Arthur Rylah Institute, Department of Energy, Environment and Climate Action, Heidelberg, VIC 3083, Australia.
Biosecurity, Department of Primary Industries and Regions (PIRSA), Urrbrae, SA 5064, Australia.
Viruses. 2023 May 12;15(5):1159. doi: 10.3390/v15051159.
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.
继兔出血症病毒 2 型（RHDV2）传入澳大利亚后，2014 年至 2018 年间，根据澳大利亚 18 个地点的监测数据，兔群数量平均减少了 60%。在此期间，随着 RHDV2 的血清阳性率增加，先前循环的 RHDV1 和 RCVA（一种良性地方性兔杯状病毒）的血清阳性率也同时下降。然而，在幼年兔中检测到大量的 RHDV1 血清阳性，表明感染仍在继续，排除了这种变异迅速灭绝的可能性。在这里，我们研究了 2018 年后两种致病性 RHDV 变异体是否仍持续循环，以及最初观察到的对兔群数量的影响是否仍在维持。我们在最初的 18 个地点中的 6 个地点监测了兔群数量和 RHDV2、RHDV1 和 RCVA 的血清阳性率，直到 2022 年夏季。我们观察到 6 个地点中的 5 个地点持续抑制了兔群数量，所有 6 个地点的平均种群减少率为 64%。在所有地点，RHDV2 的平均血清阳性率仍然很高，成年兔达到 60-70%，幼年兔达到 30-40%。相比之下，成年兔的平均 RHDV1 血清阳性率下降到<3%，幼年兔为 5-6%。尽管仍有少量幼年兔检测到血清阳性，但 RHDV1 株现在不太可能在调节兔群数量方面发挥主要作用。相比之下，RCVA 的血清阳性率似乎与 RHDV2 达到平衡，上一季度的 RCVA 血清阳性率对 RHDV2 血清阳性率有强烈的负面影响，反之亦然，表明这些变异体仍在持续循环。这些发现突出了自由生活兔群中不同杯状病毒变异体之间的复杂相互作用，并表明在 RHDV2 爆发期间，随着其向地方性疾病转变，相互作用的变化。从澳大利亚的角度来看，看到 RHDV2 传入后的 8 年内兔群数量持续减少是令人鼓舞的，但随着先前兔病原体的观察，兔群数量可能最终会恢复。
