Sustained Impact of RHDV2 on Wild Rabbit Populations across Australia Eight Years after Its Initial Detection

Epitope mapping of a neutralizing antibody against rabbit hemorrhagic disease virus GI.2

In 2010, rabbit hemorrhagic disease virus (RHDV) GI.2 emerged, and unlike RHDV GI.1, it caused mortality in young rabbits, while existing vaccines were not fully protective. The GI.2-specific monoclonal antibody (mAb) 2D9 has been used as a tool to discriminate between these viruses in diagnostic tests. In this study, we mapped the binding epitope for 2D9 on the GI.2 The VP60 capsid protein demonstrated the neutralizing capacity of this mAb, which was able to prevent GI.2 infections in an experimental challenge. Our results suggest that external loops (1, 4 and 5) in the P2 subdomain of VP60 contribute to the discontinuous neutralizing epitope recognized by mAb 2D9. Moreover, analysis of naturally occurring RHDV GI.2 isolates revealed key residues involved in mAb 2D9 binding that are under selective pressure. The findings described in this work provide valuable information regarding our understanding of virus neutralization and immune escape, which may help in the development of novel antiviral compounds.

Evaluation of dried blood spots for serological surveys of myxoma and rabbit hemorrhagic disease viruses in their wild reservoir

Myxoma (MYXV) and rabbit hemorrhagic disease (RHDV) viruses are pathogens of economic relevance for cuniculture and conservation concern for wild European rabbits (Oryctolagus cuniculus), recently classified as 'Endangered' in its native range. Large-scale serological surveys, facilitated by sample collection using dried blood spots (DBS), allow monitoring seroprevalence in the wild reservoir but require evaluating the technique for the host and pathogen of interest. This study aimed to evaluate Protein Saver 903 DBS for MYXV and RHDV (genotype GI.2) serological surveys in European rabbits. Paired serum and DBS collected from 172 rabbits harvested or found dead in the Iberian Peninsula were tested for IgG antibodies specific against MYXV and RHDV GI.2 using indirect ELISA. We found an almost perfect agreement between serum and DBS for MYXV (Cohen's κ=0.914, CI95 0.847 - 0.981) and a strong agreement for RHDV GI.2 (Cohen's κ=0.808, CI95=0.722 - 0.893). The diagnostic sensitivity of DBS was 95.4 % (CI95 90.3 - 97.9 %) for MYXV and 82.1 % (CI95 73.2 - 88.5 %) for RHDV GI.2. The diagnostic specificity and positive predictive value were 100 % for both pathogens. This study supports DBS as a suitable sampling strategy for serological surveys of antibodies specific to MYXV and RHDV GI.2 in European rabbits, which generally agrees with results from other hosts and pathogens where this technique was evaluated.

Rabbit hemorrhagic disease virus 2, 2010-2023: a review of global detections and affected species

Rabbit hemorrhagic disease virus 2/genotype GI.2 (RHDV2/GI.2; Caliciviridae, Lagovirus) causes a highly contagious disease with hepatic necrosis and disseminated intravascular coagulation in several Leporidae species. RHDV2 was first detected in European rabbits (Oryctolagus cuniculus) in France in 2010 and has since spread widely. We gather here data on viral detections reported in various countries and affected species, and discuss pathology, genetic differences, and novel diagnostic aspects. RHDV2 has been detected almost globally, with cases reported in Europe, Africa, Oceania, Asia, and North America as of 2023. Since 2020, large scale outbreaks have occurred in the United States and Mexico and, at the same time, cases have been reported for the first time in previously unaffected countries, such as China, Japan, Singapore, and South Africa, among others. Detections have been notified in domestic and wild European rabbits, hares and jackrabbits (Lepus spp.), several species of cottontail and brush rabbits (Sylvilagus spp.), pygmy rabbits (Brachylagus idahoensis), and red rock rabbits (Pronolagus spp.). RHDV2 has also been detected in a few non-lagomorph species. Detection of RHDV2 causing RHD in Sylvilagus spp. and Leporidae species other than those in the genera Oryctolagus and Lepus is very novel. The global spread of this fast-evolving RNA virus into previously unexploited geographic areas increases the likelihood of host range expansion as new species are exposed; animals may also be infected by nonpathogenic caliciviruses that are disseminated by almost all species, and with which genetic recombination may occur.

Epidemiological characterization and risk assessment of rabbit haemorrhagic disease virus 2 (RHDV2/b/GI.2) in the world

A novel variant of rabbit haemorrhagic disease virus, designated RHDV2/b/GI.2, was first discovered in France in 2010. Subsequently, RHDV2 rapidly spread to Africa, North America, Australia, and Asia. RHDV2 outbreaks have resulted in significant economic losses in the global rabbit industry and disrupted the balance of natural ecosystems. Our study investigated the seasonal characteristics of RHDV2 outbreaks using seasonal indices. RHDV2 is prone to causing significant outbreaks within domestic and wild rabbit populations during the spring season and is more likely to induce outbreaks within wild rabbit populations during late autumn in the Southern Hemisphere. Furthermore, based on outbreak data for domestic and wild rabbits and environmental variables, our study established two MaxEnt models to explore the relationship between RHDV2 outbreaks and the environmental factors and conducted outbreak risk predictions for RHDV2 in global domestic and wild rabbit populations. Both models demonstrated good predictive performance, with AUC values of 0.960 and 0.974, respectively. Road density, isothermality, and population density were identified as important variables in the outbreak of RHDV2 in domestic rabbits, while road density, normalized difference vegetation index, and mean annual solar radiation were considered key variables in the outbreak of RHDV2 in wild rabbits. The environmental factors associated with RHDV2 outbreaks identified in our study and the outbreak risk prediction maps generated in our study will aid in the formulation of appropriate RHDV2 control measures to reduce the risk of morbidity in domestic and wild rabbits.

First Detection of Benign Rabbit Caliciviruses in Chile

Pathogenic lagoviruses (Rabbit hemorrhagic disease virus, RHDV) are widely spread across the world and are used in Australia and New Zealand to control populations of feral European rabbits. The spread of the non-pathogenic lagoviruses, e.g., rabbit calicivirus (RCV), is less well studied as the infection results in no clinical signs. Nonetheless, RCV has important implications for the spread of RHDV and rabbit biocontrol as it can provide varying levels of cross-protection against fatal infection with pathogenic lagoviruses. In Chile, where European rabbits are also an introduced species, myxoma virus was used for localised biocontrol of rabbits in the 1950s. To date, there have been no studies investigating the presence of lagoviruses in the Chilean feral rabbit population. In this study, liver and duodenum rabbit samples from central Chile were tested for the presence of lagoviruses and positive samples were subject to whole RNA sequencing and subsequent data analysis. Phylogenetic analysis revealed a novel RCV variant in duodenal samples that likely originated from European RCVs. Sequencing analysis also detected the presence of a rabbit astrovirus in one of the lagovirus-positive samples.

Utilizing Molecular Epidemiology and Citizen Science for the Surveillance of Lagoviruses in Australia

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.