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Abstract Several conventional and recently available tools are available for an integrated control of European rabbits in Australia. We quantified the impact of the release of rabbit haemorrhagic disease virus K5 (RHDV K5, hereafter K5) and pindone (2‐pivalyl‐1,3‐indandione) baiting at 13 sites within Cudlee Creek fire scar in the Adelaide Hills, South Australia. K5 release was followed by pindone baiting between December 2021 and March 2022; the application of both control methods followed industry best practice. We counted rabbits using spotlights before and after the application of both control methods. Fly samples and livers from dead rabbits were collected to track K5 transmission within and between sites, and to detect the natural circulation of rabbit haemorrhagic disease virus 2 (RHDV2). K5 release had minimal impact on rabbit populations, with treated populations increasing by a mean of 65.5% at 14 days post‐release and 27.9% at 77 days post‐K5 release across all sites, comparable to the changes at control sites. K5 detection in flies up to 77 days post its release, and its detection in rabbit livers, demonstrates that it can survive and transmit in the environment for prolonged periods and that it can lethally infect some rabbits. This limited impact of K5 is consistent with previous studies and may be explained by pre‐existing RHDV/RHDV2 immunity in the target populations or the presence of young rabbits with natural innate RHDV immunity. The detection of K5 in flies from control sites demonstrates that it was vectored beyond its release location. A reduction in rabbit counts post‐pindone baiting was observed at most treatment sites, with a mean population reduction of 36.6% across all sites. Landholders need to carefully and strategically plan their integrated rabbit control programmes. Not all combinations of controls, even if theoretically logical, achieve meaningful outcomes for rabbit management.

Australia has multiple lagoviruses with differing pathogenicity. The circulation of these viruses was traditionally determined through opportunistic sampling events. In the lead up to the nationwide release of RHDVa-K5 (GI.1aP-GI.1a) in 2017, an existing citizen science program, RabbitScan, was augmented to allow members of the public to submit samples collected from dead leporids for lagovirus testing. This study describes the information obtained from the increased number of leporid samples received between 2015 and 2022 and focuses on the recent epidemiological interactions and evolutionary trajectory of circulating lagoviruses in Australia between October 2020 and December 2022. A total of 2771 samples were tested from January 2015 to December 2022, of which 1643 were lagovirus-positive. Notable changes in the distribution of lagovirus variants were observed, predominantly in Western Australia, where RHDV2-4c (GI.4cP-GI.2) was detected again in 2021 after initially being reported to be present in 2018. Interestingly, we found evidence that the deliberately released RHDVa-K5 was able to establish and circulate in wild rabbit populations in WA. Overall, the incorporation of citizen science approaches proved to be a cost-efficient method to increase the sampling area and enable an in-depth analysis of lagovirus distribution, genetic diversity, and interactions. The maintenance of such programs is essential to enable continued investigations of the critical parameters affecting the biocontrol of feral rabbit populations in Australia, as well as to enable the detection of any potential future incursions.

Rabbit haemorrhagic disease virus (RHDV) is established as a landscape-scale biocontrol that assists the management of invasive European rabbits and their impacts in both Australia and New Zealand. In addition to this, it is also available to land managers to augment rabbit control efforts at a local scale. However, current methods of deploying RHDV to rabbits that rely on the consumption of virus-treated baits can be problematic as rabbits are reluctant to consume bait when there is abundant, green, protein-rich feed available. We ran a suite of interrupted time-series experiments to compare the duration of infectivity of two conventional (carrot and oat baits) and two novel (meat bait and soil burrow spray) methods of deploying RHDV to rabbits. All methods effectively killed exposed rabbits. Soil burrow spray and carrot baits resulted in infection and mortality out to 5 days post their deployment in the field, and meat baits caused infection out to 10 days post their deployment. In contrast, oat baits continued to infect and kill exposed rabbits out to 20 days post deployment. Molecular assays demonstrated high viral loads in deployed baits beyond the duration for which they were infectious or lethal to rabbits. Based on our results, we suggest that the drying of meat baits may create a barrier to effective transmission of RHDV by adult flies within 10 days. We therefore hypothesise that fly larvae production and development on infected tissues is critical to prolonged viral transmission from meat baits, and similarly from carcasses of RHDV mortalities, via mechanical fly vectors. Our study demonstrates that meat baits and soil spray could provide additional virus deployment options that remove the need for rabbits to consume baits at times when they are reluctant to do so.

Following the arrival of rabbit haemorrhagic disease virus 2 (RHDV2) in Australia, average rabbit population abundances were reduced by 60% between 2014 and 2018 based on monitoring data acquired from 18 sites across Australia. During this period, as the seropositivity to RHDV2 increased, concurrent decreases were observed in the seroprevalence of both the previously circulating RHDV1 and RCVA, a benign endemic rabbit calicivirus. However, the detection of substantial RHDV1 seropositivity in juvenile rabbits suggested that infections were continuing to occur, ruling out the rapid extinction of this variant. Here we investigate whether the co-circulation of two pathogenic RHDV variants was sustained after 2018 and whether the initially observed impact on rabbit abundance was still maintained. We monitored rabbit abundance and seropositivity to RHDV2, RHDV1 and RCVA at six of the initial eighteen sites until the summer of 2022. We observed sustained suppression of rabbit abundance at five of the six sites, with the average population reduction across all six sites being 64%. Across all sites, average RHDV2 seroprevalence remained high, reaching 60–70% in adult rabbits and 30–40% in juvenile rabbits. In contrast, average RHDV1 seroprevalence declined to

Several conventional and recently available tools are available for an integrated control of European rabbits in Australia. We quantified the impact of the release of rabbit haemorrhagic disease virus K5 (RHDV K5, hereafter K5) and pindone (2‐pivalyl‐1,3‐indandione) baiting at 13 sites within Cudlee Creek fire scar in the Adelaide Hills, South Australia. K5 release was followed by pindone baiting between December 2021 and March 2022; the application of both control methods followed industry best practice. We counted rabbits using spotlights before and after the application of both control methods. Fly samples and livers from dead rabbits were collected to track K5 transmission within and between sites, and to detect the natural circulation of rabbit haemorrhagic disease virus 2 (RHDV2). K5 release had minimal impact on rabbit populations, with treated populations increasing by a mean of 65.5% at 14 days post‐release and 27.9% at 77 days post‐K5 release across all sites, comparable to the changes at control sites. K5 detection in flies up to 77 days post its release, and its detection in rabbit livers, demonstrates that it can survive and transmit in the environment for prolonged periods and that it can lethally infect some rabbits. This limited impact of K5 is consistent with previous studies and may be explained by pre‐existing RHDV/RHDV2 immunity in the target populations or the presence of young rabbits with natural innate RHDV immunity. The detection of K5 in flies from control sites demonstrates that it was vectored beyond its release location. A reduction in rabbit counts post‐pindone baiting was observed at most treatment sites, with a mean population reduction of 36.6% across all sites. Landholders need to carefully and strategically plan their integrated rabbit control programmes. Not all combinations of controls, even if theoretically logical, achieve meaningful outcomes for rabbit management. [ABSTRACT FROM AUTHOR]

Australia has multiple lagoviruses with differing pathogenicity. The circulation of these viruses was traditionally determined through opportunistic sampling events. In the lead up to the nationwide release of RHDVa-K5 (GI.1aP-GI.1a) in 2017, an existing citizen science program, RabbitScan, was augmented to allow members of the public to submit samples collected from dead leporids for lagovirus testing. This study describes the information obtained from the increased number of leporid samples received between 2015 and 2022 and focuses on the recent epidemiological interactions and evolutionary trajectory of circulating lagoviruses in Australia between October 2020 and December 2022. A total of 2771 samples were tested from January 2015 to December 2022, of which 1643 were lagovirus-positive. Notable changes in the distribution of lagovirus variants were observed, predominantly in Western Australia, where RHDV2-4c (GI.4cP-GI.2) was detected again in 2021 after initially being reported to be present in 2018. Interestingly, we found evidence that the deliberately released RHDVa-K5 was able to establish and circulate in wild rabbit populations in WA. Overall, the incorporation of citizen science approaches proved to be a cost-efficient method to increase the sampling area and enable an in-depth analysis of lagovirus distribution, genetic diversity, and interactions. The maintenance of such programs is essential to enable continued investigations of the critical parameters affecting the biocontrol of feral rabbit populations in Australia, as well as to enable the detection of any potential future incursions. [ABSTRACT FROM AUTHOR]

Rabbit haemorrhagic disease virus (RHDV) is established as a landscape-scale biocontrol that assists the management of invasive European rabbits and their impacts in both Australia and New Zealand. In addition to this, it is also available to land managers to augment rabbit control efforts at a local scale. However, current methods of deploying RHDV to rabbits that rely on the consumption of virus-treated baits can be problematic as rabbits are reluctant to consume bait when there is abundant, green, protein-rich feed available. We ran a suite of interrupted time-series experiments to compare the duration of infectivity of two conventional (carrot and oat baits) and two novel (meat bait and soil burrow spray) methods of deploying RHDV to rabbits. All methods effectively killed exposed rabbits. Soil burrow spray and carrot baits resulted in infection and mortality out to 5 days post their deployment in the field, and meat baits caused infection out to 10 days post their deployment. In contrast, oat baits continued to infect and kill exposed rabbits out to 20 days post deployment. Molecular assays demonstrated high viral loads in deployed baits beyond the duration for which they were infectious or lethal to rabbits. Based on our results, we suggest that the drying of meat baits may create a barrier to effective transmission of RHDV by adult flies within 10 days. We therefore hypothesise that fly larvae production and development on infected tissues is critical to prolonged viral transmission from meat baits, and similarly from carcasses of RHDV mortalities, via mechanical fly vectors. Our study demonstrates that meat baits and soil spray could provide additional virus deployment options that remove the need for rabbits to consume baits at times when they are reluctant to do so. [ABSTRACT FROM AUTHOR]

Following the arrival of rabbit haemorrhagic disease virus 2 (RHDV2) in Australia, average rabbit population abundances were reduced by 60% between 2014 and 2018 based on monitoring data acquired from 18 sites across Australia. During this period, as the seropositivity to RHDV2 increased, concurrent decreases were observed in the seroprevalence of both the previously circulating RHDV1 and RCVA, a benign endemic rabbit calicivirus. However, the detection of substantial RHDV1 seropositivity in juvenile rabbits suggested that infections were continuing to occur, ruling out the rapid extinction of this variant. Here we investigate whether the co-circulation of two pathogenic RHDV variants was sustained after 2018 and whether the initially observed impact on rabbit abundance was still maintained. We monitored rabbit abundance and seropositivity to RHDV2, RHDV1 and RCVA at six of the initial eighteen sites until the summer of 2022. We observed sustained suppression of rabbit abundance at five of the six sites, with the average population reduction across all six sites being 64%. Across all sites, average RHDV2 seroprevalence remained high, reaching 60–70% in adult rabbits and 30–40% in juvenile rabbits. In contrast, average RHDV1 seroprevalence declined to <3% in adult rabbits and 5–6% in juvenile rabbits. Although seropositivity continued to be detected in a low number of juvenile rabbits, it is unlikely that RHDV1 strains now play a major role in the regulation of rabbit abundance. In contrast, RCVA seropositivity appears to be reaching an equilibrium with that of RHDV2, with RCVA seroprevalence in the preceding quarter having a strong negative effect on RHDV2 seroprevalence and vice versa, suggesting ongoing co-circulation of these variants. These findings highlight the complex interactions between different calicivirus variants in free-living rabbit populations and demonstrate the changes in interactions over the course of the RHDV2 epizootic as it has moved towards endemicity. While it is encouraging from an Australian perspective to see sustained suppression of rabbit populations in the eight years following the arrival of RHDV2, it is likely that rabbit populations will eventually recover, as has been observed with previous rabbit pathogens. [ABSTRACT FROM AUTHOR]

Rabbit haemorrhagic disease virus 2 (RHDV2) is now the dominant calicivirus circulating in wild rabbit populations in Australia. This study compared the infection and case fatality rates of RHDV2 and two RHDVs in wild rabbits, as well as their ability to overcome immunity to the respective other strains. Wild rabbits were allocated to groups either blindly or based on pre‐screening for RHDV/RHDV2 antibodies at capture. Rabbits were monitored regularly until their death or humane killing at 7 days post infection. Liver and eyeball samples were collected for lagovirus testing and aging rabbits, respectively. At capture, rabbits showed high seroprevalence to RHDV2 but not to RHDV. In RHDV/RHDV2 seronegative rabbits at capture, infection rates were highest in those inoculated with RHDV2 (81.8%, 18 out of 22), followed by K5 (53.8%, seven out of 13) and CZECH (40.0%, two out of five), but these differences were not statistically significant. In rabbits with previous exposure to RHDV2 at capture, infection rates were highest when inoculated with K5 (59.6%, 31 out of 52) followed by CZECH (46.0%, 23 out of 50), with infection rates higher in younger rabbits for both viruses. In RHDV/RHDV2 seronegative rabbits at capture, case fatality rates were highest for those inoculated with K5 (71.4%), followed by RHDV2 (50.0%) and CZECH (50.0%). In rabbits with previous exposure to RHDV2 at capture, case fatality rates were highest in rabbits inoculated with K5 (12.9%) followed by CZECH (8.7%), with no case fatalities following RHDV2 inoculation. Case fatality rates did not differ significantly between inoculums in either serostatus group at capture. Based on multivariable modelling, time to death post RHDV inoculation increased in rabbits with recent RHDV2 exposure compared with seronegative rabbits and with age. The results suggest that RHDV2 may cause higher mortalities than other variants in seronegative rabbit populations but that K5 may be more effective in reducing rabbit populations in an RHDV2‐dominant landscape. [ABSTRACT FROM AUTHOR]