- 3.1 Assessment of the likely success of RCD virus in achieving the stated pastoral/environmental goal, with and without conventional control.
- 3.2 Assessment of the ability of RCD virus to maintain the stated pastoral/environmental goal over time.
- 3.3 Humaneness.
3. The effectiveness and suitability of RCD virus as a biocontrol agent in New Zealand
Ideally, for a virus to be a candidate for biological control of rabbits the following criteria should be met:
- it is host-specific,
- it has a high morbidity and a case fatality rate of more than 90%
- it should exhibit long term stability in terms of host specificity and virulence,
- it has a very effective means of natural transmission,
- it should be humane,
- there must be means to protect valuable rabbits,
- the virus is well characterised and can be grown in vitro.
Biological control agents are usually released into the environment where they have the potential to spread. Usually their activity cannot be controlled and neither can they be retrieved. A few biological control agents can be used as biocides where their effect is short term, their ability to spread is restricted and their effects are localised. A true biocide kills its target species after exposure and there is no secondary spread of the agent. It behaves like a toxin.
3.1 Assessment of the likely success of RCD virus in achieving the stated pastoral/environmental goal, with and without conventional control.
| Pastoral and Environmental Goals |
| The goal of RCD release in New Zealand is not immediately clear from the Application. The Application states: |
| "The goal of the release of RCD in New Zealand is equivocal because the nature and extent of the rabbit problem vary greatly, and the spread and persistence of RCD are uncertain." |
| It goes on to say what their minimum goal is: |
| "It is hoped that the long term suppression of rabbit populations will be such that widespread poisoning is no longer necessary." |
| The RCD Applicant Group (Response to review reports, part two) emphasise that: | |
| "the decision maker must evaluate all the potential benefits of RCD, well beyond the minimum goal for the release programme." | |
Submitters in support of RCD comment that the broad goals of the programme are to provide long-term benefits to tussock grasslands and sustainable land management, with flow on benefits to farm families, the farming community, the rural economy, and national society through improved exports.
They believe that RCD would break the cycle of increasing expenditure and diminishing control. They argue that with biocontrol, secondary control measures would more affordable, along with fertiliser, weed control and debt reduction.
A number of objectives can be identified from the submitters in support of an introduction. These include:
- to use the new tool along with a number of existing control measures;
- to reduce the use of poisons;
- to lessen land erosion and degradation;
- to encourage revegetation and gain soil and water benefits;
- to engage in better planning and address sustainable land use issues;
- to allow farmers to concentrate on the positive aspects of farming and profitability;
- to help control the spread of bovine Tb.
There is also a claim that RCD provides the only opportunity for effective widespread control of whole farms and districts.
| A number of submitters recognised that biocontrol was not the complete solution to the rabbit problem and advocated its use with other methods of rabbit control. While recognising its role in a package of control methods, they usually did not discuss how it would be integrated with conventional controls. One supporter (399), however, did clearly express what an integrated approach would require: | |
| "The introduction of rabbit calicivirus will not solve the problem, but if the opportunity is taken to introduce it in a carefully planned and strategic manner, and a committed and concerted effort is made to follow up with appropriate control techniques, I am convinced that we could make a dramatic and long term impact on the rabbit." | |
Submitters have questioned whether a relatively localised regional problem, where only a small percentage of land area is highly susceptible to rabbits, justifies the introduction of a virus which has potentially significant national costs in ecological terms.
Those submitters opposing the introduction of the virus saw it as a "quick fix", one that would bring temporary financial benefit to a small group. They also are concerned that any reduction in rabbit numbers should be effective in the longer term. Pressure, they say, has to be kept on the rabbits. Indeed, they point out that as a control tool it may have only a relatively short "life" and that land management changes would also need to be made.
| The Ministry for the Environment believes that there is a need for a clear statement of the goals of an RCD virus release, together with the need for a comprehensive release strategy that would enable assessment of the ability of RCD to maintain the stated environmental/pastoral goals over time. This release strategy should also adopt sustainable land management practices, especially in the degraded areas of the South Island high country. Ministry for the Environment believes that a strategy might include: | |
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The Ministry for the Environment believe that this is important because, without a comprehensive release strategy there is a risk that RCD will be seen as a "quick fix" option, rather than part of an ongoing and integrated rabbit and land management strategy. Accordingly, they recommended that the applicants, who include the regional councils of the most rabbit prone areas, take up their responsibilities as the authorities responsible for RPMS by providing a comprehensive RCD management plan.
It is acknowledged by supporters of RCD that sustainability in the high country has attracted wide public interest and there is a need to move to more sustainable and integrated management systems. They see that effective land management is dependent on effective rabbit management. For NZ to deliver on sustainable land management, for farming, conservation and recreation lands, new methods of managing this pest have to be found.
| Both opponents and supporters agree on the long term benefits of sustainable land management for the environment and society. It is suggested that a long-term national land management strategy should therefore be developed under the Resource Management Act (1991), reinforced by education and if necessary regulation. One submitter (697) makes the point: | |
| "I think that these long-term considerations of the sustainable land use are the most important aspects of this whole debate and would like to see them discussed more fully and prominently." | |
| The South Island High Country Committee of Federated Farmers of New Zealand (555) acknowledge that sustainability in the high country has attracted wide public interest and there is a need to move to more sustainable and integrated management systems. They see that: | |
| "the two key issues affecting sustainability in the high country currently are rabbit invasion and hieracium invasion." | |
| "RCD and biological controls for hieracium, along with the passage of the proposed Crown Pastoral Lands Bill offer the biggest steps forward for the sustainable management of the high country" | |
| "Thus we believe firmly that RCD is just one part of an integrated package leading to improved management of the high country environment." | |
Likely success in achieving pastoral and environmental goals
| The Application states that: | |
| "until RCD virus arrives in New Zealand, its likely transmission, persistence and impact on feral and domestic rabbits can only be based on limited Australian and European data and field experience. On the assumption that all New Zealand feral rabbits are susceptible RCD virus can be expected to: | |
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| In addition it is expected that it will: | |
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The success or otherwise of RCD in achieving the assumed goals is dependent first of all upon the likely behaviour of RCD virus in New Zealand. As noted in the analysis of submissions the main areas of concern are:
- there is uncertainty surrounding the method by which RCD is transmitted,
- no vector for RCD has been established,
- there is uncertainty about the persistence and stability of the virus, its frequency, pattern and season of future recurrence in the New Zealand environment.
European observations
The disease, RCD, in the Northern Hemisphere is known as rabbit haemorrhagic disease and in Europe it is widespread. In stark contrast to Australia and New Zealand the status of rabbits in much of Europe is that of a valued game animal rather than pest. Rabbits are released each year for hunting in several countries. In Spain the rabbit is the most important game species and has never been considered a pest in the way it is in France. Rabbit haemorrhagic disease in Europe was and is primarily a disease of domesticated rabbits where losses have been devastating. While information on the disease in wild populations is reasonably well documented for Spain it is poorly documented for every where else.
Systematic studies of rabbits have been made in Dônana Park in Spain for many years and when RCD arrived it was one place where the impact could be objectively assessed. RCD appeared in 1988 and initial outbreaks were reported to have killed 65-80% of wild rabbit populations. The disease now appears to be more patchy in distribution and generally occurs in the winter. It is estimated that the wild rabbit population is slightly less than half its previous size (Cooke, 1995). There is some evidence for a ‘two year cycle’ of the disease in some local populations. High mortalities occur locally, but over the whole country only about half the rabbit population is affected in any one year (Ross and Trout, 1993). Recent reports show that the mortality rate in affected wild rabbits is 90%, the same as that initially reported. These results need to be interpreted with caution in respect to the potential effect in New Zealand. Myxomatosis occurs in Spain and rabbit population densities are generally much lower than here. Predator pressure is higher in Spain. The higher temperatures and drier climate in Spain may affect the survival of the virus and hence its rate of transmission. It must be remembered that the Spanish value their feral rabbits and exert no control measures against them.
In the United Kingdom RCD was first reported in two rabbitries housing show rabbits in April, 1992 (Fuller, et al. 1993). Infection was introduced to the second rabbitry by the transfer of animals. The mortality was 15% and 71% of the age susceptible rabbits on the respective properties. The source of infection for the early outbreaks in the UK was not determined and the disease has subsequently been reported widely, especially in south England. Trout believes that birds are the only reasonable explanation for the rapid spread of the virus across great distances while Chasey considers that the introduction of the disease to the UK could have been associated with the discarding of contaminated material by vehicles leaving the Channel ferries.
It is noteworthy that the first confirmed deaths in feral rabbits in the UK were not made until 1994. Chasey and others from the Central Veterinary Laboratory and Central Science Laboratory in Britain reported at the European Society for Veterinary Virology, Calicivirus Symposium in October of 1996 that antibody to RCD virus "has existed for many years in UK rabbits". Some 64% of 900 adult wild rabbit sera showed protective level of antibody before the disease was reported in the UK. This was confirmed again in 1995 when sera from 389 feral rabbits taken from 20 sites in the United Kingdom showed 75% to have antibodies to RCD. This is broadly consistent with the results of sera taken earlier and with other reports of naturally occurring antibody in Europe (Chasey and Trout). See section 7.0 for discussion on the non-pathogenic strain.
Australian observations
RCD virus was originally tested for safety and efficacy in an evaluation programme within the high security facilities at the CSIRO-AAHL in Victoria. In April, 1995, as part of this programme a series of field trials were commenced under quarantine conditions on Wardang Island, 4 km from the Australian coast. Attempts were being made to transfer RCD from infected rabbits to cohorts within double fenced pens. Sentinel rabbits outside the pens became infected, and on 12 October, 1995 rabbits on the mainland at Point Pearce were shown to have RCD. Fourteen days later, RCD was confirmed to have spread to a wide area within and around the Flinders ranges of South Australia near the towns of Yunta and Blinman and extending in a north easterly direction over an area estimated at 7,500 km2. Some of this spread (over a distance of more than 300 km) may have occurred earlier than the time of detection, possibly at the time of the Point Pearce outbreak. There were high densities of rabbits in the area, which historically has high rabbit numbers. It had also been a good season for grass growth and good rains had fallen. All age classes of rabbits were present. Investigators found the disease to be active and spreading quickly. Within affected areas the disease was patchy with mortality rates possibly greater than 80% (Newsome and Mutze, 1995). At one study site within the Flinders range numbers of rabbits were estimated to be 50 per hectare prior to the arrival of RCD. The consequent mortality rate was approximately 95%. (A second outbreak occurred approximately 10 months later when the density was 1-2 rabbits per hectare. A similar mortality rate was also recorded at that time.)
There is some evidence that insects assisted by winds were responsible for the spread of the disease from Wardang Island (Wardhaugh and Rochester, 1996).
However, it was not until RCD virus was approved as an ‘agent organism’ and the rabbit a ‘target organism’ as per the requirements of the Biological Control Act 1984 in September, 1996, that it became legally available for distribution in Australia for rabbit control.
The virus, possibly with the assistance of people, has now spread throughout all states and territories of Australia including Tasmania. It now extends over about 70% of the rabbits range. Data of rabbit numbers pre and post-RCD are limited and therefore the impact has been based on crude estimates of rabbit numbers. One feature that has emerged is that the impact on rabbits is variable within catchments. In some places high mortalities are evident over a large area while in other places mortalities have been localised to small areas.
Australia has established a two year National RCD Monitoring and Surveillance Programme based on the following:
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| Initial findings from the Report to RCD Management Group, April 1997, show that: | |
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Possible reasons for the variable impact of RCD on rabbit populations are:
- the presence of non-susceptible, young rabbits in the population when RCD arrived;
- lack of spread of the virus from inoculated rabbits to other rabbits, due to lack of vectors;
- rabbit breeding and recruitment exceeding mortality due to RCD, resulting in replacement or a net increase in the population;
- immunity of some rabbits due to a previous, undetected outbreak of RCD;
- climatic factors;
- other factors, yet unknown.
Impact on the environment in Australia
Early indications are that there may be a decline in predator numbers of foxes and feral cats. Some predators are changing their diet to include more insects and fruits. It is too early to detect any significant changes in native fauna and vegetation, especially as other factors such as drought and rain have significant effects.
| Implications for New Zealand | |
| The Application itself raises doubts about the ability of RCD to achieve the goals of an introduction: | |
| ".... until the rabbit calicivirus arrives in New Zealand it effects and persistence cannot be accurately predicted." | |
As noted above, in the Australian report, one feature of the disease is its variable effect. The lack of information about the reasons for the variable effect of RCD makes it extremely difficult to assess its potential efficacy as a biocontrol agent for New Zealand. Modeling by Barlow (1996) underscores that we know very little about how effective it would be in New Zealand. Plausible scenarios range from prolonged suppression of rabbits without intervention, to an instantaneous but short-lived knockdown without persistence of the disease.
| The Ministry of Research, Science and Technology in their submission (478), prepared by Bureau of Resource Sciences, notes that: | |
| "models of the impact of RCD in New Zealand and Australia did not show RCD persisting". | |
| The report then states: | |
| "It is not possible to be certain of the behaviour of RCD in New Zealand because many of the epidemiological factors are unknown. RCD might become endemic, or alternatively it might be used as a biocide. This would not be a matter of choice but would depend on the behaviour of RCD under New Zealand conditions." | |
| and | "Since the persistence of rabbit calicivirus and the speed of development of resistance in rabbits and attenuation of [RCD] are unknown, predicting the long-term effect of RCD release is difficult." |
The epidemiological components which might explain how the virus is spread have not been adequately determined, although in Australia, bush flies and mosquitoes are currently suggested as important mechanical vectors. The intentional and unintentional spread by people also contributes to the spread of virus. The questions of vectors and survival of the virus outside of the rabbit in varying local and seasonal environments and in/on any carrier animals are not resolved for Australia and remain open for the New Zealand environment. See also section 7.4.
In the absence of more specific information on vectors from Australia it seems reasonable to take note that the range, variety and number of potential vectors in New Zealand is likely to be less in comparison to Australia with its much greater vertebrate and invertebrate biodiversity. This may therefore mean that spread in New Zealand would be less spectacular and transmission may be dependent on direct contact between rabbits or indirectly via the faecal-oral route.
If, following the release of rabbits injected with RCD virus (section 4.3), disease outbreaks remain localised in small areas, it is possible that oral baits loaded with the virus could be used to initiate an epidemic over a wider area. Although the Application refers to these baits as a biocide, discussions with the RCD Applicant Group confirm that it is not their intention to use the virus as if it were 1080. If there was a tendency for disease outbreaks to be localised then the virus might be used with more precision and this could reduce the risk of viral exposure to domesticated rabbits. It might also allow restriction of the virus to certain parts of the country. Virus production and field distribution costs, however, might be higher than releases via injected rabbits.
Another unknown relates to the immune status and the degree of homogeneity in the New Zealand rabbit population. Although a small sample of rabbits from this country has been shown in tests at CSIRO-AAHL to be susceptible to RCD, a possibility exists that some populations might be infected with a non-pathogenic calicivirus which confers cross-immunity to RCD. Further research is presently underway to clarify this status.
Use of RCD virus with conventional control
The Application is clear in that RCD is to be used within an integrated pest management strategy.
Although a few farmers expect RCD to remedy their problem of rabbit control the majority recognise that it has potential as another tool and, hopefully, one which is cost-effective. If RCD provides only partial or intermittent control of rabbits and less secondary control effort is applied, the economic and environmental benefits may not be realised.
Farmer submitters have made repeated assurances that they stand ready to apply follow-up controls even after RCD is released and others assure that they would use the resulting "window of opportunity" to instigate more sustainable land management practises. Several other members of the public have expressed little confidence that these measures will occur and provide the long-term sustainability and the environmental benefits promised. However,there is a legal responsibility to control rabbits and if necessary regional and district councils are obliged to take steps to enforce rabbit control by way of the legally binding RPMS. See section 4 for details of the intended programme.
There already are signs that farmers are holding off applying conventional control methods in the expectation that the release of RCD virus is imminent and will be effective.
There is uncertainty about whether the biocontrol agent, RCD, would meet the goals of the Application. This is mainly due to the lack of hard data concerning how the virus would spread, its level of persistence in the environment, its likely reservoirs and vectors, and the effects of climate and host density on the epidemiology of the disease.
In order to ensure that the benefits of an RCD virus release are maximised it would have to be used in a carefully planned and strategic manner in conjunction with integrated rabbit control techniques and land management practises. Although there has been a case made for the import of RCD virus to be conditional on the adoption of sustainable land management practises this is not tenable as there is no statutory basis for such conditions.
The possibility of using RCD virus as a true biocide has not been discussed in the Application and consequently has not been assessed in this report.
3.2 Assessment of the ability of RCD virus to maintain the stated pastoral/environmental goal over time.
| Many submitters suggested that sections of the rabbit populations would develop immunity from the virus, and that their numbers would return to previous levels. One of them (697) took this view: | |
| "RCD would become simply one among many factors that influence rabbit numbers from time to time, and the populations will still tend to be larger in 'rabbit prone' areas." | |
| There is no evidence at this time that the RCD virus has lost its virulence, but it is likely that this will occur (see section 7 - mutation). | |
| "The presence of an acutely fatal infectious agent places extreme adaptive pressure on the target host species. The consequence of this is that over time the host species will adapt to resist infection, through genetic selection and possibly enhanced protective immunity. At the same time the virus may adapt (mutate) to produce variants which cause sublethal or latent infection. Whereas the acutely fatal nature of RCD has appeal for its use as a biocontrol agent, it also amplifies the selective pressures on both the host and pathogen, to adapt to a state of equilibrium. The high reproductive rate of the rabbit means that emergence of resistance traits could occur within a relatively short period (5-10 years) following release of virus." (711) | |
Very little certainty can be attached to the ability of RCD virus to maintain any stated pastoral and environment goals over time in NZ since the persistence of the virus, the speed of development of resistance in rabbits and loss of virulence of rabbit calicivirus in an epidemic are unknown.
3.3 Humaneness.
One point of view expressed commonly in the public submissions is that any method which implements large scale culling of the European rabbit is unacceptable. The appealing appearance of rabbits has considerable impact on the overall public perception of them.
| However, in the absence of natural predators in New Zealand the need to control rabbits is inescapable. Farmers argue that the image of ‘cuddly’ rabbits has to be offset by the need to deal with an urgent farm problem. | |
| "We acknowledge the concern for the associated suffering to the rabbit population. Farming communities have a close affiliation with their animals, and farmers generally have a very responsible attitude to inflicting pain on any animal." (456) | |
| The High Country Trustees (279) claim that: | |
| "when the subject is looked at objectively there is a far greater aggregate of suffering under the present regime of often-high rabbit numbers, followed by huge death rates from starvation, predation, shooting, poisoning etc. than there ever will be with lower levels under a RCD/conventional-tool mix." | |
Because of the great difficulty of objectively determining whether or not an animal is in pain the usual approach is anthropomorphic whereby I use my own human experience to project myself into a similar situation.
The period from infection with RCD virus to death is very short in comparison to that which is characteristic of many other infectious diseases. This is a very desirable feature from the point of view of humaneness. Reports on the clinical/behavioural reactions of rabbits affected and dying from RCD do not lead me to believe that the illness and death of rabbits from RCD is particularly inhumane.
A pathological feature of RCD is widespread blood clot formation in small blood vessels (disseminated intravascular coagulation (DIC)). Although any illness in human beings or animals has unpleasant features Lektos are not aware that DIC per se is a particularly painful condition in human beings and this may also be true for rabbits.
There was consensus among submitters that RCD is relatively more humane than myxomatosis, but divergent opinion about its relative acceptability compared to poisoning and/or shooting. Given the range of traumatic consequences following shooting of rabbits it is reasonable to suggest that shooting would be far less humane that those arising from RCD but this view was not shared by some submitters.
If RCD were to be released or were to spread to populations during the time that young rabbits were in their burrows or breeding stops, then the resistance of the young whose mother was killed by the disease may lead them to die of starvation. This is the most inhumane consequence of RCD introduction.
| The Royal New Zealand Society for Protection of Cruelty to Animals (262) requests that: | |
| "the release of RCD should be co-ordinated to be simultaneous throughout New Zealand at a time when it is expected that the least number of suckling kits will be left to starve to death in the burrows. | |
| We feel that timing for efficacy of the virus should not take precedence over timing for least suffering for the animals." | |
The death of suckling young from starvation subsequent to the death of does is a feature of any system of rabbit control which kills does in the breeding season. Deaths of suckling young associated with rabbit control should however be seen in the context of reported high "natural" mortality in young rabbits e.g 90% mortality to 6 months of age in rabbits born in the Wairarapa between May and November and even higher mortality among those born at other times of the year. A large proportion of such mortality is likely to be due to the activity of predators which is of course associated with considerable pain and stress (Lektos).
Ideally, the virus should not be released at a time when suckling kits could be left to starve to death in the burrows. However, in a natural epidemic of RCD and in the current poison programme mortalities can occur at any time of the year.
The absence of literature detailing symptoms of unacceptable suffering suggest that RCD is no more inhumane than any other means of control.
Conclusion
The Application predicts a more positive result from an introduction of RCD than current evidence would allow me to conclude.
I am unable to predict whether RCD would be an effective and suitable biocontrol agent in New Zealand. (For further discussion see section 7.0)
The use of RCD virus as a biocide has not been assessed.
RCD virus appears as humane as other rabbit control measures in New Zealand.
Contact for Enquiries
Manager, Strategic Science Team
MAF Biosecurity New Zealand
PO Box 2526
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NEW ZEALAND
Phone: +64 4 894 0115
Fax: +64 4 894 0731
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