Mortality from scale drop disease in farmed Lates calcarifer in Southeast Asia     

Saengchan Senapin  Ha Thanh Dong  Watcharachai Meemetta  Warachin Gangnonngiw  Pakakul Sangsuriya  Rapeepun Vanichviriyakit  Molruedee Sonthi  Bunlung Nuangsaeng 《Journal of fish diseases》2019,42(1):119-127

In Southeast Asia, a new disease called scale drop disease (SDD) caused by a novel Megalocytivirus (SDDV) has emerged in farmed Asian sea bass (Lates calcarifer) in Singapore, Malaysia and Indonesia. We received samples from an Eastern Thai province that also showed gross signs of SDD (loss of scales). Clinical samples of 0.2–1.1 kg L. calcarifer collected between 2016 and 2018 were examined for evidence of SDDV infection. Histopathology was similar to that in the first report of SDDV from Singapore including necrosis, inflammation and nuclear pyknosis and karyorrhexis in the multiple organs. Intracytoplasmic inclusion bodies were also observed in the muscle tissue. In a density‐gradient fraction from muscle extracts, TEM revealed enveloped, hexagonal megalocytiviral‐like particles (~100–180 nm). By PCR using primers derived from the Singaporean SDDV genome sequence, four different genes were amplified and sequenced from the Thai isolate revealing 98.7%–99.9% identity between the two isolates. Since viral inclusions were rarely observed, clinical signs and histopathology could not be used to easily distinguish between SDD caused by bacteria or SDDV. We therefore recommend that PCR screening be used to monitor broodstock, fry and grow‐out fish to estimate the current impact of SDDV in Southeast Asia and to prevent its spread.  相似文献   

CRISPR-based platform for rapid,sensitive and field-deployable detection of scale drop disease virus in Asian sea bass (Lates calcarifer)     

Thanwarat Sukonta  Saengchan Senapin  Watcharachai Meemetta  Thawatchai Chaijarasphong 《Journal of fish diseases》2022,45(1):107-120

Scale drop disease virus (SDDV) is a major pathogen of Asian sea bass that has emerged in many countries across the Asia Pacific since 1992 and carries the potential to cause drastic economic losses to the aquaculture sector. The lack of an approved vaccine for SDDV necessitates timely prevention as the first line of defence against the disease, but current diagnostic platforms still face challenges that render them incompatible with field applications, particularly in resource-limited settings. Here, we developed a novel detection platform for SDDV based on a CRISPR-Cas12a-based nucleic acid detection technology combined with recombinase polymerase amplification (RPA-Cas12a). Using the viral adenosine triphosphatase (SDDV-ATPase) gene as a target, we achieved the detection limit of 40 copies per reaction and high specificity for SDDV. The coupling with fluorescence and lateral flow readouts enables naked-eye visualization and straightforward data interpretation requiring minimal scientific background. Compared with semi-nested PCR in field sample evaluation, our RPA-Cas12a assay is more sensitive and capable of detecting SDDV in asymptomatic fish. Importantly, the entire workflow can be carried out at a constant temperature of 37°C within an hour from start to finish, thus removing the need for an expensive thermal cycling apparatus and long turnaround times associated with PCR-based methods. Therefore, owing to its high accuracy, rapidity and user-friendliness, the developed RPA-Cas12a platform shows the potential for diagnosis of SDDV at point of need and could be a valuable tool to help protect fish farming communities from large-scale epidemics.  相似文献