Confirmation of susceptibility of swimming crab to infection with Decapod iridescent virus 1

As a newly found virus that seriously threatens the economic crustacean aquaculture, the susceptible host range of Decapod iridescent virus 1 (DIV1) plays a critical role in both epidemic prevention and international trade. The swimming crab, Portunus trituberculatus, is widely distributed in the coastal waters of Asia and has become an important economic species in China. In the present study, healthy swimming crabs Po. trituberculatus were artificially infected with DIV1 (isolate SHIV 20141215) through intramuscular injection and per os pathways. The infected individuals showed symptoms with decreased vitality, retarded reaction, anorexia, and mortalities of 100% and 50%, respectively. Nested PCR showed that all the moribund individuals and some surviving individuals were DIV1-positive. Histological examination revealed that eosinophilic inclusions and karyopyknosis existed in hemocytes of gills, hepatopancreas, ovaries, and muscles of diseased Po. trituberculatus, which was also verified by the positive signal of in situ DIG-labeling loop-mediated isothermal amplification (ISDL) at the same location of these tissues. Transmission electron microscopy (TEM) of ultrathin sections showed that typical DIV1 virions, the virogenic stmma, and the process of nucleocapsid formation existed in hemocytes. Quantitative detection results showed that gills and epidermis of the diseased Po. trituberculatus had the highest DIV1 load, while the gonads and hepatopancreas had the lowest DIV1 load. The above-mentioned results support that Po. trituberculatus is a newly confirmed susceptible host for infection with DIV1. Furthermore, the epidemiological survey showed that the DIV1 detection rates of farmed Po. trituberculatus, wild Helice tientsinensis, and wild Hemigrapsus penicillatus were relatively high, from 6.9% (2/29) to 42% (22/53). The findings warn that poly-culture with shrimps and crabs has a nonnegligible risk of cross-species transmission of pathogens, and wild crabs are very likely to be vectors of DIV1 to an aquaculture system.