Susceptibility of mud crabs (Scylla paramamosain) to the infection with decapod iridescent virus 1

Abstract

Mud crabs are among the most important aquaculture species globally. Recently, the decapod iridescent virus 1 (DIV1) has garnered significant attention for causing mass mortality events in crustaceans. The epidemiological investigation revealed a high prevalence of DIV1 in cultured mud crabs. Therefore, understanding the susceptibility of mud crabs to DIV1 is crucial for raising awareness among farmers and mitigating economic losses from potential outbreaks. Experimental infections with DIV1 showed 100 % mortality in intramuscularly injected (IM group) crabs and 60 % in those given oral administration (PO group). Nested PCR confirmed that mud crabs from both groups were positive for DIV1 and significantly elevated DIV1 loads in these mud crabs. Histopathological analyses revealed the presence of eosinophilic and basophilic inclusions in the hepatopancreas, muscle, gill, and stomach tissues of DIV1-infected mud crabs, while transmission electron microscopy (TEM) revealed numerous viral particles in the host cell cytoplasm. Notably, in addition to exhibiting symptoms like slow response and loss of appetite, some infected crabs exhibited distinctive body reddening, possibly a unique symptom of DIV1 infection in mud crab. The lethal dose 50 (LD₅₀) test demonstrate that DIV1 is highly virulent to mud crabs. It was also observed that DIV1 replicated extensively in various tissues of mud crabs resulting in severe tissue damage. These findings demonstrate that mud crabs are susceptible hosts of DIV1, and DIV1 is highly pathogenic to them. Furthermore, the study highlights the risk of cross-species transmission in polyculture systems, as healthy Litopenaeus vannamei can contract DIV1 from infected mud crabs. These results emphasize the necessity for enhanced monitoring and control measures for DIV1 in mud crab farming to prevent viral outbreaks effectively.