- Introduction
- Conclusions from the Report of the Chief Veterinary Officer
- to the Decision-Maker
- 1.0 The rabbit as a pest in New Zealand
- 3.0 The effectiveness and suitability of RCD virus as a biocontrol agent.
- 4.0 The intended programme in which RCD virus is proposed to be used.
- 5.0 The effects, positive and negative, of RCD virus
- 6.0 The likely success and costs of measures to ameliorate negative impacts.
- 7.0 Characteristics of the virus and its method of production and dispersion.
- 8 .Cost and benefits of RCD virus introduction.
Report of the Chief Veterinary Officer to the
Decision-maker
on the
application to import rabbit calicivirus
into New Zealand
as a biological control agent for feral rabbits
Introduction
| On 27 June 1996, the RCD (rabbit calicivirus disease) Applicant Group lodged an application to import rabbit calicivirus (hereafter referred to as RCD virus) as a biological control for feral rabbits with the Ministry of Agriculture. The application was considered under section 21 (1) of the Animals Act, 1967, which provides: | |
| "No person shall, without the written permission of the Director-General, knowingly introduce any organism, or knowingly cause any organism to be introduced, into New Zealand." | |
MAF’s Deputy Director General, Peter O’Hara was delegated to be the decision-maker for the RCD application.
The Chief Veterinary Officer, Barry O’Neil was responsible for the consultation and assessment process.
This is the Chief Veterinary Officer’s report which is a technical assessment based on the outcome of the consultation and assessment process.
Conclusions from the Report of the Chief Veterinary Officer to the Decision-Maker
1.0 The rabbit as a pest in New Zealand
About 9% of the land area in New Zealand is classed as moderate to extremely high in rabbit proneness. Rabbits can reach high numbers on this land and cause serious ecological damage which is costly in environmental, cultural and financial terms.
While rabbits are not considered to be a problem throughout the country, to the extent which would warrant a national pest management strategy, they are seen as a problem of national importance.
It is likely that most native fauna, with few exceptions, is negatively affected by the type of habitat modification effected by rabbits. Some native fauna is even more directly affected by rabbit predators.
Rabbits have a high impact on flora via the direct defoliation of plants, modification of plant communities and destruction of the soil structure.
In addition to these ecological effects rabbits also compete with livestock for feed and damage crops and trees.
Tourism is important in the semi-arid land of the South Island and rabbits are degrading parts of the landscape in what is commonly considered to be a "national heritage" region. The preservation of our environment with its associated conservation values is of benefit to all New Zealanders.
2.0. Assessment of current control measures
| The Application conclusion of the assessment of current control measures is an accurate summary: | |
| "To counter the rabbit problem, New Zealand has made use of a range of control methods. A combination of many of these methods - notably poisoning and shooting, trapping or fumigating - has generally succeeded in lowering rabbit numbers at least temporarily, and Regional Pest Management Strategies ensure the continuation of a planned and integrated approach to control." | |
While current methods of rabbit control are effective they have a high cost in relation to the commodity prices recovered from the land. For properties with land of moderate to extreme rabbit proneness the cost of rabbit control is often greater than the financial returns that control brings. Rabbit control is therefore not financially sustainable so rabbit numbers are increasing together with the resultant degradation of the land in the worst areas.
In addition, the present reliance on the use of 1080 is a serious weakness in the current approach to pest management given the potential market risks and technical limitations associated with its widespread use.
I therefore find that there is a case for an alternative rabbit control.
3.0The effectiveness and suitability of RCD virus as a biocontrol agent.
The Application predicts a more positive result from an introduction of RCD than current evidence would allow us to conclude.
I am unable to predict whether RCD would be an effective and suitable biocontrol agent in New Zealand. 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 a 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.
The use of RCD virus as a biocide, i.e. where it is used like 1080, has not been assessed.
RCD virus appears as humane as other rabbit control measures in New Zealand.
4.0 The intended programme in which RCD virus is proposed to be used.
The legal basis for regional councils having exclusive use of RCD virus in New Zealand is uncertain based on the RCD Applicant Group’s statement that regional pest management strategies are not appropriate for regulating the release programme. Until this issue is clarified it is doubtful that the potential benefits of RCD can be realised.
Resources have not been identified for all aspects of the biocontrol programme. Ideally, there should be an agreement among parties as to who would be responsible for providing each of these resources.
5.0 The effects, positive and negative, of RCD virus
The Ministry of Health consider that the virus poses a low risk to human health but have some reservations because there is little known about the behaviour of the virus. However, the virus is widespread in more than 40 countries and no convincing evidence of human infection has been presented.
Rabbits are a direct threat to certain Maori values and are recognised as a pest. However, the potential loss of indigenous species through predator prey switching is of greater concern and because of this Maori want protection measures to be given high priority.
It is not possible to predict the indirect effects of the virus on indigenous flora and fauna because it is not known how the virus would behave in New Zealand. Two scenarios are discussed:
- cyclical epidemics with large fluctuations in rabbit numbers. Under this scenario, when rabbit numbers decline, it is anticipated that there would be an increase in predation pressure on native fauna (due to prey switching and predator guild changes). These changes in predation pressure would occur periodically in response to changes in rabbit numbers.
- rabbit abundance is permanently suppressed by RCD. Habitats would change but there are no reliable data to predict whether net predation pressure on native biota would increase or decrease. The effect is likely to vary in strength from place to place and potentially also between indigenous species.
It is likely that commercial rabbit harvesting enterprises would be possibly severely affected by an introduction of RCD virus.
The potential to export products from the biotechnology industry could be affected to some extent by the arrival in New Zealand of another virus infection such as RCD.
6.0 The likely success and costs of measures to ameliorate negative impacts.
Twenty nine threatened species at 59 sites have been presently identified by Department of Conservation as requiring protection from an increase in predation or weed competition in the event of an RCD-induced decrease in rabbit numbers. In addition there are up to ten high profile sites where protection would be required.
The mitigatory measures recommended by Department of Conservation must be considered by the decision maker. Clarification of the costs and the funding sources for mitigation need to be resolved before the RCD virus could be released.
Without doubt an introduction of RCD virus would mean that owners of valued rabbits (pets, show animals, farmed rabbits, and those used in research and industry) would face increased costs in protecting their rabbits from infection. These costs have not been quantified.
7.0 Characteristics of the virus and its method of production and dispersion.
The scientific evidence leads me to believe that a calicivirus causes the disease and that the disease risk assessment will address the purity of the inoculum.
I consider the risk of adverse mutation to be no greater or less than other RNA viruses already in New Zealand but it is not zero.
Although there is no convincing evidence of RCD infection in species other than the European rabbit, questions remain about host specificity and the possibility of subclinical infections.
There is much that is unknown in regard to the pathogenesis and epidemiology of the disease. I believe a number of key questions remain unanswered and these include:
- How is the virus transmitted from rabbit to rabbit?
- What is the most effective mode of transmission?
- What is the role of vectors in the transmission of the virus?
- What are the host factors for the spread of the disease in the rabbit population?
- What are the favourable environmental conditions for the spread of the disease in rabbit population?
- What is the relationship between host susceptibility and dose of the virus?
- Is there an interaction between the exposure of this virus and other disease agents in the rabbit population or other animal populations?
- What are the limitations of the current diagnostic procedures for the disease in the rabbit population in terms of its sensitivity and specificity (i.e. accuracy)?
- What is the potential for RCD virus to be a carrier of other viral agents?
- How does RCD virus persist in the field?
My inability to confidently answer these questions highlights my uncertainty as to how the virus would behave in New Zealand and therefore assess its potential as a biological control agent.
8. Cost and benefits of RCD virus introduction.
I consider that the major beneficiary of effective biological control of the rabbit would be New Zealand "incorporated". The primary benefit would be for the preservation of New Zealand’s ecosystem and conservation values and not to individual farming businesses.
An RCD virus introduction would also result in significant costs. Exactly who would be expected to meet these costs should be agreed before the virus was imported.
Contact for Enquiries
Manager, Strategic Science Team
MAF Biosecurity New Zealand
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0115
Fax: +64 4 894 0731
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