First detection of rabbit haemorrhagic disease virus (RHDV2) in Singapore

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.

Diagnosis of a Rabbit Hemorrhagic Disease Virus 2 (RHDV2) and the Humoral Immune Protection Effect of VP60 Vaccine

Rabbit hemorrhagic disease (RHD) is known as rabbit plague and hemorrhagic pneumonia. It is an acute, septic, and highly fatal infectious disease caused by the Lagovirus rabbit hemorrhagic disease virus (RHDV) in the family Caliciviridae that infects wild and domestic rabbits and hares (lagomorphs). At present, RHDV2 has caused huge economic losses to the commercial rabbit trade and led to a decline in the number of wild lagomorphs worldwide. We performed a necropsy and pathological observations on five dead rabbits on a rabbit farm in Tai'an, China. The results were highly similar to the clinical and pathological changes of typical RHD. RHDV2 strain was isolated and identified by RT-PCR, and partial gene sequencing and genetic evolution analysis were carried out. There were significant differences in genetic characteristics and antigenicity between RHDV2 and classical RHDV strain, and the vaccine prepared with the RHDV strain cannot effectively prevent rabbit infection with RHDV2. Therefore, we evaluated the protective efficacy of a novel rabbit hemorrhagic virus baculovirus vector inactivated vaccine (VP60) in clinical application by animal regression experiment. The result showed that VP60 could effectively induce humoral immunity in rabbits. The vaccine itself had no significant effect on the health status of rabbits. This study suggested that the clinical application of VP60 may provide new ideas for preventing the spread of RHD2.

Rabbit haemorrhagic disease virus 2 from Singapore 2020 outbreak revealed an Australian recombinant variant

Rabbit haemorrhagic disease (RHD) is a significant and debilitating viral disease affecting lagomorphs. In September 2020, Singapore reported its first cases of RHD virus (RHDV) infection in domesticated rabbits. The initial findings reported that the outbreak strain belonged to genotype GI.2 (RHDV2/RHDVb), and epidemiological investigations could not identify the definitive source of the virus origin. Further recombination detection and phylogenetic analyses of the Singapore outbreak strain revealed that the RHDV was a GI.2 structural (S)/GI.4 non-structural (NS) recombinant variant. Sequence analyses on the National Centre for Biotechnology Information (NCBI) database showed high homology to recently emerged Australian variants, which were prevalent in local Australian lagomorph populations since 2017. Time-structured and phylogeographic analyses for the S and NS genes revealed a close genetic relationship between the Singapore RHDV strain and the Australian RHDV variants. More thorough epidemiological inquiries are necessary to ascertain how an Australian RHDV was introduced into the Singapore rabbit population, and opportune development of RHDV diagnostics and vaccines will be important to safeguard lagomorphs from future RHDV infection and disease management.

Confirmation of the Rabbit Hemorrhagic Disease Virus Type 2 (GI.2) Circulation in North Africa

Rabbit hemorrhagic disease (RHD) is a highly contagious viral disease that causes fatal acute hepatitis in domestic and wild lagomorphs. It has taken on major economic importance in countries like Morocco. In addition to the classical virus (RHDV), a novel emerged genotype (RHDV2) is circulating, especially in the north shore of the Mediterranean basin since 2010. Many small animal farmers reported clinical cases from several rabbitries in Agadir (Morocco) despite systematic vaccination against the RHDV. The main objective was to characterize the current RHDV strains circulating in the studied area to help to choose an adequate vaccine. For that, we extracted viral RNA from rabbit livers, carried out the PCR analyses, and we sequenced the viral structural capsid protein (VP60) of the RHDV. The phylogenetic analysis results allowed us to state that the novel genotype (RHDV2) is circulating in the studied geographical area, and to characterize the isolated sequences. As a conclusion, we recommend updating RHD epidemiological relating data and reviewing the vaccine protocols by both targeting RHDV (GI.1) and RHDV2 (GI.2) in any future preventive program.

Resolution of rabbit haemorrhagic disease virus 2 (RHDV2; Lagovirus europeus GI.2) outbreak in Singapore

Rabbit haemorrhagic disease (RHD) is a highly contagious viral disease affecting lagomorphs. The first documented cases of RHD in Singapore occurred in adult pet European rabbits in September 2020. Singapore subsequently declared the outbreak resolved in December 2020. Epidemiological investigations ruled out introductions via importation of infected rabbits and contaminated feed. The source could not be definitively determined. However, the findings suggested that the incident involved both inter- and intra-household transmission and veterinary clinic-household transmission. This incident demonstrated the importance of sustained application of biosecurity measures, epidemiological investigations including active case finding, control measures such as expedient vaccine dissemination and risk communications. It showed that even without a wild lagomorph population, an urbanized city-state like Singapore could still encounter emerging diseases such as RHD. Given its social impact on rabbit owners, the National Parks Board, Singapore and private veterinarians worked together to communicate with rabbit owners in order to urge them to adopt biosecurity measures and to address their concerns.