High prevalence of CsRV2 in cultured Callinectes danae: Potential impacts on soft-shell crab production in Brazil.

Crabs can be infected by a variety of pathogenic micro-organisms but the most damaging are viruses. Naturally-occurring Callinectes sapidus reovirus 1 (CsRV1) is thought to contribute to mortality of Callinectes sapidus in soft crab culture in the USA. In Brazil, soft crabs are frequently produced using Callinectes danae, which suffers a similar rate of mortality in culture as C. sapidus. This study investigated whether CsRV1 could be detected in healthy or dead Callinectes danae from Paraná, Brazil and kept in captivity, we also evaluated the relationship between viral infection, and biochemical and behavioral parameters. C. danae from Paranaguá Bay were kept in a recirculation system for 14 days and subjected to weekly biochemical analyses and a reflex action mortality predictors (RAMP) test. RT-qPCR assays for CsRV1 were negative for all samples. However, electrophoretic analysis of extracted RNA from some crabs showed a pattern of 12 dsRNA bands that indicated intense infection by a reovirus with a genome organization different from CsRV1. The banding pattern was indistinguishable from a putative novel reovirus detected in C. sapidus in Rio Grande do Sul, Brazil, provisionally called CsRV2. The prevalence of dsRNA of CsRV2 showed no significant difference between crabs that died and survived. Interestingly, the presence of CsRV2 dsRNA was correlated with a significant reduction in glycogen concentration in hepatopancreas and a decrease in reflex action. The results obtained in this study are an early glimpse of the occurrence of reoviruses in C. danae and their potential effects in soft-shell crab systems in Brazil.