 1
         established. Invasion across Australia at about   rabbit/km2 (Mutze et al. 2008). This greatly impedes
         130 km per year. Some farms abandoned as          natural regeneration. Similar stories can be told for a
         early as 1881                                     variety of palatable trees and shrubs across much of
                                                           the distribution of the rabbit (Sandell 2002, Murdoch
 1926    Estimated 10 billion rabbits in Australia with
         70% of continent invaded                          2005, DEWHA 2008, Bird et al. 2012, Cooke 2012).

 1950    World’s first vertebrate pest biocontrol -        While the direct impact of rabbits on vegetation is
         myxoma virus (MV) - released and kills 99.8%      obvious, their impact on native animals via competition
         of infected rabbits                               is less so. For example, both kangaroo (Macropus
                                                           rufus, M. fuliginosus & M. robustus) and wombat
 1969    Rabbit flea species (Spilopsyllus cuniculi)
         approved for release to act as an improved        (Vombatus ursinus) numbers increased following native
         vector to spread MV in areas low in               vegetation regeneration after the release of RHDV,
         mosquitoes                                        suggesting that high populations of rabbits may restrict
                                                           these species (Mutze et al. 2008; Bird et al. 2012).
 1990    Rabbit population about 600 million
                                                           Rabbit impact on native pastures affects a variety of
 1993    Spanish rabbit flea (Xenophsylla cunicularis)
                                                           other species, including endangered or critically
         adapted for arid conditions approved for
         release and improves transmission of MV           endangered species such as the plains-wanderer
                                                           (Pedionomus torquatus) (Baker-Gabb 2002) and the
 1995    Rabbit haemorrhagic disease virus (RHDV)          golden sun moth (Synemon plana) (Clarke and O'Dwyer
         introduced and kills up to 98% of rabbits in
                                                           2000). Competition and land degradation by rabbits is
         arid areas
                                                           listed as a Key Threatening Process under the
 2000s Rabbits begin to develop resistance to RHDV         Commonwealth       Environmental    Protection    and
       infection.     Increasing    resistance    and      Biodiversity Conservation Act 1999.
       increasing food availability as drought breaks
       results in observed increasing rabbit numbers       The general trend in rabbit abundance across Australia
                                                           is upward. Figure 4 summarises information available
 2009    Benign endemic rabbit calicivirus (RCV-A1)
                                                           on changes in rabbit numbers in the arid pastoral area
         that confers partial protection to rabbits
         discovered and characterised                      of north-eastern South Australia associated with the
                                                           introduction of MV, then RHDV in an area where other
 2009+ New naturally occurring overseas RHDV               control measures, such as poisoning and warren ripping
       strains that have observed increased lethality      were not often applied. In that region, where
       to rabbits are imported from Europe and Asia
                                                           mosquitoes were scarce, the release of European
       and evaluated as part RHD Boost project co-
       funded through Caring for our Country               rabbit fleas (Spilipsyllus cuniculus) in 1969 enhanced
       Program                                             the spread of MV. Importantly, it shows a marked
                                                           increase in rabbit abundance since the early 2000s.
 2012    Successful Invasive Animals CRC extension
         includes strategic rabbit biocontrol research
         program to boost effectiveness of RHDV,
         assess feasibility of new potential rabbit
         biocontrol     candidates,   and    increased
         capabilities to promote regional integrated
         rabbit control

12                                                                                   Invasive Animals CRC
Figure 4: Diagram showing how rabbit abundance in semi-arid South Australia has varied through time in
   response to the release of biological control agents and the estimated Australia-wide economic losses to
   rabbits (black triangles). Scale for losses shown on right-hand side of figure (Cooke et al. 2013).

Benefits of Rabbit Biocontrol in Australia                                                                    13
Benefits of current rabbit biocontrol technology
By far the most successful method of reducing rabbit            The benefits of rabbit biocontrol are not uniform across
impacts in Australia has been the use of biological             Australia. This is particularly the case for RHDV, which
control agents. At times these have reduced rabbit              was generally more effective in drier, lower rainfall
numbers in some areas by as much as 99 per cent.                areas (Figure 5). Monitoring of rabbit abundance
Their impact has allowed land managers to apply                 showed an average decrease by two-thirds (67.3%) in
complementary conventional control techniques (e.g.             low rainfall areas, and only a quarter (27.5%) in high
warren ripping, baiting and fumigation) in a more cost          rainfall areas.
efficient and effective manner.         The continued
                                                                The application of biocontrol agents has a number of
suppression    of    recovering    and/or     reinvading
                                                                benefits, particularly when applied to large-scale pest
populations with biocontrol agents post conventional
                                                                problems such as that presented by the European
control has also been of benefit, greatly improving the
                                                                rabbit in Australia. The benefits of using biocontrol
value of applied conventional control. Australia has
                                                                can be counted in environmental, social and economic
introduced four biocontrol agents for rabbits over the
                                                                terms and, in the case of biocontrol for rabbits, is the
last 60 years: two viral diseases and two insect vectors
                                                                most cost effective way of managing a pest species.
to aid their transmission, and undertaken extensive
research into another: virally-vectored immuno-
contraception (Hardy et al 2006, Saunders et al 2010).
Background information is provided in Appendix 1.

       Figure 5: The decline in rabbit populations by rainfall zone after the arrival of RHDV.

14                                                                                         Invasive Animals CRC
Environmental benefits
The environmental benefits of RHDV were high,                One negative social impact of effective rabbit
especially in semi-arid areas where significant              biocontrol is that rabbits have lost some of their public
regeneration of native vegetation occurred, despite          profile as a major pest species. An increasing
below average rainfall (Sandell 2002, Murdoch 2005,          percentage of both the urban and rural population do
Mutze et al. 2008, Bird et al. 2012, Figure 5). After        not remember pre-RHDV or pre-MV rabbit numbers and
the introduction of RHDV, studies have shown that            damage. This has reduced the general awareness of
populations of native animals also increased.                rabbits as a problem, which in turn often results in
                                                             diminished public support for ongoing rabbit research
Populations of Spinifex hopping mice (Notomys alexis)        and control.
and plains mice (Pseudomys australis) (Read 2003),
common wombats (Vombatus ursinus), red kangaroos             Economic benefits
(Macropus rufus) and western grey kangaroos (M.
fuliginosus) (Mutze et al. 2008) all showed signs of         Recent estimates value the cumulative benefit of MV
recovery post RHDV introduction. Fox and feral cat           and RHDV to Australia’s pastoral industries at
numbers decreased in the Flinders Ranges National            approximately AU$70 billion over the last 60 years
Park after the rabbit population was reduced by 85%          (Cooke et al. 2013). In the period immediately after
(Holden and Mutze 2002). The most notable impact was         its release, MV resulted in AU$68 million in increased
on feral cats with their body condition falling by 17%.      production (AU$48 million in increased wool clips and
                                                             AU$20 million in increased sheep and lamb meat)
Social benefits                                              (Sobey 1981). The economic savings generated by
                                                             RHDV are estimated to be in excess of AU$350 million
There has been very little systematic research into the      annually, indicating that in the 17 years since its
social impacts of rabbits or any other vertebrate pests      release RHDV has generated benefits of almost AU$6
in Australia (Fitzgerald and Wilkinson 2009). It is likely   billion to the rural industries alone (Cooke et al. 2013).
that the effects of pest animals, for the most part, are     Considering that government and industry investment
economic and environmental, but there are flow-on            for the introduction of RHDV was in the order of AU$12
social impacts. A collection of personal stories (Quealy     million (Cooke et al. 2013) this return on investment is
2011) recounts that prior to the introduction of MV          unmatched by any other investments in rabbit control
many farmers and their families were forced to walk          research, or perhaps any other area of government
away from their properties because of the rabbit.            investment, in the last 50 years.
Many talk of the psychological distress at having to
make a new life away from the farm. Similarly,               When MV was first released it provided an estimated
competing interests lead to conflict between those           $1.4 billion p.a. benefit (2011 A$) (Cooke et al. 2013).
prospering from high rabbit numbers e.g. commercial          MV and RHDV combined reduce rabbit numbers by 85%
harvesters, and those suffering because of the rabbit.       compared to their potential numbers, a benefit that
                                                             would be lost if there was no biocontrol. If the initial
A case study of the social impacts of rabbits in the         myxo knockdown is used as a baseline, the current
Hunter Valley region of NSW in 2009 highlighted that         benefit of biocontrol is 85% of $1.4 billion or some
residents in this area were more concerned with the          $1.19 billion p.a. This equates with the average
impact of rabbits on mine rehabilitation sites, damage       estimated annual benefit of $1.17 billion derived from
to grape vines and the risk of injury to horses due the      the calculated $70 Billion benefit over 60 years from
presence of warrens (Fitzgerald and Wilkinson 2009).         MV and RHDV (Cooke et al. 2013). In comparison,
While this region is not necessarily representative of       without rabbit biocontrol, the estimated national
the attitudes of the whole of the area of Australia          impact of some 10 billion rabbits caused livestock
where rabbits occur, it does highlight the shift in          production losses of $2 billion/yr (Department of
attitude, by some, from a concern about the impacts of       Environment and Primary Industries 2011, Cooke et al.
rabbits on making a living, to a concern about the           2013).
impacts of rabbits on their living amenity.

Benefits of Rabbit Biocontrol in Australia                                                                        15
General benefits of future rabbit biocontrol
Rabbit control is costly, especially in pastoral areas,      of rabbit control as one of its objectives. The conduct
and many pastoralists believe that investment in             of research to maximise the effectiveness of existing
conventional controls such as rabbit warren ripping is       biocontrols, and the investigation of new biocontrols, is
not feasible (e.g. in sand hill country) and gains in        a high priority, long term action under the TAP.
production are unlikely to meet costs.         There is
                                                             While investment risk in the Bioprospecting model
therefore a continuing demand for the persistent use of
                                                             depends on the chance of finding another pathogen or
biological control agents as the only plausible solution
                                                             agent, Australia is well placed in that rabbits are an
to current residual rabbit problems in arid areas.
                                                             introduced species, unrelated to any other domestic or
Furthermore, biological control agents are usually the
                                                             native species, and in that context the risk of harming
only means of limiting rabbit damage in conservation
                                                             non-target species by a rabbit pathogen are reduced.
areas because of the high cost and the potential
                                                             In terms of RHD-Accelerator, the development of a
damaging impact of conventional control.
                                                             platform technology to sustainably address the rabbit
Biological control research is high risk in that potential   problem can be expected to greatly enhance
new pathogens would need to be discovered first and          profitability and ecological sustainability in the long
then imported into Australia under strict regulatory         term. The current RHD-boost project if successful will
requirements. However the benefits can be extremely          provide a net present value of over $1.4 billion over a
high as demonstrated by the economic returns. The            15 year period (Agtrans Research 2009). This value is
principal benefits of continuous investment into             likely to be an underestimation as the benefits to
biocontrol research are (Agtrans Research 2009):             biodiversity were not valued.
     Increased pasture biomass for animal production;        The impact of biocontrol on rabbit populations in
     Decreased effort and cost associated with               Australia has been significant. Continued investment in
     traditional rabbit control measures;                    biocontrol and the roll-out of variations of existing
     Increased ground cover leading to decreased soil        agents or the release of new agents is expected to
     erosion;                                                capitalise on previous gains made by MV and RHDV
     Improved native vegetation and associated               (Figure 6). If no further investment in biocontrol is
     habitats;                                               made, then rabbit numbers will continue to increase
     Increased carbon sequestration, and                     and all gains from RHDV will be eroded. The release of
     Improved biodiversity.
                                                             additional strain of RHDV are expected to reduce rabbit
The introduction of new and/or additional biocontrol         numbers close to where they were following the
agents to control vertebrate pests is the most cost          original RHDV release; however rabbit numbers will
effective way of conserving biodiversity when analysed       eventually begin to increase again. Investment in the
against all other mechanisms (Morton et al. 2002,            RHD-Accelerator project will see the release of strains
Possingham et al. 2002). New or additional agents            that will regain the benefits seen by the release of
would supplement existing agents (MV, rabbit fleas and       RHD-Boost. The impact of the release of a new
RHDV) and avoid serious resurgence of rabbits in a           biocontrol agent in conjunction with these other
timely way. The Threat Abatement Plan for                    efforts will ensure maximum impact on rabbit numbers.
Competition and Land Degradation by Rabbits (TAP)
                                                             Continued investment in biocontrol agents will have
(Department of the Environment, Water, Heritage and
                                                             benefits to the environment through increased standing
the Arts (DEWHA) 2008) lists the improvement of
                                                             biomass and therefore an increase in carbon
efficacy, target specificity, integration and humanness
                                                             sequestration (Fitzgerald and Wilkinson 2009). While

16                                                                                      Invasive Animals CRC
there is currently no specific published research on        increase in biomass would have on the wildlife ecology
assessing the carbon sequestration benefits of rabbit       in these areas is not quantified.
control, estimations are available. A 70% reduction in
                                                            Without continued investment in rabbit biocontrol, it is
rabbit numbers could see a benefit of up to $34 million
                                                            expected that the subsequent increase in rabbit
in carbon sequestration based on the government
                                                            numbers will result in an increase in the biodiversity
carbon price of $20 per tonne (Table 1). This could
                                                            impacts of rabbits, along with a reduction in carbon
increase to $45 million if an 85% reduction was
                                                            sequestration as the regeneration of woody perennials
achieved (Agtrans Research 2009). The impact this
                                                            declines (Fitzgerald and Wilkinson 2009).

   Figure 6: General trends in rabbit numbers since the release of myxomatosis in (1950) and projected
   benefits of future releases of biocontrol agents into the Australian rabbit population. The abundance
   baseline was arbitrarily set at an index level of 100 prior to myxomatosis. Pre-RHD figures are based on
   spotlight counts and established relationships between rainfall and rabbit abundance, and an average 90%
   reduction due to the initial impact of myxomatosis.

    Table 1: Assumed impacts of a reduction in rabbit numbers on carbon sequestration (Agtrans Research 2009).

                            Assumption of tonne/ha saved              Area of           Valued CO2 equivalent
   % Rabbit removal
                                with rabbit reduction              sequestration           at $20 per tonne

            85                             0.14                    1.5 million km2             $42 million

            70                            0.115                    1.5 million km2            $34.5 million

Benefits of Rabbit Biocontrol in Australia                                                                       17
Current rabbit biocontrol initiatives
Rabbits are a key species of interest of the new
Invasive Animals CRC (2012–17). The IA CRC strategic
rabbit biocontrol technology pipeline is focussed on           The RHD-Boost project was developed to address
two objectives: 1. Increasing the effectiveness of             increasing evidence that rabbit numbers are building
RHDV, and 2. Identifying feasible new biocontrol agents        up again after the 15 year long respite provided by the
that warrant further investment.                               initial release of RHDV. The follow on RHD-Boost
                                                               Release and Performance Measurement project builds
The three rabbit biocontrol technology projects
                                                               on the work undertaken in the RHD-Boost project and
specifically aimed at improving the biological control
                                                               is designed to undertake a performance management
of rabbits in Australia are:
                                                               evaluation of how differing strains of RHDV interact in
     RHD Boost and RHD Boost             Release     and       the environment.
     Performance Measurement
                                                               Strain selection
     RHD Accelerator
                                                               RHD Boost aims to identify new RHDV strains with high
     Bioprospecting for    a    new   potential    rabbit
                                                               lethality to rabbits immune due to the endemic RCV-
     biocontrol agent.
                                                               A1 and rabbits that are genetically resistant to
The impact of the IA CRCs rabbit portfolio will increase       infection with Czech 351 derived RHDV strains.
over time and vary across climatic regions (Table 2).
The objective, prospective benefits and technology             To select the most appropriate strain for release in
opportunities for the three biocontrol technologies is         Australia, a number of overseas strains of RHDV were
discussed below and a diagrammatic representation of           evaluated. The overseas strains had to show evidence
the benefits of each of the projects can be found in           of high mortality in the field and the ability to
Appendix 2.                                                    outcompete existing field strains and the benign RCV-
                                                               A1. More than 10 of these candidate strains, including
                                                               antigenic varieties (RHDVa), were imported into
                                                               Australia for evaluation under quarantine conditions.

  Table 2: Estimates of changing impacts in future by climatic zones with the IA CRC investment (Agtrans Research

                                 High rainfall                Wheat Sheep Zone           Pastoral Zone

   Reduction in Rabbit Impact    50% in 2014/15 compared      50% in 2014/15             70% in 2014/15 compared
                                 to impacts assumed for       compared to impacts        to impacts assumed for
                                 2013/14 in the               assumed for 2013/14 in     2013/14 in the
                                 counterfactual scenario      the counterfactual         counterfactual scenario

   Impact level at which         50% of 2013/14 impact        50% of 2013/14 impact      70% of 2013/14 impact
   reduction stabilises          level held for eight years   level held for eight       level held for eight years
                                 and then impacts             years and then impacts     and then impacts increase
                                 increase again at 5% per     increase again at 5% per   again at 10% per annum
                                 annum thereafter to a        annum thereafter to a      thereafter to a maximum of
                                 maximum of 150% of           maximum of 150% of         150% of 2008/09 impact
                                 2008/09 impact levels        2008/09 impact levels      levels

18                                                                                       Invasive Animals CRC
These strains were genetically compared to the Czech        inclusion of two new promising strains that were
351 strain to ensure that the most successful and most      identified late 2012) and it is expected that
genetically distinct strain/s would be selected for         recommendations for the release of additional strains
further testing. Five strains were selected for further     will be made based on the results of this study. As
testing, including a prototype strain, several antigenic    different properties of a putative new strain may be
variants and a highly virulent recent Australian field      required to overcome each of the three problems listed
isolate.                                                    above, it is feasible that different strains may be
                                                            recommended to combat the different issues
The project is premised on the following facts:
                                                            underlying RHDV-mediated biocontrol.
     Australia has only one RHDV strain (Czech 351 or
     CZ351),                                                Overcoming immunity to existing RHDV strains
     In some areas Australian rabbits are beginning to      A rabbit that survives infection with RHDV will be
     develop genetic resistance to the original Czech       immune to lethal RHD for the rest of its life. Re-
     strain                                                 infection can occur, but will only result in a boost in
     Australia’s one      RHD    strain has     limited     immunity. Virtually every rabbit population on the
     effectiveness in cooler, wetter environments, that     Australian continent has been exposed to RHDV at some
     coincide with prime agricultural regions and many      stage since its release, and in most populations natural
     threatened ecological communities and species,         outbreaks occur regularly, albeit with varying
     due to presence of RCV-A1                              frequency. Rabbit kittens generally do not die from
                                                            RHDV until they are 3–4 weeks old; thereafter they
     In Europe, a greater variety of RHDV strains is
     circulating. European wild rabbit numbers have         become gradually more susceptible to infection and
     been suppressed for much longer than in Australia      less likely to survive viral challenge until 12 weeks of
     despite attempts to aid their recovery, and similar    age, and if first infected beyond that age most rabbits
     influences on RHD impact such as genetic               will die (Cooke 2002; Robinson et al. 2002). Young
     resistance to infection and the presence of non-       rabbits that become infected but do not die will
     pathogenic viruses.                                    develop antibodies to RHDV that will make them
The European experience, in particular, shows that          immune for the rest of their life, and these rabbits are
additional variants of RHDV and new sub-strains like        likely to be recruited into the immune breeding
RHDVa are likely to compete better against the pre-         population. Maternal antibodies from immune female
existing RCV-A1 recently isolated in Australia. RCV-A1      rabbits are passed on to their offspring and may
is almost certainly the cause of limited effectiveness of   prevent infection. These younger rabbits in turn can
Czech 351 in cooler wetter parts of Australia. In           receive their first RHDV infection at a later age, closer
contrast, in Europe new variants of RHDV are                to when they become susceptible to lethal infection
continuing to suppress wild rabbit populations in           (Robinson et al. 2002). In some situations, maternal
wetter, cooler regions, despite the presence of benign      antibodies my not prevent infection but may slow the
viruses similar to RCV-A1. In addition, the resistance to   course of disease in the infected individuals and reduce
infection due to altered carbohydrate structures on the     mortality rates (Cooke 2002).
mucosal surfaces of some European rabbit populations        Depending on regional rainfall patterns, most rabbit
can be overcome by different virus variants that bind       kittens are born in late winter/spring. Consequently,
slightly different carbohydrate receptor structures         RHD epizootics are most effective in the autumn/early
(Nystrom et al. 2011)                                       winter period when susceptible sub-adult rabbits are
The selected strains are currently being evaluated for      challenged, before the breeding season, when young
their competitive advantage, their ability to overcome      rabbits are present (Cooke 2003, Kerr and Strive 2012).
both genetic resistance and acquired immunity and           However, spring is the usual time of RHD outbreaks in
their effectiveness against animals previously infected     many populations across the country, as this is the time
with the benign virus RCV-A1. The results of these          when young rabbits reach the susceptible age and
trials should be reported by December 2013 (after the       enough individuals are present to carry an epidemic. At

Benefits of Rabbit Biocontrol in Australia                                                                      19
the same time there are still enough young rabbits that    rainfall areas than it did the arid, semi-arid areas of
will survive the outbreak with resulting immunity. In      Australia (Mutze et al. 1998, Saunders et al. 1999,
addition, areas with more homogenous rainfall patterns     Henzell et al. 2002). This patchy efficacy of RHD has
allow low level rabbit breeding throughout the year        been attributed to the partial cross-protection of RCV-
and thus constant availability of unsusceptible rabbits,   A1, a benign calicivirus which prevents infection with
further diminishing the impact of RHD outbreaks in         the pathogenic RHDV (Nagesha et al. 2000, Cooke et
these areas.                                               al. 2002, Robinson et al. 2002). This virus was recently
                                                           identified and confirmed to provide partial and
The RHD-Boost project is addressing this problem by
                                                           transient protection to lethal RHDV infection (Strive et
investigating naturally occurring antigenic variants of
                                                           al. 2009, Strive et al. 2010, Strive et al. 2013). This
RHDV, also referred to as RHDVa. There is evidence
                                                           virus is most prevalent in the cool/temperate-wet
that RHDVa can partially overcome vaccination with
                                                           regions of Australia and probably arrived in Australia
the prototype virus (Schirrmeier et al. 1999), and there
                                                           with the first wild rabbits in 1859 (Jahnke et al. 2010.
is also evidence that RHDVa strains are replacing the
                                                           Recent work (Liu et al., in preparation) has shown that
prototype strain in wild rabbit populations in Europe.
                                                           the distribution of RCV-A1 is closely linked to those
Furthermore, a recent report from China describes a
                                                           cool/temperate-wet       areas    where     RHDV     has
further variant (‘RHDVb’) that can partially overcome
                                                           traditionally had limited or patchy impact, and that
immunity to RHDVa (Wang et al. 2012), indicating that
                                                           encompass both Australia’s high production areas and
antigenic differences can be advantageous in the field.
                                                           the areas where rabbits cause serious ecological
Interfering endemic non-pathogenic caliciviruses –         damage (Figure 7).
When RHDV was first released in Australia it noticeably
caused lower rabbit mortality in the temperate, high

                                                                               Figure 7: Distribution of the
                                                                               benign endemic calicivirus RCV-
                                                                               A1 in Australia. Red dots
                                                                               indicate current and historical
                                                                               sites that have tested positive
                                                                               for RCV-A1. (Commonwealth of
                                                                               Australia 2008, RCV-A1 data
                                                                               from Liu et al., in preparation).

20                                                                                  Invasive Animals CRC
Overcoming genetic resistance in wild rabbits              MV may be of considerable benefit to rabbit
                                                           conservation efforts in Europe. Australia is in the
A recently published study links the initiation of RHD
                                                           fortunate position of having only one variant of RHDV,
resistance in Australia’s wild rabbits to low dose
                                                           unlike Europe, and as such, can evaluate the impact of
infection with the originally released strain. These
                                                           additional strains on rabbit populations.
genetically resistant populations were mainly located
in the more arid areas of Australia (Elsworth et al.       Measuring impact
2012). The exact mechanisms for this resistance are
unknown at this stage. However, one of the genetically     The release of any new strains will not have the same
resistant populations identified in the Hattah region of   impact as the initial release of RHDV had on completely
Victoria (Nystrom et al. 2011) has been shown to have      naïve populations in the 1990s, and the effects will be
a higher proportion of rabbits that lack the               more subtle and difficult to measure. As such, the RHD-
carbohydrate structures on the mucosal surfaces that       Boost Release and Performance Measurement project
are likely to facilitate the uptake of RHDV. Notably,      will require a number of sites to be intensively
despite this reported genetic resistance to infection,     monitored, both before and after the release of any
serological studies at this site reveal a very high        new RHDV strain, to accurately assess its impact. Both
prevalence of RHDV antibodies in the population            treatment and control sites will need to be established
(Tarnya Cox, unpublished).                                 across a range of climate and habitat types. Specific
                                                           diagnostic tests will need to be implemented to
RHD-Boost Release and Performance Measurement              determine which strain is present during an outbreak,
                                                           and multiple samples will need to be collected from
The RHD-Boost Release and Performance Measurement
                                                           multiple sites before the true impact of any new
project will address fundamental questions about the
                                                           strains can be known.
release of a new strain of RHDV into the Australian
rabbit population. What impacts do these new strains       While the effects can be expected to be more subtle
have on rabbits? What do those impacts mean for the        than the initial release of RHDV into a naïve
Australian environment?     How will native wildlife       population, the aim of the project is to slow down the
recover? Can these new strains provide a respite for       recovery of rabbit populations by maintaining the
the recovery of threatened or endangered species?          significant benefits that RHDV has provided over the
Will the new strain/s reduce rabbit numbers to a level     last 15 years. In addition, introducing a new strain of
to allow native vegetation regeneration? What impact       RHDV may also increase the genetic diversity of the
will this have on carbon sequestration? Answers to         virus and therefore provide opportunity for the virus to
these questions are of vital importance if we are to       more quickly adapt to any acquired immunity or
continue to use strains of RHDV as biocontrol agents       genetic resistance developed by the rabbit. This
into the future.                                           project will also provide a framework for investigation
                                                           and performance management of releases of any new
This research also has far reaching consequences.
                                                           biocontrol agents for rabbits and/or other vertebrate
Populations of rabbits declined greatly following the
                                                           pest species in Australia.
spread of RHDV across their original home range on the
Iberian Peninsula.     The rabbit is listed as near        Integrating conventional control
threatened in its natural range by the World
Conservation Union (IUCN) and vulnerable in Spain. The     Improving our understanding of virus interactions in the
decline in populations of rabbits on the Iberian           field will better inform current conventional control
Peninsula have impacted on populations of their highly     practices. Improved understanding of the impact of
dependent predators the Iberian lynx (Lynx pardinus,       additional virus strains on rabbit populations under a
critically endangered) (Ward 2004) and the Spanish         variety of landscape and climatic conditions will lead
Imperial    eagle   (Aquila    adalberti,   vulnerable)    to the improved application of conventional control
(Margalida et al. 2007). Research into the interaction     techniques to maximise the impact of biocontrol
and impact of additional strains of RHDV on rabbits, as    agents.    The National Rabbit Facilitator position
well as the interaction of multiple RHDV variants and      (established through the IA CRC and due to start in

Benefits of Rabbit Biocontrol in Australia                                                                    21
mid-2013) will draw on the information obtained from          previously released strain of RHDV, it is assumed that it
the RHD-Boost Release and Performance Measurement             will then spread naturally throughout the rabbits
project to ensure best practice management is applied         range, augmented by further intentional releases at
across the landscape. Conventional control needs to           strategic sites. As such, usage of this output is assumed
be applied in conjunction with the use of biocontrol          to be 100% provided it will occur over the rabbit's
agents for maximum impact. The National Rabbit                entire range. Usage, however, should not be confused
Facilitator will encourage this combination of                with effectiveness as this will vary between climatic
conventional control and biocontrol techniques, as well       regions (Agtrans Research 2009). The release of new
as advice on the appropriate variant of RHDV for              RHDV strains has the potential to suppress rabbit
release, based on information gathered during the             populations over 5.33 million square kilometres (entire
RHD-Boost Roll-out.                                           rabbit range) (West 2008).

Impact of RHD-Boost                                           Risk factors for not achieving some of the outputs and
                                                              outcomes have been included in the estimates made of
The probability of impact of the RHD-Boost project            the expected benefits.        Results show that, for a
given usage is 80%. The expected impacts of the               discount rate of 5%, the present value of the
usages of the outputs produced by the investment are:         anticipated R&D investment of $2.6 million (2008/09
     Observed spread of the released strains so that          terms) will provide a large return on investment.
     they are endemic throughout Australia within             Investment criteria are a net present value of over $1.4
     three years.                                             billion over a fifteen year period and a net present
     The virus is effective in killing rabbits in the field   value of over $1.8 billion if a 30 year planning period is
     and rabbit numbers decrease in most regions of           assumed. For the fifteen year period, the industry
     Australia over the first three year period. This         benefits dominate at 60% of the total benefits, with
     likely impact is supported by recent experience in       the carbon sequestration benefits contributing 40%
     France (Le Gall-Recule et al. 2011)                      based on the government carbon price of $20 per
     Costs of rabbit control using traditional methods        tonne. The benefit cost ratios are 563 to 1 and 708 to 1
     fall.                                                    for each of the 15 and 30 year periods. The internal
                                                              rate of return is 217% for the 15 year period and similar
     The new strains are effective in those areas where
                                                              for the 30 year period (Agtrans Research 2009).
     the strain introduced in 1995 was ineffective and
     antibodies produced from RCV-A1 are no longer            The biodiversity benefits include the regeneration of
     effective in protecting rabbits from RHDV.               five endangered ecological communities and the
     Individual commercial grazing animal productivity        regeneration of the 75 listed critically endangered and
     is observed to increase as a result of the release       endangered plant species (excluding off-shore islands)
     of the new strains.                                      listed in the rabbit Threat Abatement Plan.
     Greater shrub and tree natural establishment
     (including    some       threatened      ecological
                                                              RHD Resistance Model
     communities) is observed due to the decline in           Collection and genetic sequencing of RHDV recovered
     rabbit numbers and there is an observed                  from rabbits around Australia has shown that since the
     secondary biodiversity impact via reduced rabbit         initial introduction and spread of the Czech351 strain
     predators such as foxes and/or wild cats.
                                                              into Australia, the virus has undergone a process of
The increase in standing vegetation from improved             gradual genetic changes. Three distinct genetic groups,
regeneration acts as a carbon sink.                           each containing a range of genetically distinct variants,
                                                              have evolved in separate but overlapping regions of the
Benefits of RHD-Boost                                         country (Kovaliski et al. 2011). Three RHDV variants,
The RHD Boost output will initially be released in            collected from outbreaks in different years at
strategic sites throughout the rabbits range using the IA     Turretfield in South Australia, have been shown to
CRC’s freeze-dried RHDV bait technology. Like the             cause different mortality rates in wild-type rabbits,

22                                                                                     Invasive Animals CRC
with associated different times to death (Elsworth et           strains that will hopefully extend RHDV-derived
al. in prep.). Of these, the most recent viruses were           benefits for several more years, co-evolution of host
the most lethal and all were more lethal than the               and virus is likely to again lead to genetic resistance
original Czech strain. Taken together with the evidence         development. Similarly, widespread immunity will
of emerging genetic resistance to infection in                  develop once the new strains have become endemic in
Australian rabbit populations (Elsworth et al. 2012),           rabbit populations. In contrast, the RHD Accelerator
this indicates that both gentic resistance in rabbits and       project aims at developing a platform technology that
RHDV virulence are co-evolving in a complex, ongoing            will allow the ongoing selection of tailored RHDV
manner. We need to understand how these processes               strains able to better overcome immunity to existing
are interacting to aid selection of appropriate RHD             field strains of RHDV and RCV-A1, by exploiting the
Boost variants for release. The RHD resistance project          principles of natural selection.
will use results from laboratory challenge studies and
field epidemiology to develop a statistical model of            Replicating natural selection
RHD resistance that can be used to project the likely           RNA viruses such as RHDV have naturally very high
benefit of RHD Boost candidates with different                  mutation rates. During replication, virus genes are not
epidemiological characteristics.                                replicated exactly, producing a mixture of progeny
                                                                viruses that are all slightly different (Domingo et al.
RHD Accelerator                                                 2001). Some of these viruses will have altered surface
                                                                structures that may not be neutralised by antibodies
Objective and rationale
                                                                specific to the original strain. These variants are
The RHDV accelerator strategy takes the RHDV Boost              slowly selected for in natural infections, as RHDV often
project to the next level. While RHD-Boost can be               kills the animals too quickly for these selection
expected to deliver one or several additional virus             processes to occur. The Accelerator project aims at

  Table 3: Summary of the economic, environmental and social benefits from the RHD Accelerator Investment
  (Agtrans Research 2011).

  Economic                              Environmental                          Social

      Higher level of grazing               Increased regeneration of native       Continuance of a more humane
      productivity translated into          vegetation and habitats, and in        method for limiting rabbit
      additional farm profits in each       the long term improved                 numbers and reduced
      of the three rainfall zones           biodiversity of fauna and flora        externalities from poisoning
      Reduced costs of rabbit               Increase in standing biomass via       control methods
      control costs by governments          regeneration leading to                Stronger rural communities from
      and landholders                       absorption of carbon dioxide.          ‘drought proofing’ and enhancing
      Reduced damage to crops               Greater ability to capitalise on       the continuing viability of some
                                            summer rains as native grasses         pastoral properties.
                                            re-establish                           Improved landscape amenities
                                            Improved biodiversity from
                                            reduced numbers of feral cats
                                            and foxes
                                            A possible cost in the potential
                                            increase in greenhouse gas
                                            emissions if ruminant livestock
                                            numbers increase
                                            Reduced soil erosion and land

Benefits of Rabbit Biocontrol in Australia                                                                         23
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