Rabbit Biocontrol Advisory Group
RCD - Risks and Benefits
A decision on releasing RCD requires an assessment of risks and benefits. In New Zealand any assessment will be done by the Ministry of Agriculture Regulatory Authority under the Animals Act.
This involves a careful weighing of :
- the risks associated with introducing a virus,
compared with:
- the environmental and agricultural benefits that can be gained.
Research on rabbit calicivirus has been conducted in Australia since 1990. Information has also been gathered from a number of countries where the virus has been present for over 10 years. This knowledge is critical to assessing the risk of releasing RCD in New Zealand.
Perception of risk
We make daily judgements about whether to take certain risks. Yet, our perception of the risk involved with a certain decision or action is often different to the reality. For example, we may perceive a greater risk from air travel than travelling in a car, even though the actual risks of car travel are far greater.
Our judgements about risk are affected by our perception of the benefits to be gained and the fear we feel about taking the risk. We tend to accept higher levels of risk when we perceive personal benefit to be high. These perceptions are also greatly affected by our knowledge of the risk, and the amount of control we have, or feel we have, over the decisions that result in our being exposed to the risks.
Reliable information and good communication are essential to ensure there is an informed debate on the pros and cons of introducing RCD. This debate needs to be part of a wider one about how we achieve sustainable land management in New Zealand. The ultimate objective of reducing rabbit numbers is to improve the sustainability of farming and conservation lands.
It was the need to ensure an informed debate about the way we manage rabbits in New Zealand and the control methods used that led to the formation of the Rabbit Biocontrol Advisory Group in mid-1995.
This group of 17 people was established to advise the Chief Executives of the Ministries of Agriculture, Environment, Research, Science and Technology and the Department of Conservation. Members were invited to be part of the group after wide consultation and represent the views of those concerned with conservation, animal welfare, Maori, science, agribusiness, animal health, farming, regional and central government.
Risks of releasing RCD
As with the release of any virus, the risks to be considered include:
- we have adequate information about the host range of the virus;
- risk of RCD compared to other control methods;
- the virus is likely to mutate in such a way that it is able to infect other species;
and, based on these points,
- the virus will infect or cause any threat to other animals or humans.
Information on risks of RCD
Scientific research conducted on RCD in Australia supports the knowledge and experience with RCD in other countries. This shows that rabbit calicivirus, based on species tested to date:
- species-specific, only infecting European rabbits;
- not been shown to have harmful effects on human health, despite humans being exposed in most of the 40 countries that the virus now infests;
- remained stable - that is, exhibiting no changes that would be likely to result in an infection of another species - since it was first discovered over 10 years ago;
However, there is evidence that RCD can produce antibodies in some species (e.g. mice and kiwis, and possibly others). This does not indicate infection or susceptibility of the species, but does indicate a need to know why some species respond when most tested to date do not.
Other caliciviruses are not so species-specific. An example is the San Miguel sea-lion virus, which has the ability to infect a wide range of animals, including species as varied as fish, seals and pigs. These characteristics have led some scientists to suggest that the rabbit calicivirus may, sometime in the future, also infect other species. The possibility of that occurring, and that any infection affects an animals health, has to be assessed as part of a decision on whether or not to release.
Like all organisms, viruses evolve through genetic change or mutation. This change in the virus may:
- no effect;
- the virus;
- it less virulent or harmful to its host animal;
- it more virulent to the animal it infects;
- rare cases (one known), enable it to infect species that were previously not susceptible.
It is impossible to guarantee that a virus will never affect another species, but the probability of doing so appears to be extremely low. All viruses have the potential to change in ways that could represent a greater or reduced risk to humans. Those currently known to affect humans will generally continue to be the greatest risk. In relation to RCD, this risk must be weighed against the expected benefits of release and the consequences of having to continue to rely on current control methods; which, in turn, have their own risks.
Benefits of releasing RCD
There are many potential benefits of RCD accruing to the environment, private landholders, government and the general public, including present and future generations. To realise these benefits, RCD would need to be used as part of an integrated rabbit control strategy to achieve effective, long-term rabbit control.
These benefits include:
- tussock grasslands to recover from persistent rabbit grazing pressure and avoid possible desertification in some areas, assuming that livestock numbers are not significantly increased;
- soil erosion; and the associated rehabilitation costs;
- opportunities to effectively control other feral pests, i.e. predators, that will no longer have rabbits as a plentiful food source;
- success and reducing the cost of environmental programmes (e.g. tree planting);
- the costs of rabbit control on public and private land and the associated research;
- the effectiveness of conventional rabbit control methods;
- the quantity and quality of agricultural production;
- land management in some areas important for biodiversity or of high conservation value;
- to protect future land use opportunities.
Risks of continuing to rely on current control methods
Rabbits have caused periodic but serious damage to land, native vegetation, and agricultural production since the 1870s.
The environmental, production and control costs have been considerable. Since 1950,as a result of better-organised control, agricultural development and new poisons such as 1080, rabbit numbers have been dramatically reduced over much of New Zealand. The cost has, however, been high: over $600 million in mid-80s dollars.
Extensive control is still required. Some rabbit populations are now 1080 and bait-shy, reducing the control effectiveness. In many areas, another important biological control of rabbits, ferrets, have Tb and may have to be controlled to prevent spread to livestock. If so, rabbits are likely to increase again in many areas. Other methods of control are therefore likely to be needed.
Over the last 20 years several rabbit poisons have been withdrawn because of the risks posed to users or other species. Only one poison has been registered, and it, in common with current poisons, presents risks to other species.
Unless we are able to achieve more effective rabbit control, there will be major and, in some cases, irreversible changes to some ecosystems. This will reduce the viability of agricultural production and other land uses, including recreation and conservation in some areas.
This will increase the risk that ratepayers and taxpayers will once more have to fund extensive control and possibly restoration programmes.
Other future control
Research into an immunocontraceptive for rabbits is underway, but there is no guarantee of success. It will be several years before research is completed and fully assessed for field release. For New Zealand, this technology will also involve introducing an organism that has been genetically modified, the myxoma virus, and will also involve risks that will have to be carefully assessed.
Further Reading on Risk:
Risk: Analysis, Perception and Management.
Report of a Royal Society Study Group
1992
London Royal Society
Risk Society; Toward a New Modernity
Beck V. 1992
London: Sage
Perceptions of Risk
Slovic. P 1989
Science Washington
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
Contact this person
