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Rabbit hemorrhagic disease is a highly contagious and acute fatal disease caused by rabbit hemorrhagic disease virus (RHDV). The first outbreak of RHDV2 in 2020 has posed a serious threat to the rabbit breeding industry in China. An effective and specific detection strategy for RHDV GI.1 (RHDV1) and GI.2 (RHDV2) is urgently needed. In this study, we established a reverse transcription loop‐mediated isothermal amplification (RT‐LAMP)‐CRISPR/Cas12a‐based dual readout portable detection platform. The platform showed excellent specificity to identify RHDV1 and RHDV2 strains and no cross‐reaction with other prevalent pathogens of rabbit. The detection limit for RHDV1 and RHDV2 by RT‐LAMP‐CRISPR/Cas12a could reach 10 copies/μl of the VP60 gene per reaction. Furthermore, 74 clinical samples were detected for both RHDV1 and RHDV2. RT‐LAMP‐CRISPR/Cas12a‐based dual readout portable detection platform showed 25.68% (19/74) RHDV1‐positive samples, 43.24% (32/74) RHDV2‐positive samples, and 8.11% (6/74) RHDV1/RHDV2 double positive samples, respectively. The coincidence rates of detection RHDV1 and RHDV2 between RT‐LAMP‐CRISPR/Cas12a and quantitative real‐time‐polymerase chain reaction (qPCR) were both 97.30%. RT‐LAMP‐CRISPR/Cas12a showed higher sensitivity and detection rate compared with qPCR. Moreover, the results were visible to the naked eye within 1.5 h combined with lateral flow strips (LFSs) and visual fluorescence. The RT‐LAMP‐CRISPR/Cas12a portable platform has the advantages of high sensitivity, specificity, fast, low equipment requirements, which can be used in clinical practice in rural areas and resource‐limited settings. [ABSTRACT FROM AUTHOR]

Rabbit haemorrhagic disease (RHD) is an acute fatal disease caused by the Lagovirus rabbit haemorrhagic disease virus (RHDV), which was first reported in 1984 in China. Strains of two different genotypes (GI.1a and GI.1c) have been detected in China to date. In 2010, a new RHDV variant with a unique genetic and antigenic profile was identified in France, designated RHDV2, which rapidly spread throughout continental Europe and nearby islands. Here, we report the first outbreak of RHD induced by RHDV2 (GI.2) in rabbit farms in the Sichuan province of China. We conducted haemagglutination tests and phylogenetic analysis of the new RHDV isolate SC2020/04, which was identified as a non‐haemagglutinating strain belonging to the RHDV2 (GI.2) genogroup. Considering the serious risk of RHDV2 to the Chinese rabbit industry, the circulation of RHDV2 in the population should be carefully monitored in China. [ABSTRACT FROM AUTHOR]

• SC2020 strain is characterized by higher mortality rates and acute RHD symptoms. • Fecal route contributes more to viral dissemination. • Kits infected with SC2020 strain present more severe histological lesions than adults. • SC2020 strain is mainly distributed in the liver of rabbits. • Serum cytokine levels are significantly increased in SC2020-infected rabbits. In April 2020, rabbit hemorrhagic virus type 2 (Lagovirus europaeus GI.2), which causes highly infectious fatal rabbit hemorrhagic disease, was emerged in China. The phylogenetic analyses of the complete genome sequence of GI.2 showed that it belonged to the non-recombinant GI.3/GI.2 genotype. However, the pathogenicity of this GI.2 strain differed from that of early typical GI.2 strains in Europe. To prevent the spread of the new strain in China, its pathogenicity urgently needs to be studied. Thus, viral shedding and distribution as well as clinical symptoms, histopathological changes, and serum cytokines were studied in experimentally GI.2/SC2020-infected rabbit adults and kits. The kit group showed a shorter survival time after the challenge than the adult group did. The mortality rate was higher in the kits (80 %) than in the adults (30 %). Viral RNA could be detected in both nasal and fecal swabs, and the main dissemination route appeared to be the fecal route. Viral RNA rapidly increased in the blood of the adults and kits at 6 h post-infection, indicating that blood viral load testing can be used for early diagnosis. The most affected organs were the liver and spleen, and the lesions were more severe in the kits than in the adults. The liver contained the highest viral RNA levels. Moreover, serum interleukin (IL)-6, IL-8, IL-10, and tumor necrosis factor-alpha levels were increased in the infected rabbits. In conclusion, our findings will help to understand the evolutionary trends and pathogenic characteristics of GI.2 strains in China. [ABSTRACT FROM AUTHOR]

Rabbit hemorrhagic disease virus (RHDV) poses a significant threat to rabbits, causing substantial economic losses in rabbit farming. The virus also endangers wild populations of rabbit species and the predatory animals that rely on rabbits as a food source, thereby disturbing the ecological balance. However, the structural understanding of RHDV has been limited due to the lack of high-resolution structures. Here, we present the first high-resolution cryo-EM structures of the mature virion and virus-like particles (VLPs) derived from both full-length and N-terminal arm (NTA)-truncated VP60. These structures reveal intricate structural details of the icosahedral capsid and crucial NTA-mediated interactions essential for capsid assembly. In addition, dramatic conformational differences are unexpectedly observed between the mature virion and VLP. The protruding spikes of the A-B dimers adopt a "raised" state in the mature virion and a "resting" state in the VLP. These findings enhance our understanding of the structure, assembly, and conformational dynamics of the RHDV capsid, laying the essential groundwork for further virological research and therapeutic advancements.IMPORTANCERHDV is a pathogen with significant economic and ecological impact. By presenting the first high-resolution cryo-EM structures of RHDV, we have uncovered detailed interactions among neighboring VP60 subunits of the icosahedral capsid. The NTA of VP60 is uniquely clustered around the threefold axis of the capsid, probably play a critical role in dragging the six VP60 dimers around the threefold axis during capsid assembly. Additionally, we observed dramatic conformational differences between the mature virion and VLPs. VLPs are commonly used for vaccine development, under the assumption that their structure closely resembles that of the mature virion. Our findings significantly advance the understanding of the RHDV capsid structure, which may be used for developing potential therapeutic strategies against RHDV., Competing Interests: The authors declare no conflict of interest.