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Salmonids can be co-infected by infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) under natural or experimental conditions. To reveal the influence of IPNV on IHNV in co-infections, CHSE-214 cells were inoculated with IPNV at different time intervals prior to or after IHNV infection. Propagation of IHNV was determined by an immunofluorescence antibody test, real-time quantitative polymerase chain reaction, flow cytometry, and virus titration. The results showed that when cells were inoculated with IPNV prior to IHNV, IHNV multiplication was inhibited. This inhibitory effect became stronger with increasing time intervals (P < 0.05). When cells were inoculated with IPNV after IHNV, the inhibitory effect became weaker with increasing time intervals (P < 0.05), and no significant inhibition was observed at 12 h (P > 0.05) compared with the single IHNV infection group. The findings suggest that IHNV is inhibited at the early stage of infection by IPNV and in a time dependent manner during co-infection. Furthermore, the effect of IPNV on IHNV entry and expression of IHNV entry-related genes clathrin, dynamin-2, adaptor protein 2, and vacuolar protein sorting 35 were also determined. The results showed that IPNV did not affect the amount of IHNV entering the cells. However, the expression levels of clathrin and dynamin-2 were significantly lower in co-infection than those in single IHNV infection, which suggests that IPNV likely inhibits IHNV by affecting IHNV invasion via downregulating IHNV entry-related genes clathrin and dynamin-2., Competing Interests: Declaration of competing interest All authors declare that no conflicts of interest exist., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Infectious pancreatic necrosis (IPN) is a significant disease of farmed salmonids resulting in direct economic losses due to high mortality in China. However, no gene sequence of any Chinese infectious pancreatic necrosis virus (IPNV) isolates was available. In the study, moribund rainbow trout fry samples were collected during an outbreak of IPN in Yunnan province of southwest China in 2013. An IPNV was isolated and tentatively named ChRtm213. We determined the full genome sequence of the IPNV ChRtm213 and compared it with previously identified IPNV sequences worldwide. The sequences of different structural and non-structural protein genes were compared to those of other aquatic birnaviruses sequenced to date. The results indicated that the complete genome sequence of ChRtm213 strain contains a segment A (3099 nucleotides) coding a polyprotein VP2-VP4-VP3, and a segment B (2789 nucleotides) coding a RNA-dependent RNA polymerase VP1. The phylogenetic analyses showed that ChRtm213 strain fell within genogroup 1, serotype A9 (Jasper), having similarities of 96.3% (segment A) and 97.3% (segment B) with the IPNV strain AM98 from Japan. The results suggest that the Chinese IPNV isolate has relative closer relationship with Japanese IPNV strains. The sequence of ChRtm213 was the first gene sequence of IPNV isolates in China. This study provided a robust reference for diagnosis and/or control of IPNV prevalent in China.

Infectious pancreatic necrosis is a significant disease of farmed salmonids in China. In this study, a single chain variable fragment (scFv) antibody library derived from rainbow trout (Oncorhynchus mykiss) and viral protein VP2 of a Chinese infectious pancreatic necrosis virus (IPNV) isolate ChRtm213 were co-expressed by a bacterial display technology. The library was subjected to three rounds of screening by flow cytometry (FCM) to select IPNV specific antibodies. Six antibody clones with different mean fluorescence intensities (MFI) were obtained by picking colonies at random. The antibody clones were expressed and purified. The purified IPNV-specific scFv antibodies were used successfully in Western blotting, enzyme linked immunosorbent assay (ELISA) and an immunofluorescence antibody test (IFAT). This method provides a high throughput means to screen an antibody library by flow cytometry, and isolate a panel of antibody that can be used as potential reagents for the detection and study of IPNV that are prevalent in China., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Infectious pancreatic necrosis virus (IPNV) is the causative pathogen of infectious pancreatic necrosis (IPN), which causes high mortality and great economic losses in salmon and trout aquaculture. IPNVs are divided into seven genotypes, and all IPNV isolates that have been reported in China belong to genogroups I and V. Because of restrictions on imported vaccines, China has no commercial vaccine against IPNV; Therefore, more effective antiviral drugs and vaccines are needed. Traditional Chinese medicine (TCM) has been used to treat endemic and pandemic diseases and is reported effective against viral infections. We screened a TCM library containing 1483 compounds and found that bufalin exhibited anti-IPNV activity. Bufalin inhibits infections from IPNV genogroups I and V by inhibiting viral internalization and RNA replication rather than viral attachment. In vivo results showed that bufalin significantly inhibited viral loads in IPNV-targeted tissues in rainbow trout. Mechanistic research showed that bufalin's antiviral effects occurred via Na+/K+-ATPase. Our results indicate that bufalin inhibits IPNV infections both in vitro and in vivo and may be a promising drug for treating IPNV infections. • Bufalin inhibits IPNV infection both in vitro and in vivo. • Bufalin inhibits viral internalization and RNA replication rather than viral attachment. • The antiviral effect of bufalin was via Na+/K+-ATPase. • Bufalin may be a promising drug for treating IPNV infections. [ABSTRACT FROM AUTHOR]

• A recombinant IHNV virus expressing VP2 gene of IPNV was successfully constructed. • The recombinant virus showed significant protection efficacy against IHNV and IPNV. • The recombinant virus induced upregulation of innate and adaptive immune responses. • The recombinant virus could be a vaccine candidate protecting rainbow trout against two or more diseases. Infectious pancreatic necrosis virus (IPNV) and infectious hematopoietic necrosis virus (IHNV) are two common viral pathogens that cause severe economic losses in all salmonid species in culture, but especially in rainbow trout. Although vaccines against both diseases have been commercialized in some countries, no such vaccines are available for them in China. In this study, a recombinant virus was constructed using the IHNV U genogroup Blk94 virus as a backbone vector to express the antigenic gene, VP2, from IPNV via the reverse genetics system. The resulting recombinant virus (rBlk94-VP2) showed stable biological characteristics as confirmed by virus growth kinetic analyses, pathogenicity analyses, indirect immunofluorescence assays and western blotting. Rainbow trout were immunized with rBlk94-VP2 and then challenged with the IPNV ChRtm213 strain and the IHNV Sn1203 strain on day 45 post-vaccination. A significantly higher survival rate against IHNV was obtained in the rBlk94-VP2 group on day 45 post-vaccination (86%) compared with the PBS mock immunized group (2%). Additionally, IPNV loads decreased significantly in the rBlk94-VP2 immunized group in the liver (28.6-fold to 36.5-fold), anterior kidney (21.7-fold to 44.2-fold), and spleen (14.9-fold to 22.7-fold), as compared with the PBS mock control group. The mRNA transcripts for several innate and adaptive immune-related proteins (IFN-γ, IFN-1, Mx-1, CD4, CD8, IgM, and IgT) were also significantly upregulated after rBlk94-VP2 vaccination, and neutralizing antibodies against both IHNV and IPNV were induced on day 45 post-vaccination. Collectively, our results suggest that this recombinant virus could be developed as a vaccine vector to protect rainbow trout against two or more diseases, and our approach lays the foundations for developing live vaccines for rainbow trout. [ABSTRACT FROM AUTHOR]