Rabbit biocontrol has had dramatic and widespread benefits to Australian agriculture and environment for 60 years, with benefits estimated at over $70 billion. For 20 years only one type of virulent RHDV has been circulating in Australia, to which some populations of rabbits started to develop genetic resistance. Since 2014, with the detection of two exotic virulent RHDVs, and the coordinated release of the RHDV1 K5 strain, there are now four virulent strains of RHDV present in Australia’s rabbit population. This increasing genetic diversity poses challenges as well as opportunities.
Unfortunately, there is never likely to be a silver bullet in rabbit management. We know from monitoring studies that the best response is an ongoing one, ensuring that new rabbit biocontrol agents can be released on a regular basis to counteract reduced effectiveness of existing agents due to increasing immunity and genetic resistance. In addition, boosts to existing controls add to their effectiveness, particularly through a horses-for-courses type approach. As such, rabbit management is not about one-off applications of solutions but regular, community-based approaches drawing from a pipeline of new, existing and evolving solutions.
Note: If you are a vet or domestic rabbit pet owner you can now submit samples directly for testing via this CSIRO portal – https://research.csiro.au/rhdv/ (follow the prompts)
February 2020 update:
While RHDV2 remains the dominant virus circulating in the field in all areas of Australia, several cases of RHDV1 K5 have been detected one location that were not associated with a targeted release. These results suggest that RHDV1 K5 may have become established in wild rabbit populations in some locations. Further monitoring will be carried out through the project to better understand if this has occurred more widely or remains the exception.
CSIRO has developed a new assay for high throughput screening of recombinant caliciviruses. This assay has now been adopted into the routine testing protocols for RabbitScan and has retrospectively been applied to all positive calicivirus samples to confirm the identity of each sample.
A pilot study investigating the suitability of using carrion feeding flies as a better broad scale tool to monitor disease activity at a landscape scale is nearing completion of its first year. Preliminary analysis of the first nine months of samples (March 2019 to January 2020) indicate that RHDV activity can indeed be detected in fly samples, but the sensitivity of this method remains unclear at this stage. The aim is to continue this study for an additional 12 months to get a better understanding of this tool to monitor RHDV activity at a wider scale.
August 2019 update:
Ongoing testing of tissue from deceased rabbits shows RHDV2 remains the dominant rabbit calicivirus circulating in Australia, with K5 detected at release sites. A new screening method is being implemented to detect recombinant viruses.
Rabbit monitoring at selected intensive sites in TAS, ACT, WA, NSW and SA is ongoing or ramping up shortly, with a minimum bi-annual sampling taking place. In addition, monitoring and sampling of the rabbit population at the Turretfield research site continues as part of this project, building on extensive knowledge of this wild rabbit population and adding these ongoing monitoring results to the long-term RHDV and myxoma disease database at this site.
A paper on optimising and validating molecular testing of carrion flies for rabbit calicivirus detection, including associated protocols was published. This provided the basis for a nationwide year-long pilot study now underway.
February 2019 update:
Intensive rabbit monitoring sites have been established with monitoring well underway at sites in South Australia and the ACT, and due to commence at other sites in Autumn 2019. Sites in South Australia are reporting the lowest abundance of rabbits in more than 20 years, indicating that circulating strains of RHDV are suppressing rabbit numbers.
The methods for sampling, processing and analysing carrion feeding flies for the presence of RHDV have been developed and validated. A national fly monitoring network at over 30 sites across Australia has been established and fortnightly sampling has commenced.
Analysis of samples from dead rabbits submitted directly to CSIRO and through RabbitScan is ongoing – over 1600 samples have been analysed since the beginning of the previous IA-CRC project RHD Boost Rollout, and ~1000 since the K5 release).
Cox, T. E., Ramsey, D. S., Sawyers, E., Campbell, S., Matthews, J., & Elsworth, P. (2019). The impact of RHDV-K5 on rabbit populations in Australia: an evaluation of citizen science surveys to monitor rabbit abundance. Scientific reports, 9(1), 1-11. https://doi.org/10.1038/s41598-019-51847-w
Hall, R. N., Huang, N., Roberts, J., & Strive, T. (2019). Carrion flies as sentinels for monitoring lagovirus activity in Australia. Transboundary and emerging diseases, 66(5), 2025-2032. https://doi.org/10.1111/tbed.13250
Strive, T., Piper, M., Huang, N., Mourant, R., Kovaliski, J., Capucci, L., … & Smith, I. (2019). Retrospective serological analysis reveals presence of the emerging lagovirus RHDV2 in Australia in wild rabbits at least five months prior to its first detection. Transboundary and emerging diseases. https://doi.org/10.1111/tbed.13403
Strive, T., & Cox, T. E. (2019). Lethal biological control of rabbits–the most powerful tools for landscape-scale mitigation of rabbit impacts in Australia. Australian Zoologist, 40(1), 118-128. https://doi.org/10.7882/AZ.2019.016
Ramsey, D. S., Cox, T., Strive, T., Forsyth, D. M., Stuart, I., Hall, R., … & Campbell, S. Emerging RHDV2 suppresses the impact of endemic and novel strains of RHDV on wild rabbit populations. Journal of Applied Ecology. https://doi.org/10.1111/1365-2664.13548