Global shrimp farming is increasingly threatened by various emerging viruses. In the present study, a novel picornavirus, Penaeus vannamei picornavirus (PvPV), was discovered in moribund White leg shrimp (Penaeus vannamei) collected from farm ponds in China in 2015. Similar to most picornaviruses, PvPV is non-enveloped RNA virus, with a particle diameter of approximately 30 nm. The sequence of the positive single-stranded RNA genome with a length of 10,550 nts was characterized by using genome sequencing and reverse transcription PCR. The existence of PvPV related proteins was further proved by confirmation of viral amino acid sequences, using mass spectrometry analysis. Phylogenetic analysis based on the full-length genomic sequence revealed that PvPV was more closely related to the Wenzhou shrimp virus 8 than to any other dicistroviruses in the order Picornavirales. Genomic sequence conservative domain prediction analysis showed that the PvPV genome encoded a large tegument protein UL36, which was unique among the known dicistroviruses and different from other dicistroviruses. According to these molecular features, we proposed that PvPV is a new species in the family Dicistroviridae. This study reported the first whole-genome sequence of a novel and distinct picornavirus in crustaceans, PvPV, and suggests that further studies of PvPV would be helpful in understanding its evolution and potential pathogenicity, as well as in developing diagnostic techniques.

A new emerging disease called “translucent post-larvae disease” (TPD) or “glass post-larvae disease” (GPD) of Penaeus vannamei, characterized by pale or colorless hepatopancreas and digestive tract, has become an urgent threat to the shrimp farming industry. Following this clue that treatment of an antibacterial agent could alleviate the disease, systematic investigation of the potential infectious agent of TPD was conducted using bacterial identification and artificial challenge tests to fulfill Koch’s postulates. A dominant bacterial isolate, Vp-JS20200428004-2, from the moribund individuals was isolated and identified as Vibrio parahaemolyticus based on multi-locus sequence analysis. However, Vp-JS20200428004-2 differed from the V. parahaemolyticus that caused typical acute hepatopancreatic necrosis disease. Immersion challenge tests revealed that Vp-JS20200428004-2 could cause 100% mortality within 40 h at a dose of 1.83 × 106 CFU/mL, and experimental infected shrimp showed similar clinical signs of TPD. The Vp-JS20200428004-2 could be re-isolated and identified from the experimental infected individuals. Moreover, histopathological analysis of diseased samples indicated that Vp-JS20200428004-2 caused severe necrosis and sloughing of epithelial cells of the hepatopancreas and midgut in shrimp individuals both naturally and experimentally infected. Our present results indicated that Vp-JS20200428004-2 is a highly virulent infectious agent associated with the TPD and deserves further attention.

Covert mortality nodavirus (CMNV), from the Nodaviridae family, is characterized by its unique cross-species transmission and wide epidemic distribution features. In this study, Macrobrachium rosenbergii was proved to be infected naturally by CMNV, which further expand the known host range of CMNV. Here, 61.9% (70/113) of the M. rosenbergii samples collected from Jiangsu Province were CMNV positive in the TaqMan RT-qPCR assay, which indicated the high prevalence of CMNV in M. rosenbergii. Meanwhile, the sequences of CMNV RdRp gene cloned from M. rosenbergii were highly identical to that of the original CMNV isolate from Penaeus vannamei. In situ hybridization (ISH) and histology analysis indicated that the intestine, gill, hepatopancreas and ovary were the targeted organs of CMNV infection in M. rosenbergii, and obvious histopathological damage including vacuolation and karyopyknosis were occurred in the above organs. Notably, the presence of CMNV in gonad alerted its potential risk of vertical transmission in M. rosenbergii. Additionally, numerous CMNV-like particles could be observed in tissues of hepatopancreas and gill under transmission electron microscopy. Collectively, our results call for concern of the potential negative impact of the spread and prevalence of CMNV in M. rosenbergii on its aquaculture, as well as providing a renewed orientation for further investigation and exploration of the diverse pathogenic factors causing M. rosenbergii diseases.