6 THE VIRUS AND ITS EPIDEMIOLOGY

6.1 INTRODUCTION

This section summarises the issues raised by submitters regarding the rabbit calicivirus (6.2) and its epidemiology (6.3).

The discussion of the virus itself is organised into five main topics: the effectiveness and suitability of the RCD virus as a biocontrol agent in New Zealand, its propensity for mutation and changes in host range, its host range, its survivability, and matters concerning its classification, history, and origins. At the end of each of these five subsections any deficiencies perceived in the Application are categorised as matters to be addressed or requiring further information.

6.2.1 RCD AS A BIOCONTROL AGENT

A large number of submissions discussed the effectiveness and suitability of the rabbit calicivirus as a biocontrol agent in New Zealand. Both advocates and opponents of the introduction of the virus contributed significantly to the debate.

Issues

The main areas of concern were:

  • the safety or otherwise of the virus;
  • assessments of its effectiveness and suitability as a biocontrol agent;
  • its ability to maintain stated pastoral and environmental goals over time;
  • its use with other methods of rabbit control;
  • the history of importing other organisms into New Zealand; and
  • the irreversible nature of the virus's release in this country.

Safety

Discussion about the issue of safety was very polarised. Several submissions in support of the introduction of RCD emphasised various aspects of its safety. One supporter (359) pointed out that the Application had brought together significant research on the virus which proved it safe in Asia and Europe, while another (498) suggested that the biological control of pests is essential to maintain a safe and clean environment. A third supporter (194) maintained that the only real risk is non-introduction and that all other risks are only "emotive theories" which have not occurred in any other countries. By contrast several opponents of the virus's introduction questioned whether it was a safe proposition. Their comments ranged from noting that RCD was beyond the control of existing vaccines to claims that its proposed release was "dangerous" (376) and "germ warfare" (423).

Effectiveness and suitability as a biocontrol agent

Comments regarding the effectiveness and suitability of RCD as a biocontrol agent were also very polarised. Most discussion on this particular issue come from the supporters of introduction, although opponents also made a significant contribution to the debate. Generally, supporters clearly argued their case for introduction by citing the advantages and benefits of RCD as a biocontrol agent, whereas submitters holding the opposing view were more likely to substantiate their case by referring to its disadvantages and costs.

Submitters referred to a wide range of economic and environmental advantages or benefits that they believe will reaped by the nation should RCD be introduced. These benefits are listed below:

ECONOMIC: A cost-effective method of rabbit control; savings in rabbit control costs; eductions in lost revenue from competition for grazing; smoother income and expenditure patterns between years; increased farm production, more expenditure on items such as fertiliser, seeds, amenity planting, fencing, upgrading equipment, weed and possum control; debt reduction; improvements in the economic viability of farming properties; and the improved vitality of rural communities and downstream industries.

ENVIRONMENTAL: Maintain rabbit populations at a sustainable level; an effective means of control across property boundaries; long term improvements in land conditions and grazing; better herbage thereby improving water retention and soil fertility; the stabilisation of erosion-prone country; rare and endangered species would be conserved in arid regions; reduced use of other tools such as 1080 poison and pindone; less risk of TB due to a decline in the mustelid population; and reduced numbers of predators.

Comments from some supporters of the introduction of RCD indicate that they believe its environmental benefits could be very significant. One of them (348), for example, compared rabbits to vermin like mice and rats. Another (444) asks "What is more abusive - 1 million tonnes of 1080 poison or a selectively naturally occurring rabbit disease?". While a third submitter (555) states that RCD is "a very efficient, humane and environmentally friendly method of rabbit control".

By contrast opponents almost entirely focussed their comments on the possible disadvantages of the introduction of the virus. Some opponents disputed the effectiveness of the virus by noting that it would only achieve a partial-knockdown of rabbit populations or that its effectiveness would be confined to certain parts of the country. Other submitters felt it would be uncontrollable or unpredictable. One submission (682) which did not clearly indicate its stance on the Application commented that:

"RCD may cause worse damage to irreplaceable components of our native biodiversity than rabbits ever did. Farmers do need a solution to their rabbit problem but the benefits of RCD over conventional methods of control are not high enough to justify the significant environmental risks."

An opponent (493) expressed similar sentiments by describing RCD as "totally unsuitable" as a biocontrol agent because of its uncertain effectiveness and ecological effects, and the major risks it poses for farm animals, wildlife and humans. Others, who considered RCD unsuitable, maintained that there is no cure from infection by the virus nor is there any vaccine available.

Ability to maintain stated goals over time

Assessments of the success of the RCD virus in maintaining stated pastoral and environmental goals over time were almost entirely made by opponents of its introduction. One supporter (367) did acknowledge that eradication of rabbits would not be possible with RCD, and another (399) admitted it would not solve the problem. Some opponents, however, majored on its temporary nature; describing it as a short-term solution, or a short-term fix, with short-term gains that were not worth the potential risks. Another submitter (460) was concerned that it would merely defer the problem of land management. Furthermore, many opponents, and a submitter whose stance on introduction was unclear (398), 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."

Some opponents were concerned that oscillating rabbit populations would disrupt predator control of rabbits, while another (606) regards the cyclical nature of the virus as a problem for other species because "alternate prey species, such as invertebrates, would be subject to increased predation with every swing or cycle". A particularly graphic scenario of the possible consequences of failing to eliminate the entire rabbit population was presented by one submitter (500) who predicted that the present means of control will not exist when rabbit numbers rebound: the hunters will have found other activities, 1080 poison will no longer be manufactured, and the predators will have switched to other species or died. "In short the rabbit problem will be worse than ever." (500).

Use with other methods of rabbit control

A number of submissions, representing the whole range of positions with respect to the introduction of RCD, recognised that biocontrol was not the complete solution to the rabbit problem and advocated its use with other methods of rabbit control. Most advocates of this integrated approach, however, were supporters of its use as a biocontrol agent. 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."

Another submitter (108), who indicated qualified support for the use of RCD, commented that it would only have short-term effects on keeping numbers under control if it was not backed up with a sexually transmitted disease that would affect the rabbit's reproductive capability. Two submitters, whose stance regarding introduction was unclear, also addressed the need for integrated control. One (398) contended that other control methods must be positively enforced in conjunction with RCD, while the other submitter (478) questioned the assumption on p.59 of the Application that the release of RCD would result in high initial knockdowns and continued control when used with other control methods. Few opponents discussed this matter of integrated control, although two of them suggested that if RCD is introduced it should be combined with land management. After observing that rabbits appear to have thrived in "relatively degraded environments", one of these submitters (697) proposes that a planned introduction of the virus be part of a wide range of "measures to rehabilitate the arid areas" including retiring land from farming, revegetation efforts, and the exploration of alternative land uses.

History of importing other organisms into New Zealand

Some submissions referred to the history of importing other organisms into New Zealand when discussing the suitability of RCD as a biocontrol method. Almost all of these comments came from individuals and organisations opposed to the virus's introduction. Phrases such as "a past history of disasters" (548), "disastrous history" (455), "previous disastrous record" (207) "disastrous introductions" (685) and "unfortunate introductions" (511) portrayed a long negative experience with various types of introduced species in New Zealand. This negative experience was then used to emphasise the dangers of introducing another new organism, i.e. RCD, to the ecosystem. One submission (282), for instance, noted the ongoing detrimental effects of introductions such as wasps, gorse, possums and herbicides on the environment and warned that New Zealand cannot afford to take any more chances with nature. An opponent of introduction (500) maintained that "With the benefit of hindsight I doubt whether anyone would want to introduce weasels and stoats to control rabbits", while another (685) took the view that the country should not import any more "immigrant killers".

Irreversible release

The irreversible nature of the virus's release in this country was noted by a few submitters (mainly opponents). They pointed out that once RCD was released into NZ's environment the decision could not be reversed, neither could the virus be withdrawn if it proved to be unsatisfactory as it would be impossible to eradicate. Other submitters sought some assurance from the Applicants that RCD could be eradicated if it became necessary. An opponent (554) wondered if the country was going to replace one mistake (the rabbit) with another (RCD), as a virus can neither be traced nor controlled, and may become a permanent feature of the environment.

Matters which submitters suggest should be addressed or require further information:

Require research to make useful predictions about the outcomes of a release of RCD in New Zealand (e.g. 477).

The long-term marketability of our export produce must be considered (e.g. 266).

Insufficient information about adverse impacts and strategies for dealing with them (e.g. 513).

Insufficient attention given to the adverse effects on native invertebrates (e.g. 606).

Virus-resistant rabbits will emerge eventually and the rabbit problem will reach plague proportions again in the future. How will rabbits be controlled then? (e.g. 641).

The IIA does not address land management as part of an integrated pest management strategy (e.g. 460).

A gap in knowledge of the cost-effectiveness of RCD in controlling rabbits in the short or long term (e.g. 478).

6.2.2 PROPENSITY FOR MUTATION

A large number of submissions commented on the propensity for mutation and changes in host range of the Rabbit Calicivirus. The majority of these comments came from individuals and organisations opposed to the introduction of the virus.

Issues

The main areas of concern were:

  • the propensity for mutation;
  • changes in host range;
  • the damaging effects of mutation and host switching; and
  • the adequacy or inadequacy of scientific knowledge about the propensity of RCD to mutate and change hosts.

Propensity for mutation

Views regarding the propensity of RCD to mutate were widely divergent. The supporters of the virus's introduction only made a minor contribution to this debate. Some made remarks which indicated that they regarded the risk of mutation as unlikely, negligible, or not a realistic possibility. Other supporters maintained that there was no evidence of the virus mutating and affecting humans. Submitters who qualified their support for the introduction of RCD, however, had reservations about its propensity to mutate. They had concerns about the unknown nature of virological mutation, its potential to cause a sublethal/latent infection and that it might have damaging effects on the environment.

The other submitters, whose stance was either unclear, or who had some degree of opposition to the importation of the virus, assumed that it was likely to mutate. One submitter (478), belonging to the former group, took the view that the heading "risk of mutation within rabbit calicivirus"on p.141 of the IIA was misleading given that it is natural for viruses to mutate, and claimed that the consequences of mutation should be considered a risk instead. Another (429) added a different perspective to the debate by suggesting that both viruses and rabbits are capable of "genetic mutation and great diversity".

While many opponents briefly noted the concerns they felt about the virus's potential to mutate, others provided some evidence to substantiate their case. One group of submissions pointed out that viruses are known to mutate and some cited AIDs and mad cow's disease as examples of how viruses can mutate and infect humans. Others refer to recent experiences with RCD in China and Europe . One submitter (213), for instance, reports that in 1984 the calicivirus changed in China and started killing rabbits and asks "Why did this occur and what is stopping it from mutating into a more virulent form that could affect other species or even humans?" Another (469) notes that since 1994 RCD has evolved into several identifiable strains with significant differences in RNA nucleotide sequences in Europe.

A few submitters entered into complex technical discussions about viruses. For example, one opponent (362) claims that, as an RNA virus, RCD is more prone to mutation and recombination than DNA, and that RNA viruses have shorter generation times and their polymerases are more error prone. Whereas another opponent (493) refers to the evolvability threat of the RNA virus as an area of dispute and contends that it is untrue to portray the genetic variability of calicivirus as being the same as other viruses (as in s6.10.9 p.144 of IIA).

Changes in host range

Most submissions focussing on the issues of mutation and host range tended to discuss them together. Thus opinions regarding changes in the host range of RCD, like those expressed about the propensity of the virus to mutate, were deeply polarised between supporters and opponents of introduction. And again the comments from opponents were much greater in volume than those of supporters.

The debate followed a similar pattern as outlined with regard to the issue of mutation. Supporters generally dismissed or minimised the risk of RCD crossing or jumping species. They used phrases such as "host specific" (196), or "species specific" (555), to describe the virus, while one of them described talk of cross infections as "scare tactics" (228). Another supporter (309) endorsed the statement in s6.10.7 of the IIA that the risks of changes in the host range is very low and commented that:

"Neither the natural spread of RCD in Europe and Asia nor the use of live feline calicivirus vaccines have been shown to be a risk to other species. Therefore, a ban on the importation of RCD into New Zealand cannot be justified."

A submitter (76) who gave more qualified support to the virus's introduction was more circumspect, however, and suggested that there is a need to investigate further the potential for RCD to affect other species.

There were also comments from submitters whose stance with regard to introduction was unclear. Two of them made significant observations about changes in the host range. The first (478) concurs with the Application that such changes are extremely rare, and notes that there is only one documented case which is now under debate. While the second submitter (796) expresses concern that the chance of RCD switching hosts has not been stated as a probability in the Application.

Opponents, following the approach they adopted regarding mutation, tended to emphasise the possible risks of RCD switching or jumping species. For example:

"There is no guarantee that the virus will not mutate and attack some other host than rabbits." (719)

"... the possibility of them [the virus] mutating and jumping species is very frightening." (29)

"... nothing is yet known about the potential of the virus to cross species after long-term host-viral co-evolution in the field". (479)

Damaging effects of mutation

There was a great deal of concern about the risk of the virus infecting indigenous or native species and humans. In one submitter's (137) view, however, a rabbit-borne virus was more likely to pass directly to other mammals than to infect birds, reptiles or invertebrates in general. A few submitters noted that four out of the five known groups of caliciviruses jump species and suggested that similar behaviour could be expected from RCD. Others cited the possible origins of RCD in the European Brown Hare Syndrome and the development of antibodies in a Mexican laboratory worker as indicators of the virus's ability to change hosts.

A few submitters also commented on the damaging effects that mutation and host switching by the virus might have on the environment. Some of them expressed concerns about livestock becoming infected and endangering New Zealand's meat exports. Others considered that RCD may kill family pets or cause skin problems or other disorders in humans.

Adequacy of scientific knowledge

Another matter that generated some interest among submitters was the question of whether the scientific knowledge with respect to the propensity of RCD to mutate and change hosts was adequate or not. Again the majority of comment on this issue came from the opponents of introduction. Not surprisingly the supporters, who specifically mentioned the scientific evidence cited in the Application, accepted its adequacy. Opponents, by contrast, were reluctant to accept that this was the case. One of them (129) considered that the arguments cautioning against the risk of a mutating virus are as plausible as those claiming it is safe and the qualifications of those making the various claims were equal. Another opponent (201), after noting the differing views among the scientific community, wanted to know who the public should believe. A third (585) pointed out that nobody seems to know where the virus originated, either biologically or geographically, and that absence of evidence regarding host switching is not necessarily evidence of the absence of this phenomenon. Other opponents mentioned the short history of the virus; with one of them (493) describing the time lapse between discovery of RCD and the categoric statement in the IIA that it would not jump species as "very minimal". Furthermore, one submitter (552) believes that scientists in New Zealand have shown an inability to cope with the dimensions of "time" and the "environment", and cites the debate over 2-4-5T and other agricultural chemicals as an example of how the advice of scientists has delayed bans on these substances for years. The submitter attributes these delays to science in New Zealand having had a narrow focus because of undue influence from agricultural lobby groups.

Matters which submitters suggest should be addressed or require further information:

The rate at which the rabbit calicivirus is changing in laboratory and field conditions (e.g. 768).

The probability/risk of mutation (e.g. 400, 652).

The existence (or otherwise) of any reported cases of major mutations in viruses leading to sudden major host changes allowing a virus to suddenly infect a species previously shown to be unresponsive to the virus (e.g. 736).

The identification of other mutations that can originate from RCD (e.g. 784).

The capacity (or otherwise) of the virus to switch species (e.g. 334, 707), and the safety of the virus in this respect must be made certain and publicly announced (e.g. 707).

The chance of the RCD virus switching or extending its host range is not expressed as a probability (e.g. 796).

The research is inconclusive with regard to host species switching and genetic mutation (e.g. 612).

Interspecies investigations should include movements of the San Miguel-Vesicular Exanthema Caliciviruses, the feline Calicivirus, the Hepatitis E Caliciviruses of humans and the Nowalk-like group of human Caliciviruses (e.g. 236).

The possibility and consequences of antigenic drift, attenuation of RCD, changes of virulence and frequency of mutation (e.g. 478).

RCD's known existence as a pathogen is very brief (e.g. 651).

More knowledge is required of RCD (e.g. 418).

More research on what happens when the food source of the rabbit calicivirus is exhausted (e.g. 10).

Views of virologists such as Dr Alvin Smith need to be taken into account (e.g. 796).

6.2.3 HOST RANGE

A large number of submissions discussed the host range of the Rabbit Calicivirus and the laboratory studies of that range. Most of these comments came from organisations and individuals who were opposed to the introduction of the virus.

Issues

The main areas of concern were:

  • the host range;
  • the laboratory studies of the host range;
  • the merits of field studies of the host range compared with laboratory studies; and
  • the validity of conclusions regarding the host range which were derived from a review of the scientific literature;

Host range

Much of the discussion in the submissions about the host range of RCD also expressed concern about the risk of the virus jumping or switching species (see section 6.1.2). One submitter (673) suggested that there were three practical questions that needed to be answered:

"1) Has RCD ever infected any other species other than the European rabbit? 2) Is it now infecting any other species? 3) Could it be expected to infect any other species?" (673)

Comments by supporters of the virus's introduction ranged from apprehension about the safety of other species to assurances that the virus is host specific. One supporter (413) remarked that international research indicates only one host and that "there has not been any definitive evidence presented yet to show that the virus can replicate in other host species".

Yet the comments on this issue by submitters, whose stance was unclear, and those who were opposed to the importation of the virus, reveal a very different view of the scientific evidence. Statements maintaining that further evidence was required or that the claims for host specificity were supported by insufficient data or poorly founded indicate a high level of dissatisfaction with the scientific data that was presented in the IIA. One opponent (362), moreover, challenges the statement on p.114 of the IIA that "There are no reports of RCD outbreaks in other Leporiade species or related members...." by referring to documented accounts of hares being infected with RCD as early as 1986 in China and Italy. Some submitters also contest the claim that the virus is host specific. For instance, one (391) notes that it would have been impossible for rabbits to convey RCD from China to Spain in four years and concludes that some other host must be responsible. Furthermore, another submitter (448) reports that pigs contracted Swine Vesicular disease when they were fed with infected seal tissue, and asks what will happen when infected rabbit meat is fed to other species.

Laboratory studies of host range

The laboratory studies of the host range conducted in Australia attracted a lot of criticism from submitters whose stance on introduction was unclear and opponents. Few supporters, on the other hand, made comments about these studies. They usually referred to the tests to emphasise their view that there is a minimal risk of other species becoming infected by the virus. Nonetheless, one supporter (309) did suggest that the tests on other species be expanded to sample hares, species known to feed on carrion, and representative animals in South Australia that have been exposed to flies contaminated by RCD.

Criticism from opponents, and those submitters whose position was uncertain, fell into three main categories: comments which were briefly dismissive of the laboratory studies, more focussed criticism, and rigorous critiques. The first category described the tests on bats and kiwis with phrases and words such as "a methodological disaster" (308 quoting Dr Neil Cherry), "flawed" (278, 549, 727), "inconclusive" (246, 591) and "ridiculous" (545). More specific concerns expressed by the second category included the small size of the sample of kiwis and bats which were tested, the small doses of the virus which were injected into the kiwis and bats, and the need to test a wider range of native fauna.

A considerable amount of time and energy was expended by the authors of several submissions which rigorously critiqued the laboratory studies of kiwis, bats, and other animals in Australia. Much of their criticism is very technical. What follows is a summary of their major concerns.

Criticisms made by several overseas scientists about the specific tests performed by CSIRO and MAF in Australia were summarised by one of the submissions (673). It listed these criticisms as 1) the 30% cut off point used to detect antibodies was considerably higher than normally used overseas; 2) when detecting the presence of infection in blood and tissue samples some test species should have been necroprised earlier than 14 days; 3) high levels of antibodies may be detected in the blood for a long time after infection and thus their antibody levels would have increased accordingly; and 4) with a 0-3% negative cut-off point mice, chickens, red foxes, brown falcons, seagulls, and kiwis registered above 3% and yet it was stated that no virus infection occurred (673). (It should be noted that the numerical values in the above paragraph are taken directly from the submission.)

A submitter (1000), who also opposes the introduction of the virus, expands on these criticisms of the analytic tests by maintaining that there is no evidence that "the AAHL conclusively ruled out involved involvement of parvovirus, nor any other virus through any of their analyses or assays". The submitter then adds that the "incorrect assumption that the Rabbit Calicivirus is the sole and confirmed infective agent leads to false negative results in the Australian and New Zealand non-target species and could well be a problem in other studies" (1000). After examining the autopsy results on the bats and the kiwis, this submitter, found that most of the results described for the kiwis were consistent with infection by RCD.

Another submitter (478) observes that an inability to culture rabbit calicivirus in cells (of other species) cannot be taken as evidence of the restricted host range of the virus as the rabbit calicivirus has not yet been cultured in rabbit cells, but is well known to infect rabbits. Referring to the IIA, this submitter (478) notes that the discussions "of the ability to grow viruses in tissue culture and host specificity is somewhat confusing" and of "a relationship between the host range of viruses is somewhat speculative". An opponent (362) disputes the interpretations placed on the scientific tests conducted in the Australian testing programme that concluded that certain pathological changes were not due to RCD as the affected organs did not contain the virus. This submitter also questions the approach of looking for the same clinical signs in the tests by claiming that RCD may not necessarily cause the same signs of clinical disease in other species, and notes that the inoculation procedures for the tests on kiwis and bats did not follow the standard practice of administering by more than one route.

Claiming that all the negative results of tests on non-rabbit species are without merit because of the flawed experimental design, another opponent (376) of introduction of the virus concludes "that there was compelling evidence that RHD [RCD] established infection in a number of test species and that RHD is not host specific".

Finally, a submitter (695), who describes the research results in the IIA as "unacceptable", proposes that further investigations need to include a wide range of dosage levels, transmission routes, animal species, and health status of the animals and birds. Furthermore, this submitter maintains that the results must be measured over a wider time frame, better controls must be established, and other methods of research must be employed to verify the results of the ELISA testing.

The merits of field studies

A few submissions addressed the merits of field studies of the host range by comparing them with the laboratory studies. They either emphasised that field evidence was more valid than that provided by laboratory studies, or considered that it provided a different perspective on the use of RCD as a biological control. One of the submitters (477) belonging to the former category, for example, expressed the view that "field evidence tends to provide more valid reassurance, that this agent is less likely to produce infection in other species, to the extent that predictions can be made".

Conclusions from the scientific literature

The validity of conclusions in the IIA regarding the host range, which were derived from a review of the scientific literature, was challenged by two submissions. One submitter (393) disputes the conclusion that the agent of RHDV is restricted to European rabbits and, after referring to p.152 of the IIA and the scientific research documented on pp.22-30 of the Bureau of Resource Sciences of Australia (August 1996) report, concludes that "it is wrong to describe these studies as 'in no case was evidence found'...". Another submitter (1000) also notes that the international literature was reviewed in the Bureau of Resource Sciences (1996) report, and states that this literature identified antibody positive reactions in several species of animals and birds. This submitter (1000) comments that these results were dismissed by the Bureau of Resource Sciences as being due to Rabbit Calicivirus because calicivirus was not found in the infected organs, and suggests that the infective agent may be parvovirus which would not be identified if the tests were only looking for calicivirus.

Matters which submitters suggest should be addressed or require further information:

An independent panel of scientists is required to review the scientific validity of the experiments and the results obtained (e.g. 176).

The report of the Australian tests for RCD in human sera has not been reviewed by experts (e.g. 755).

There is no discussion in the Application of whether the 'transmission medium' was infected (e.g. 391).

A lack of information about the antigen sources and the method of determining the cut-off criteria used in the ELISA tests (e.g. 391).

The laboratory testing of the host range omits an historical perspective of the rabbit calicivirus and other similar viruses (e.g. 137).

The Application is based on full test results for only two NZ native species (e.g. 755).

A more thorough investigation of the effects of RCD on kiwis is required. (40).

A test of European bats is required (e.g. 137).

The data is inadequate to provide evidence that the virus does not infect other species (e.g. 176, 601).

Further study is required as many species are susceptible to increases in antibodies (e.g. 648, 755, 768).

A guarantee that the disease will not spread to other species (e.g. 458).

Further clinical studies on the possible impact of RCD on humans (e.g. 609).

6.2.4 THE VIRUS’ ABILITY TO SURVIVE

Very few submissions commented on the survivability of the virus. Nearly all of these submissions were from the opponents of importation.

Issues

The main areas of concern were:

  • the tolerance of the virus to heat, cold and desiccation; and
  • the survival of RCD in the faeces of grazing and scavenging animals, and dogs.

Tolerance

One submitter (478) points out that the IIA, on pp.121-122, notes that no standard thermal degradation studies of RCD currently being released in Australia have been conducted , and states that viruses are considered more stable at cold temperatures between -5 and -70 degrees centigrade. Furthermore, this submitter notes that no formal studies of the effects of desiccation on rabbit calicivirus are reported in the IIA. Another submitter (101) adds that New Zealand's climate is cooler and damper than Australia.

Survival

Two submissions expressed concerns about the survival of RCD in the faeces of grazing and scavenging animals, and dogs, and that these faeces could be a source of infective RCD for other species.

Matters which submitters suggest should be addressed or require further information:

The survival of RCD in the faeces of dogs, and grazing and scavenging animals (e.g. 459).

6.2.5 THE VIRUS - CLASSIFICATION, HISTORY, ORIGINS

A large number of submissions discussed the description and classification, strains, origins and history of the Rabbit Calicivirus and made comparisons with other viruses of the same family. The majority of these submissions came from individuals and organisations opposed to the importation of the virus.

Issues

The main areas of concern were:

  • the description and classification of the rabbit calicivirus;
  • the strains of the rabbit calicivirus;
  • the origins and history of the virus;
  • comparisons with other viruses of the same family; and
  • the adequacy or inadequacy of scientific knowledge about the rabbit calicivirus.

Description and classification

Some submissions dispute the description and classification of the rabbit calicivirus as presented in the IIA. One of them (673) points out that a number of strong differences of opinion have emerged about the nature of RCD: i.e. is it a calicivirus, or a calicivirus and a parvovirus, or just a parvovirus? If it is a calicivirus is RHD/RHDV the same as RCD? Do the Australians have the same virus as the Italians, the English, the Americans, or the Chinese? A second submission (601) comments that there seems to be scientific agreement on the type of the virus which causes the haemorrhagic disease - calicivirus, parvovirus, retrovirus, prion disease etc. Moreover, a third (362) notes that scientists in the United States and China believe a parvovirus is involved as an infective agent, while those in Europe, Australia, and New Zealand believe the rabbit calicivirus acts alone. Other submissions also raise the possibility that a parvovirus may be involved as the infective agent. Referring to the source strain CAPM V-351, which was imported to Australia from Czechoslovakia, one of the submitters (1000) claims that the biological agent is not pure rabbit calicivirus because two infective agents are identified and described: rabbit calicivirus and a parvovirus.

Not only is there uncertainty about the exact nature of RCD and its infective agent, but there is also considerable disagreement about the classification and nomenclature of the virus. While some submitters (236, 361) maintain that the correct label for RCD is "Rabbit Viral Haemorrhagic Disease" [RVHD], others (391, 648, 1000) consider that "Rabbit Haemorrhagic Disease" [RHD or RHDV] best fits the description of the syndrome. One of the latter group (391) believes that the term 'rabbit calicivirus' is "an ambiguous neologism" because it presumes the virus itself is the agent. Another member of the same group (648), moreover, reports that RHD is the term which is used almost universally overseas, but RCD is used in Australia and New Zealand.

One of the submissions (361), which suggests RVHD is the correct term, maintains that RCD is "a sanitised name" for "a blood-haemorrhage and clotting type of hepatitis" that has "bubonic plague potential". Others report that the USA classifies all caliciviruses, except feline, as Foreign Animal Disease agents, and that RCD is a notifiable disease in France and the United Kingdom.

Strains of the rabbit calicivirus

A few submitters, representing the entire range of views with regard to the virus's introduction, discussed the strains of the rabbit calicivirus. There is little information in the IIA about the relationships between the various strains of the virus according to a submitter (478). And, while one supporter (379) maintains that the proposed source of the virus is a pure strain with no risk of contamination, other supporters suggest that there are some uncertainties that need to be considered:

"There is a risk of importing an impure inoculation, bringing unwanted animal disease with it such as myxomatosis and foot and mouth disease. There must always be a check to ensure only pure strains are imported." (619) and

"...the history of highly virulent viruses is that sooner or late mild variants appear which can exist in a more stable equilibrium with the host population." (477)

On this subject of new strains, an opponent of introduction (362) reports that Italian scientists have discovered a non-pathogenic version of RCD which does not produce any clinical signs of the disease. While another opponent (768) claims that European researchers have identified sufficient changes in rabbit calicivirus to classify them as new strains, thus demonstrating that they may change over relatively short periods and possibly affect their infectivity and replication rates.

Origins and history

The origins and history of RCD generated a lot of discussion by opponents of its importation. Many of them consider its uncertain origins and evolution, and the brief period since it has been identified, as reasons for a cautious approach to its release.

"Where it came from and how it developed is not known, neither has its potential to kill other than rabbits been explored." (316)

Other submitters directly contested the claims in the IIA about the origins of the virus. One (391), whose stance is unclear, criticises the use of "questionable antibody results to suggest that a 'non-virulent form' of RHDV existed in Europe prior to the recognition of the disease in 1984", and concludes that there is no likelihood of it being an endemic disease of rabbits prior to that date. Another submitter (478) with an unclear stance, however, takes a different view by noting that the debate over the history and possible origins of the virus is still continuing; with the options being a non-pathogenic rabbit virus or a virus which switched hosts from another species.

A few submitters confront the issue of the virus's origins and history by proposing their own theories. While acknowledging that the origins of RCD are unclear (pp.107-108 of the IIA), one of these submitters (695) suggests it may have developed from a benign form or through infection from European Brown Hare Syndrome in hares. Another submitter (1000) proposes this hypothesis regarding its origins:

"European strains of RHDV were originally calicivirus rich and the Chinese rabbits hosted a virus which was parvovirus rich. When European rabbits were introduced to China the calicivirus and the parvovirus mixed to form an infective strain of RHDV. After the outbreak in China the parvo-enriched strain was carried back to Europe." (1000)

A third submitter (361) maintains that RCD behaved like a mutant plague in China in 1984, and then in Europe, wiping out the rabbit farming industry. This submitter then observes that:

"It is not unlikely that the virus was of human hepatitis E residence before adopting the Chinese rabbit as host. The infective virus has not been identified and could be one of several strains." (361)

Comparisons with other viruses

Closely associated with the issue of RCD's origins are comparisons with other viruses of the same family. Only a few submissions commented on this matter however. One submission (554) notes that caliciviruses are an evolving area of research. Then adds that the wide number of species cited (p.127 of the IIA) indicate that this is a foundation disease, a pool from which a number of types has been derived, and suggesting the likelihood of changes and crossovers within the separate types. Some submissions express concerns about the interspecies transmission that has occurred in other caliciviruses; with one of them (177) reporting that calicivariade have been known to cause human diseases such as hepatitis E, diarrhoea, pneumonia, encephalitis, myocarditis and abortion. Others state that RCD is an RNA virus, and comment that RNA viruses are unstable. One of these submitters (478) points out that "The biological consequences of possible changes in viral RNA are antigenic change, host cell specification changes; and changes in disease patterns and virulence". The outcomes of these changes in viral RNA, according to this submitter, are unpredictable.

Adequacy of scientific knowledge

A number of submissions discussed the adequacy or inadequacy of scientific knowledge about the rabbit calicivirus. Although the majority of these comments were expressed by opponents, the supporters of introduction did express some opinion on the matter. Although most supporters appeared content with the adequacy of the scientific knowledge about the virus, at least one supporter (285) noted there were gaps in the information and suggested that more research is required. Opponents, on the other hand, expressed their view of the current state of scientific knowledge on this subject by making remarks such as "inadequate information" (487), "little known" (776), "little understanding" (291), "not enough known" (458) and "limited knowledge" (380). Some opponents, moreover, were more explicit in their comments and either identified specific deficiencies in the current state of knowledge or suggested what additional studies need to be undertaken (see also the "Matters to be addressed/ or requiring further information" section below). Those in the former category stated that there were no long-term studies of the virus conducted in Europe or Asia, the assessment of the characteristics and effectiveness of the virus was inadequate, and note a general lack of information about the virus's origins, mechanisms of spread, and sources of infection. While a submitter (339) in the latter category called for a comparative study of the MCF and RCD viruses.

Matters which submitters suggest should be addressed or require further information:

More research on RCD is required (e.g. 285, 487).

A long-term study of RCD to evaluate the potential risks (e.g. 45).

More information about the origins of RCD (e.g. 591, 648).

Test North American lagomorphs for EBHS to trace the origin of the virus (e.g. 648).

The latency and the reactivation of the rabbit calicivirus, its association with specific aspects of cell function, its combination with other viruses in the same group, and the viral proteins associated with infectivity need to be investigated (e.g. 768).

The IIA does not discuss what causes acute liver necrosis and catastrophic disseminated intravascular blood clotting (e.g. 493).

More information about non-virulent forms of RCD is required (e.g. 258).

Insufficient information exists to enable the level of the variation in the virus to be adequately assessed (e.g. 176).

The IIA omits the information that the officially recognised name of RCD is viral haemorrhagic disease (VHD); a virus which is on List B of the International Animal Health Code (e.g. 478).

The effects of RCD on animals eating rabbits infected by the virus (e.g. 334).

More understanding of caliciviruses, their method of transmission, their potential for host switching and the preparation of vaccines is required (e.g. 294).

The points raised by Dr Alvin Smith about the calicivirus have not been adequately negated, and the issues about the calicivirus phylogeny and whether the calicivirus is a parvovirus need to be resolved (e.g. 400).

A thorough review of the international review of the scientific literature on virus behaviour (e.g. 460).

MAF needs to provide more information to the public about the virus and its effects (e.g. 641).

6.3 THE EPIDEMIOLOGY OF RCD

The discussion of virus epidemiology is organised into four main topics: the virus effects on the host, immunogencity, the spread of the disease and the method of transmission. At the conclusion of each of these four subsections any deficiencies perceived in the Application are categorised as matters that need to be addressed or requiring further information.

6.3.1 VIRUS EFFECTS ON THE HOST

Only a small number of submissions commented about the effects of the RCD virus on the target species and the effects in Host Species. Most of these submissions were from organisations and individuals who were opposed to its importation into New Zealand.

Issues

The main areas of concern were:

  • the effects on target species;
  • the effects in host species; and
  • the inadequacy of the information on epidemiology.

Effects on target species

Some opponents of importation noted that the effects of RCD in killing-off rabbits were limited. In dry parts of Australia and the island of Madeira, for instance, they report that only a proportion of the rabbit population succumbed to RCD. Thus, without other forms of control, a remnant of the rabbit population with immunity to the virus may flourish and restore the population to previous levels.

Effects on host species

Other submissions discussed the effects in host species. Whereas opponents generally had concerns about the possibility of RCD switching to another host species from the European rabbit, one advocate (367) of importation was satisfied that the virus is highly host specific. Another submitter (383) pointed out that an age cohort of rabbits (3-10 weeks) is not susceptible to the disease and becomes resistant. One submission (478) examined the clinical signs, pathogenesis, morbidity, mortality, virulence, variations in susceptibility and time to death of the wild rabbit when infected with RCD, and identified some omissions and further matters to be addressed in the Application (see below).

Adequacy of information on epidemiology

A submitter (477), who expressed qualified support for importation, had some reservations about the adequacy of information on epidemiology contained in the Application. In particular this submitter observes that the chapter on epidemiology in the Application "demonstrates very clearly how seriously inadequate information on the epidemiology is", notes that the AAHL in Australia had no trained epidemiologist on its staff and that the

release of RCD to Wardang Island occurred with a number of key epidemiological questions remaining unanswered.

Matters which submitters suggest should be addressed or require further information:

Investigations relating to intermediate hosts (e.g. mice, rats & insects) (e.g. 768).

No mention that rabbits dying of RCD seem to have good body condition (e.g. 478).

Field situation regarding the time of death is not addressed in the Application (e.g. 478).

The specific cellular interactions of rabbit calicivirus with host cells (e.g. 768).

The pathogenesis of RCD (e.g. 478).

Further research on transmission, persistence, and mortality rates of RCD in the field (e.g. 356).

6.3.2 IMMUNOGENICITY

A few submissions addressed matters related to immunogenicity. The majority of these submissions were from persons or organisations that were opposed to the introduction of RCD.

Issues

The main areas of concern were:

  • the effects of immunity on rabbit populations; and
  • the types of antibodies and the role of other components of the immune system.

Most submissions addressing these matters, including a supporter of introduction (711) and several whose stance was unclear, focussed their attention on the possibility of a younger cohort of the rabbit population becoming immune to RCD. They observed that the virus appeared to be only a short-term solution; with the initial high mortality of rabbits being followed by an eventual return to high levels of rabbit infestation as the entire population developed immunity.

One submitter (478) noted that the types of antibodies produced and the role of other components of the immune system were neither investigated in the Application nor in the published literature on the rabbit calicivirus.

Matters which submitters suggest should be addressed or require further information:

A study of the presence or otherwise of RCD antibodies in the rabbit populations of New Zealand (e.g. 343).

6.3.3 SPREAD OF THE DISEASE

More submissions addressed the characteristics of the virus with respect to epidemiology than was the case for each of the other three topics in this section. Most of the submissions on this topic were again from organisations or individuals who opposed the importation of RCD.

Issues

The main areas of concern were:

  • the expected behaviour of the disease in New Zealand;
  • the behaviour of the disease in other countries;
  • the lack of parameters or patterns for the spread of the disease under field conditions; and
  • the uncertainty about the spread of the disease.

Expected behaviour in New Zealand

A submitter (413) in favour of introducing RCD maintains that it will spread by close rabbit to rabbit contact; thereby being most effective among high-density populations. Some opponents, however, expressed concern that it will not be confined to an isolated pocket of the South Island, and may spread to other parts of the country. One of them, moreover, remarked that "there will be no putting it back in its box and saying sorry we made a mistake" (308). Others were concerned that RCD would spread to indigenous fauna, livestock, and humans. Another submitter (478) referred to the predictions made about the spread of the rabbit calicivirus in New Zealand on p.45 of the Application, and stated that they must be considered speculative given the little knowledge currently available about the epidemiology of RCD.

Behaviour in other countries

Many submissions discussed the behaviour of RCD in other countries. While a supporter of introducing RCD (763) stated that overseas experience assured us that there would be no problems here, some opponents drew upon the experience of other countries to emphasise the unpredictability and uncontrollable nature of the virus's behaviour. Other submissions, including a qualified supporter of introduction (175), added that environmental differences between New Zealand and other countries, particularly Australia, precluded any accurate assessment of its possible behaviour here.

Conditions influencing spread

Other concerns raised in the submissions focussed more on the specific patterns and conditions for the spread of the RCD. One group of submitters discussed the lack of parameters or patterns for the spread of the disease under field conditions. Some of them highlighted matters such as the paucity of monitoring on field persistence and methods of transmission, the lack of data about pre and post RCD numbers, and the little published information about the pattern of the disease. A submission (478), addressing the factors and conditions of spread as discussed in the Application, pointed out that the effects of climate and seasonal change are unknown at present.

A further set of submissions voiced concerns about the uncertainties associated with the process of spreading RCD. Some called for a cautious approach to its introduction because of its perceived uncontrollability and unpredictability.

Matters which submitters suggest should be addressed or require further information:

The rate of spread, both within and between populations; the rates of mortality within rabbit populations; the rate at which rabbit populations increase after disease outbreaks; and the time intervals between disease outbreaks (e.g. 258).

The likely behaviour of RCD if released in New Zealand and its likely effects in reducing rabbit numbers over a range of habitats (e.g. 487).

The manner in which the virus spreads (e.g. 20, 458).

Proposes chapter three of the Application should conclude with these sentences: "RCD is highly transmissable, both between rabbits and locations. Since exactly how the virus transmitts between rabbits in the field is not well understood, the uncertainties make the planned introduction not viable at this stage." (e.g. 366).

The Application does not show how the disease will spread (e.g. 229).

Table 3.1 on p.45 of the Application should include the information on the ability of named organisms to spread via the gastro intestine (e.g. 722).

The behaviour of rabbit calici under New Zealand conditions compared with Australia (e.g. 768).

The full range of routes of infection in other species (e.g. aerosol, enteric) (e.g. 768).

The problem of the remaining 20% of uninfected rabbits after the initial release of RCD (e.g. 592).

METHODS OF TRANSMISSION

A small number of submissions discussed issues about vectors and the methods of transmission. Most of the comments on this topic came from persons or organisations which opposed the introduction of RCD.

Issues

The main areas of concern were:

  • the vectors; and
  • the methods of transmission.

Vectors

Submitters who took a variety of stances regarding the introduction of the virus contributed to the debate about vectors. One supporter (666) took the view that the high incidence of flies and insects around rabbit burrows would benefit the spread of RCD, while another (413) maintained that no vector link had been established. Other supporters had reservations about the present state of knowledge regarding vectors. Many submissions that opposed the release of the virus were also concerned about a lack of scientific information on this subject; and some speculated about the nature of possible vectors (e.g. birds, mosquitoes, blowflies etc.).

Methods of transmission

Concern about the lack of scientific knowledge was also the dominant theme of submissions which discussed the methods of transmission. One submitter (391), for instance, disputes the possibility of rabbits conveying the virus from China to Spain in four years, and proposes an alternative scenario in which "an endemic host, such as a bird, travelling while asymptomatically excreting the virus, brought the virus to its epizootic host, the rabbit". While another submitter (478) notes that "many of the potential transmission methods are not proven in the field and their roles in the epidemiology of RCD are unknown".

Matters which submitters suggest should be addressed or require further information:

More knowledge about the methods/mechanisms of transmission of RCD (e.g. 135, 176, 242).

The method of transmission and vector have not been clearly identified in the Application (e.g. 601).

There is no mention in the Application of whether the 'transmission medium' was infected (e.g. 391).

Information about vectors specific to New Zealand (e.g. 790).

Testing of marine species in Australia or New Zealand (e.g. 755).

A better knowledge of the mechanism of transmission and cross-species susceptibility is required for risk factors to be properly evaluated (e.g. 176).

The possible role of arthropods as a means of transmission (e.g. 609).

The role of other species as intermediate hosts or reservoirs of RCD (e.g. 768).

The vectors of RCD/RHCD have not been identified in the terrestrial and marine environments (e.g. 755).

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