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Liu J, Fordham DA, Cooke BD, Cox T, Mutze G, Strive T. Distribution and prevalence of the Australian non-pathogenic rabbit calicivirus is correlated with rainfall and temperature. PLoS One 2014; 9:e113976. [PMID: 25486092 PMCID: PMC4259302 DOI: 10.1371/journal.pone.0113976] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Accepted: 11/02/2014] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Australia relies heavily on rabbit haemorrhagic disease virus (RHDV) for the biological control of introduced European wild rabbits Oryctolagus cuniculus, which are significant economic and environmental pests. An endemic non-pathogenic rabbit calicivirus termed RCV-A1 also occurs in wild rabbits in Australian and provides partial protection against lethal RHDV infection, thus interfering with effective rabbit control. Despite its obvious importance for rabbit population management, little is known about the epidemiology of this benign rabbit calicivirus. METHODS We determined the continent-wide distribution and prevalence of RCV-A1 by analysing 1,805 serum samples from wild rabbit populations at 78 sites across Australia for the presence of antibodies to RCV-A1 using a serological test that specifically detects RCV-A1 antibodies and does not cross-react with co-occurring RHDV antibodies. We also investigated possible correlation between climate variables and prevalence of RCV-A1 by using generalised linear mixed effect models. RESULTS Antibodies to RCV-A1 were predominantly detected in rabbit populations in cool, high rainfall areas of the south-east and south-west of the continent. There was strong support for modelling RCV-A1 prevalence as a function of average annual rainfall and minimum temperature. The best ranked model explained 26% of the model structural deviance. According to this model, distribution and prevalence of RCV-A1 is positively correlated with periods of above average rainfall and negatively correlated with periods of drought. IMPLICATIONS Our statistical model of RCV-A1 prevalence will greatly increase our understanding of RCV-A1 epidemiology and its interaction with RHDV in Australia. By defining the environmental conditions associated with the prevalence of RCV-A1, it also contributes towards understanding the distribution of similar viruses in New Zealand and Europe.
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Affiliation(s)
- June Liu
- Commonwealth Scientific and Industrial Research Organisation, Ecosystem Sciences Division, Canberra, Australian Capital Territory 2601, Australia
- Invasive Animals Cooperative Research Centre, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
| | - Damien A. Fordham
- The Environment Institute and School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Brian D. Cooke
- Institute of Applied Ecology, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
- Invasive Animals Cooperative Research Centre, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
| | - Tarnya Cox
- Invasive Animals Cooperative Research Centre, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
- Vertebrate Pest Research Unit, NSW Department Primary Industries, Orange, New South Wales 2800, Australia
| | - Greg Mutze
- Natural Resources Management Biosecurity Unit, Department of Water, Land and Biodiversity Conservation, Adelaide, South Australia 5001, Australia
| | - Tanja Strive
- Commonwealth Scientific and Industrial Research Organisation, Ecosystem Sciences Division, Canberra, Australian Capital Territory 2601, Australia
- Invasive Animals Cooperative Research Centre, University of Canberra, Canberra, Australian Capital Territory 2601, Australia
- * E-mail:
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Olsen J, Cooke B, Trost S, Judge D. Is wedge-tailed eagle, Aquila audax, survival and breeding success closely linked to the abundance of European rabbits, Oryctolagus cuniculus? WILDLIFE RESEARCH 2014. [DOI: 10.1071/wr14033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context Some ecologists argue that nesting success and abundance of wedge-tailed eagles (Aquila audax) are strongly linked to the abundance of introduced wild rabbits (Oryctolagus cuniculus). Consequently, concerns were expressed about eagle population viability when the biological control agent rabbit haemorrhagic disease virus (RHDV) heavily reduced rabbit numbers. However, observations following the spread of rabbit haemorrhagic disease (RHD) in Australia and Spain (where Aquila adalberti is an equivalent of A. audax) question this assertion. Eagle numbers did not fall even though rabbits declined regionally by up to 90% in both countries. Aims To reconsider the assumption of a strong link between rabbit abundance and wedge-tailed eagle breeding and population maintenance. Dispelling misconceptions, if any, about the eagles’ dependence on rabbits would benefit the future management of both eagles and rabbits. Methods We reviewed the literature associated with claims that eagles were heavily dependent on rabbits and asked whether these views could be substantiated given the lack of changes in eagle abundance following the spread of RHD. Data on eagle egg-clutch size and nesting success were also reviewed. Conclusions There is little evidence that eagles depend heavily on rabbits as prey. Instead, as rabbits decline, more kangaroos, reptiles and birds are eaten, partly because more native prey becomes available. Eagles have a high proportion of rabbits in their diets mainly where degradation of natural ecosystems, including that caused by rabbits, results in native prey being rare or unavailable. There has been minimal variation in average clutch size following major perturbations in rabbit population size. Implications Rather than perpetuating the idea that high populations of rabbits are needed for wedge-tailed eagle conservation, resources would be better re-directed into understanding continental-scale eagle population dynamics. This would provide a more rational framework to assist decisions on future biological control agents for rabbits.
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Liu J, Kerr PJ, Strive T. A sensitive and specific blocking ELISA for the detection of rabbit calicivirus RCV-A1 antibodies. Virol J 2012; 9:182. [PMID: 22943557 PMCID: PMC3493337 DOI: 10.1186/1743-422x-9-182] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Accepted: 08/28/2012] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Antibodies to non-pathogenic rabbit caliciviruses (RCVs) cross-react in serological tests for rabbit hemorrhagic disease virus (RHDV) and vice versa, making epidemiological studies very difficult where both viruses occur. It is important to understand the distribution and interaction of the two viruses because the highly pathogenic RHDV has been used as a biocontrol agent for wild rabbits in Australia and New Zealand for the past 17 years. The presence of the benign RCV Australia 1 (RCV-A1) is considered a key factor for the failure of RHDV mediated rabbit control in cooler, wetter areas of Australia. RESULTS A highly sensitive and specific blocking ELISA was developed for the detection of RCV-A1 antibodies. When sera from rabbits with a known infection history for either RCV-A1 or RHDV were tested, this assay showed 100% sensitivity and no cross-reactivity with RHDV sera (100% specificity). CONCLUSIONS This new ELISA not only allows the detection of RCV-A1 at a population level, but also permits the serological status of individual rabbits to be determined more reliably than previously described methods. This robust and simple to perform assay is therefore the tool of choice for studying RCV-A1 epidemiology in Australian wild rabbit populations.
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Affiliation(s)
- June Liu
- Commonwealth Scientific and Industrial Research Organisation, Ecosystem Sciences Division, GPO Box 1700, Canberra ACT, 2601, Australia
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Rabbit haemorrhagic disease: are Australian rabbits (Oryctolagus cuniculus) evolving resistance to infection with Czech CAPM 351 RHDV? Epidemiol Infect 2012; 140:1972-81. [PMID: 22244198 DOI: 10.1017/s0950268811002743] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Rabbit haemorrhagic disease is a major tool for the management of introduced, wild rabbits in Australia. However, new evidence suggests that rabbits may be developing resistance to the disease. Rabbits sourced from wild populations in central and southeastern Australia, and domestic rabbits for comparison, were experimentally challenged with a low 60 ID50 oral dose of commercially available Czech CAPM 351 virus - the original strain released in Australia. Levels of resistance to infection were generally higher than for unselected domestic rabbits and also differed (0-73% infection rates) between wild populations. Resistance was lower in populations from cooler, wetter regions and also low in arid regions with the highest resistance seen within zones of moderate rainfall. These findings suggest the external influences of non-pathogenic calicivirus in cooler, wetter areas and poor recruitment in arid populations may influence the development rate of resistance in Australia.
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Le Gall-Reculé G, Zwingelstein F, Fages MP, Bertagnoli S, Gelfi J, Aubineau J, Roobrouck A, Botti G, Lavazza A, Marchandeau S. Characterisation of a non-pathogenic and non-protective infectious rabbit lagovirus related to RHDV. Virology 2010; 410:395-402. [PMID: 21195443 DOI: 10.1016/j.virol.2010.12.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2010] [Revised: 10/03/2010] [Accepted: 12/03/2010] [Indexed: 11/17/2022]
Abstract
The existence of non-pathogenic RHDV strains was established when a non-lethal virus named rabbit calicivirus (RCV) was characterised in 1996 in Italy. Since then, different RNA sequences related to RHDV have been detected in apparently healthy domestic and wild rabbits, and recently a new lagovirus was identified in Australia. We have characterised from seropositive healthy domestic rabbits a non-lethal lagovirus that differs from RHDV in terms of pathogenicity, tissue tropism and capsid protein sequence. Phylogenetic analyses have revealed that it is close to the Ashington strain and to the RCV, but distinct. We proved experimentally that it is infectious but non-pathogenic and demonstrated that, contrary to the other described non-pathogenic lagoviruses, it induces antibodies that do not protect against RHDV. Our results indicate the existence of a gradient of cross-protection between circulating strains, from non-protective, partially protective to protective strains, and highlight the extent of diversity within the genus Lagovirus.
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Affiliation(s)
- Ghislaine Le Gall-Reculé
- French Agency for Food, Environmental and Occupational Health Safety (Anses), Laboratory for Studies and Research on Poultry, Pig and Fish Farming (LERAPP), UVIPAC, BP 53, F-22440 Ploufragan, France.
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Mutze G, Sinclair R, Peacock D, Kovaliski J, Capucci L. Does a benign calicivirus reduce the effectiveness of rabbit haemorrhagic disease virus (RHDV) in Australia? Experimental evidence from field releases of RHDV on bait. WILDLIFE RESEARCH 2010. [DOI: 10.1071/wr09162] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context. European rabbits are serious environmental and agricultural pests throughout their range in Australia. Rabbit haemorrhagic disease virus (RHDV) greatly reduced rabbit numbers in arid central Australia but had less impact in cooler, higher-rainfall areas. RHDV-like benign caliciviruses (bCVs) have been implicated in limiting the impact of RHDV in the higher-rainfall regions of Australia and also in Europe.
Aims. Experimental releases of RHDV on bait were tested as a means of initiating disease outbreaks. Serological evidence of antibodies to bCVs was examined to determine whether they reduce mortality rates and/or spread of the released RHDV, and how that might influence the effectiveness of future RHDV releases for rabbit management.
Methods. Four experimental releases were conducted in high-rainfall and coastal regions of southern Australia. Virus activity was implied from recapture rates and serological changes in marked rabbits, and genetic sequencing of virus recovered from dead rabbits. Changes in rabbit abundance were estimated from spotlight transect counts.
Key results. Release of RHDV on bait produced disease outbreaks that challenged almost all animals within the general release area and spread up to 4 km beyond the release sites. Recapture rates were high in marked rabbits that possessed antibodies from previous exposure to RHDV and extremely low amongst rabbits that lacked any detectable antibodies. Rabbits carrying antibodies classified as being due to previous infection with bCVs had recapture rates that were dependent on circulating antibody titre and were ~55% of recapture rates in rabbits with clear antibodies to RHDV.
Conclusions. This is the first quantified evidence that antibodies produced against bCVs provide significant protection against RHD outbreaks in field populations of rabbits.
Implications. bCVs can greatly reduce the impact of RHDV on wild-rabbit populations in Australia and presumably elsewhere. RHDV can be effectively released on bait although further releases are likely to be of minor or inconsistent benefit for controlling rabbit numbers where bCVs are common.
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McPhee SR, Butler KL, Kovaliski J, Mutze G, Capucci L, Cooke BD. Antibody status and survival of Australian wild rabbits challenged with rabbit haemorrhagic disease virus. WILDLIFE RESEARCH 2009. [DOI: 10.1071/wr08137] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In Australia, the epidemiology of rabbit haemorrhagic disease virus (RHDV) is complicated by non-pathogenic forms of calicivirus (bCV) co-circulating with RHDV and providing variable protection from RHDV. Currently no bCV virus-specific antibody tests exist; however, a series of four ELISAs used to detect antibodies to RHDV provided an indirect means to detect antibodies to bCV, enabling antibody categories of seronegative, maternal RHDV, RHDV or bCV to be determined. Rabbits (188) from four locations were challenged with RHDV and logistic regression models determined that, for rabbits <15 months old, survival was dependent on antibody titres alone and the relationship did not vary with age, capture site, gender, liveweight or reproductive status. All rabbits survived challenge after reaching 15 months of age, irrespective of their antibody titres. Where bCV antibodies were prevalent in young rabbits, the bCV category did not adequately summarise all information about rabbit survival that can be obtained from antibody titres. Within antibody categories, 95% of rabbits with RHDV, 33% with bCV, 40% with maternal RHDV and 22% with seronegative antibodies survived. The high survival rate of adults implies that natural outbreaks or controlled releases of RHDV will have little impact on adult breeding rabbits. Therefore, where RHDV and bCV are endemic, conventional rabbit-control programs targeting the immune breeding populations should provide the most predictable outcome for long-term maintenance of low rabbit populations.
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Strive T, Wright JD, Robinson AJ. Identification and partial characterisation of a new Lagovirus in Australian wild rabbits. Virology 2008; 384:97-105. [PMID: 19049842 DOI: 10.1016/j.virol.2008.11.004] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 09/01/2008] [Accepted: 11/04/2008] [Indexed: 11/25/2022]
Abstract
Rabbit Haemorrhagic Disease Virus (RHDV) is widely used in Australia to control feral rabbit populations. Before RHDV was released on the Australian continent in 1996, antibodies cross-reacting in RHDV specific ELISAs were found in Australian wild rabbits, leading to the hypothesis that a non-pathogenic calicivirus had been circulating in rabbit populations in Australia, potentially providing some level of cross-immunoprotection to RHDV infection. For the detection of this putative virus, a universal lagovirus PCR test was developed to screen a variety of different tissues of wild caught rabbits. We identified a new lagovirus in the intestinal tissues of three apparently healthy young wild rabbits. Quantitative Real Time PCR analysis revealed high concentrations of viral RNA in intestinal tissues and suggests a faecal-oral mode of transmission. Genome organisation and phylogenetic analysis following the sequencing of the entire viral genome revealed a new member of the genus Lagovirus within the family Caliciviridae.
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Affiliation(s)
- T Strive
- Commonwealth Scientific and Industrial Research Organisation, Canberra, Australian Capital Territory, Australia.
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Richardson BJ, Phillips S, Hayes RA, Sindhe S, Cooke BD. Aspects of the biology of the European rabbit (Oryctolagus cuniculus) and rabbit haemorrhagic disease virus (RHDV) in coastal eastern Australia. WILDLIFE RESEARCH 2007. [DOI: 10.1071/wr06117] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A population of wild rabbits in a high-rainfall area near Sydney, New South Wales, was studied for 8 years to investigate the population biology of the rabbit in a high-rainfall area, to examine factors affecting the length of the breeding season, and to describe the biology of RHDV and a RHDV-like virus in the population. The breeding season was short, starting in June and ending in October, though some conceptions occurred in every month of the year. Supplementary feeding with grain, germinated wheat or high-protein rabbit pellets did not extend the breeding season, so predictions that the length of the breeding season and occurrence of anaemia were influenced by a lack of protein in the diet were not upheld. Myxomatosis appeared in late summer each year as in inland southern Australia. Studies of the immunostatus of the population showed that, even in the years before RHDV was released in Australia, 80–100% of adult animals were seropositive when tested with ELISA specifically designed to detect antibodies to RHDV, arguably owing to the presence of a RHDV-like virus. The proportion of seropositive animals fell when annual rainfall was below 600 mm and rose when it was above 700 mm. Presumably, in areas where rainfall is usually low the proportion of the population infected with the putative RHDV-like virus would slowly drop to a low level, providing a possible basis for the different epidemiological patterns found for RHDV in different parts of Australia.
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Bruce JS, Twigg LE. The reintroduction, and subsequent impact, of rabbit haemorrhagic disease virus in a population of wild rabbits in south-western Australia. WILDLIFE RESEARCH 2005. [DOI: 10.1071/wr04025] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The natural arrival of rabbit haemorrhagic disease virus (RHDV) in south-western Australia in September 1996 resulted in a reduction in rabbit numbers of ~65% (~90% morbidity, with ~72% mortality of infected rabbits). As no signs of the disease (clinical or serological) were seen over the next two years, and as rabbit numbers over the last 12-month monitoring period at the site were similar to those observed before the natural 1996 RHDV epizootic (i.e. pre-RHD), RHDV was deliberately reintroduced into this rabbit population in April 1999 (autumn). Seven RHDV-inoculated rabbits were released prior to the main breeding season when <3% of sampled rabbits (n = 118) were seropositive for RHDV antibodies. Following the deliberate release, the overall decline in rabbit numbers (68%) was comparable to that seen during the natural 1996 epizootic. However, on the basis of the observed changes in rabbit numbers, and in their serology, the impact of the deliberate RHDV release appeared to be more variable across the six trapping areas than was seen during the natural 1996 spring epizootic. The reductions in rabbit numbers on these areas 6–8 weeks after RHDV-release ranged from 55% to 90%. The serology of the surviving rabbits on the trapping areas was also variable over this period, with the proportion of seropositive rabbits ranging from 5% to 90%. Overall, only 15% of the surviving rabbit population showed evidence of recent challenge by RHDV, giving a morbidity rate of 73% 8 weeks after the release. However, over 90% of infected rabbits died. This provides further evidence that some rabbits remained un-challenged by RHDV for up to 8 weeks after its release. The variable impact of the April 1999 release may have been partially caused by the observed differences in abundance of insect vectors, and/or an apparent increase in the incidence of non-virulent RHDV in the months preceding the release.
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