Introduction and Disclaimer
TopicsRCV as a biocontrol agent:
Host range of the virus:
Risk of human infection:
Probability of RCV to mutate and consequences of mutation of RCV:
The effect of introduction on New Zealand flora and fauna:
Program to release the virus:
Conclusions:
ANALYSIS OF THE IMPACT OF THE PROPOSED INTRODUCTION OF THE RCD VIRUS TO NEW ZEALAND
24 February 1997
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M.D. Salman BVMS, MPVM, PhD
Professor of Veterinary Epidemiology
Center for Veterinary Epidemiology
and Animal Disease Surveillance Systems
Colorado State University,
College of Vet. Medicine & Biomedical Sciences
Ft. Collins, CO 80523 - 1676
Wk. 970-491-7950 or 0353 fx. 970-491-2940
msalman@vagus.vth.colostate.edu
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This report is in reference to Dr. Barry O'Neil's letter dated December 23, 1996. My report was written after reviewing the following documents and literature:
1. Comments from the peer reviewers - first round
2. Comments from the peer reviewers - second round
3. Comments from the public submissions
4. Taylor Baines and Associates Report- Analysis of the public submission comments
5. The original IIA document with its appendices
I have considered the Terms of the References for my task. My comments and suggestions in this report are solely my opinion and expertise. They are, on some occasions, reflections on the comments and facts that I have identified from the above documents and literature. I would like, however, to express the following facts about my opinion and expertise:
1. I do not have any personal interest in the issue of the introduction of the RCD.
2. I do not have any personal interest in the promotion of any of the parties who are involved in this issue.
3. I have not been in New Zealand and I have not been exposed to several of the issues that are related to the introduction of the virus such as the politics, agricultural policies, Maori culture, and livestock management.
4. My expertise with this virus was obtained directly from a literature review of several articles, text books, and veterinary training. I have not conducted research on this virus.
5. My expertise is predominately in the field of animal disease control programs and strategies as well as national animal disease control and monitoring systems. Analytical epidemiology and infectious diseases are my major field of interest and expertise.
This report is to assist in the decision making process and does not attempt to suggest a final decision. It is organized by the topics listed in Dr. O'Neil's letter with reference to the matters to be considered for decision-making. The two items identif ied in the Terms of References (new significant issues and other issues) are the focus of this report. Bold faced statements are included to emphasize the main points of each section.
Topics
I believe that quantifying the rabbit problem as a pest needs to be addressed so that a clear statement of the goal of the introduction of the RCD virus can be specified. Additionally, a sound comprehensive cost/benefit analysis needs to be performed. There are various opinions of the extent of the rabbit problem in New Zealand. The undefined and non-quantified issues include:
* Are rabbits a pest everywhere they are found in New Zealand?;
* What degree are rabbits harmful to the environment?;
* What is the loss attributable solely from rabbit infestation?;
* What economic benefit can be attained from the rabbit?.
It seems that most of the reports and the public submission statements agree that there are benefits and damages from rabbits. The magnitude of these benefits and damages is not quantified. Furthermore, current control programs for the rabbit population are not well explored by the IIA Document in terms of the advantages and disadvantages and costs for each strategy. Opponents of the introduction of the RCD Virus do not agree with the conclusion that the current control methods are ineffective. The data from existing control programs are available and can be used to evaluate the effectiveness of the current control strategies and their impact on all of the issues that are influenced by the presence of the rabbit in the country. This would be a non-biased approach to answer questions related to the efficacy of the current strategies.
The IIA Document should include a section to evaluate control strategies that are currently not considered. A comprehensive evaluation of options for the control of rabbit populations is essential for a sound cost/benefit analysis. All the options of i mplementing the current control measures should be explored and evaluated. Considerations should be given to the option of the development of a fertility control strategy as an alternative method. The cost/benefit analysis produced by Brown Copeland and Co. (1996) should be evaluated and discussed.
RCV classification, history, and origins:
The IIA document has adequately addressed the RCV classification, history, and origins. As in any scientific review report, reviewers may have different opinions and interpretations of the presented data. The virus has been recently identified and the a vailability of literature on its classification is limited. Nevertheless, the effect and implication of the virus are well addressed. Some of the statements submitted by the public disagreed with the classification and the origin of the virus. The disagreement of the classification and origin of the virus, in my opinion, does not change the conclusion and has little impact on the decision making process for the introduction of the virus.
The epidemiology of the RCD has large areas of uncertainty. There are numerous questions that need to be answered. I feel that the answer to the following questions are essential before a sound scientific decision regarding the introduction of the virus can be made:
* 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 a rabbit population?
* What are the favorable environmental conditions for the spread of the disease in a rabbit population?
* What is the relationship between host susceptibility and dose of the virus?
* Is there an interaction between the exposure to this virus with other disease agents in the rabbit population or other animal populations?
* What are the limitations of the current diagnostic procedure for the disease in the rabbit population in terms of its sensitivity and specificity (i.e., misclassification)?
* What is the potential for the RCV to be a career for other viral agents?
* What is the persistent level of the RCV in the field and in which reservoir?
Due to the lack of field data and incomplete information about the disease many of these questions cannot be answered at this time. This level of uncertainty should be weighted in the decision making process. Research to answer these questions is recommended.
It is known that the introduction of any biocontrol agent is considered a risky issue. The public have the tendency to mistrust this method of control in contrast to conventional methods. The RCV is a relatively new virus and information about its nature is limited. Skepticism of the introduction of RCV is a valid stance for both scientific and public concerns. Exploring options for the control of the rabbit population that are better known than bio-control agents should be considered. The IIA document and its appendices included some of these options. Nevertheless, the document lacks a comprehensive evaluation of these options in an objective manner. I recognized that most of the quantitative information is missing, but a more objective approach util izing both risk assessment and cost/benefit methodology can be applied. There are several good examples for this type of evaluation particularly from the New Zealand animal health programs.
The IIA document and its appendices explored the literature for the host range of the RCV. Due to the fact that the virus is a relatively new entity, further emphasis is needed on the limitation of the current information. It is possible that this narrow host range be different in
the future with more available information. This point should be considered in the decision making process for the introduction of the RCV particularly for the long term effect.
To my knowledge there is no evidence that RCV infects humans. The public should be informed about the difference between infection and the presence of antibodies (i.e. serological response). There are several statements from the public submissions which implied that RCV has infected humans. Most of these statements are opinions of the individuals who submitted the statements. There is, however, a need to elaborate on the similarities and dissimilarities of the RCV and other Caliciviruses. Emphasis can be given to the heterogeneity of the Hepatitis E virus and RCV. The Kapikian et al. report (1996) is a good starting point for this elaboration.
My understanding is that the Australian scientists have conducted an epidemiological study to assess the impact of the virus on people working with or exposed to RCV. Findings from the Australian studies on humans should be evaluated in the consideration of releasing the virus in New Zealand.
Probability of RCV to mutate and consequences of mutation of RCV:
The extrapolation of the genetic analyses from SMSV to establish diversity of the Calicividae Family of viruses in nature and to assess the risk of "host switching" is speculative at this time. There is a need to discuss the risk of host switching and to determine the likelihood to have this scenario occur. As I emphasized in my original review, data are available
to evaluate this risk in terms of genetic heterogeneity of RCV to other Caliciviruses. The use of the Feline Calicivirus as an example for host switching could be addressed. The fact that FCV has been known for a long time and it has not shifted its host range or mutated should be discussed in more detail. The discussion about host switching of the RCV virus should include the fact that our knowledge of the number of strains sequenced is small and the history of the virus short. A conclusion from such a discussion would be limited.
The effect of introduction on New Zealand flora and fauna:
My familiarity with this topic is limited. The data and experience, however, of the introduction of myxomatosis in both Australia and UK should be considered as a model for the impact of the RCV introduction to New Zealand. I believe that the appendix submitted by Norbury on this topic was comprehensive except that the effect on livestock grazing was not mentioned.
As I stated in my original review of the IIA document, the method of releasing the virus is not clear. How the rabbits will be exposed to the virus in their natural settings was not described. I have requested information on this subject in my previous re view but I did not receive a response. The IIA document should specify the method of exposure, even though, the mode of transmission of the virus is unknown. Furthermore, the document should discuss the limitation of the method for releasing the virus in terms of its effectiveness with supported data and facts. Several scenarios may need to be presented. Additionally, the season for releasing the virus should be presented with supporting evidence for the selection of that particular season.
The monitoring program for the effect of the release is limited and is not described in detail. Due to uncertainty about the epidemiology of this disease, a comprehensive monitoring system should be considered. The monitoring program should be broad eno ugh to include all potential animal and plant species that could be affected by the introduction.
1. There are several issues that need to addressed and considered in thedecision making process for the introduction of the RCV. Although some of these issues have already been addressed in the original IIA document, no solution with a quantitative level of certainty were given to support a decision for the introduction of the virus. The IIA document and its appendices extensively covered most of the issues surrounding the introduction of the RCV but due to limitations in the available information about this virus and the disease, this coverage was not sufficient for a scientific decision to support or reject the application of the introduction of the virus. Specifically, the following issues require further expansion:
* A clear statement about the short and long term goals of the introduction of the virus. The applicant group may consider answering the following questions:
* What are the short term goals to be achieved by the introduction of the virus?
* What are the long term goals?
* What region(s) of the country are targeted for these goals?
* What length of time will take to achieve the goals?
* How long will they be effective?
* What are the potential effect if there is a failure to either achieve or confine the introduction of the virus?
All of these answers to these questions should be supported with facts.
* The issue of the viral mutation and host switching would require more explanation with emphasis on scientific facts and scenarios. Due to the limited scientific literature on this subject, comparison with other similar viruses may be used to address this issue.
* Non-conventional rabbit control strategies should be explored even if these strategies are not currently available or applicable. Benefits and damages from these strategies would assist in the decision making process.
2. A clear objective of the release strategy and a comprehensive cost/benefit analysis are needed before a sound decision can be made. The comments from the Ministry of the Environment (ref. 0 3-1-7 of July 17, 1996) contain a good outline for a sound cost/benefit analysis for this purpose. The presented cost/benefit analysis is not comprehensive in the alternative options or in its broad benefits/damages. A team of experts from the various involved disciplines is required for this task.
3. The epidemiology of the disease is limited particularly in the available information about the natural setting of the disease. Answers to the questions listed in the above Epidemiology Section would be required to perform sound cost/benefit and risk as sessment analyses. I believe that a scientifically based decision on the introduction of the virus would require both of these analyses.
4. The method of releasing the virus to the rabbit population needs to be described and supported by scientific facts. Monitoring of the release and its impact (both short and long term) should be detailed. I believe that there is a need to create a tea m of experts to develop a monitoring system that is broad enough to assess the impact of the RCD and provide plans to intercede if potential damages arise.
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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