Outbreak of Mud Crab Reovirus ( MCRV ) in a Mud Crab ( Scylla serrata ) Fattening Facility in the Ashtamudi Backwaters, West Coast of India

The present study documents a confirmed outbreak of Mud Crab Reovirus (MCRV) in Scylla serrata from an open-water fattening facility in the Ashtamudi backwaters, Kerala, representing the first report of MCRV from the west coast of India. Mud crab farming has gained economic importance across Indian coastal states, but viral infections such as MCRV-related sleeping disease (SD) pose a critical threat to industry sustainability due to associated high mortalities. Moribund crabs exhibited gross pathological signs including gill atrophy, lethargy, reduced feeding and carapace biofouling. Histopathological analysis revealed widespread tissue degeneration, viral inclusions in gills, muscle and hepatopancreas. Transmission Electron Microscopy (TEM) confirmed the presence of non-enveloped, icosahedral viral particles within hepatopancreatic tissues, consistent with reovirus morphology. Reverse Transcription- Polymerase Chain Reaction (RT-PCR) further validated MCRV infection across multiple tissues. This study highlights the urgent need for regional biosecurity frameworks, seed certification and targeted surveillance to prevent viral dissemination in open estuarine aquaculture systems.