Differential Expression Profile of Chicken Embryo Fibroblast DF-1 Cells Infected with Cell-Adapted Infectious Bursal Disease Virus

RNA-Seq was used to unveil the transcriptional profile of DF-1 cells at the early stage of caIBDV infection. Total RNAs were extracted from virus-infected cells at 0, 6 and 12 hpi. RNA-Seq datasets of respective samples mapped to 56.5–57.6% of isoforms in the reference genome Galgal4.73. At 6 hpi, 23 isoforms underwent an elevated expression, while 128 isoforms were up-regulated and 5 were down-regulated at 12 hpi in the virus-infected group. Besides, 10 isoforms were exclusively expressed in the virus-infected cells. Though no significant change was detected in cytokine and interferon expression levels at the first 12 hours of infection, modulations of the upstream regulators were observed. In addition to the reported regulatory factors including EIF2AK2, MX, OAS*A, GBP7 and IFIT, IBDV infection also triggered a IFIT5-IRF1/3-RSAD5 pathway in the DF-1 cells which potentially restricted the viral replication cycle in the early infection stage. Over-expression of LIPA and CH25H, together with the suppression of STARD4, LSS and AACS genes implied a modulation of membrane fluidity and lipid raft arrangement in the infected cells. Alternative splicing of the EFR3 homolog A gene was also through to be involved in the lipid membrane regulation, and these cumulative responses projected an inhibition of viral endocytosis. Recognition of viral RNA genomes and intermediates was presumably enhanced by the elevated levels of IFIH1, DHX58 and TRIM25 genes which possess properties on detecting viral dsRNA. On the other hand, the caIBDV arrested the host's apoptotic process by inducing the expression of apoptosis inhibitors including NFKBIA/Z, TNFAIP2/3 and ITA at the first 12 hours of infection. In conclusion, the differential expression landscape demonstrated with RNA-Seq provides a comprehensive picture on the molecular interactions between host cells and virus at the early stage of infection.

Risk factors for outbreaks of infectious pancreatic necrosis (IPN) and associated mortality in Norwegian salmonid farming

Infectious pancreatic necrosis (IPN) has for many years been considered one of the most important restraints to the production of salmonids in European aquaculture. In Norway, the disease is responsible for high losses in post-smolts in the first few weeks after sea transfer. Despite the importance of IPN, there are few epidemiological studies on risk factors and mitigation strategies. In this paper, we present analyses of data from all cohorts put to sea in 2009 to 2012 on Norwegian marine salmonid farms. The data used were obtained from national registers on salmonid production and disease outbreaks. The results showed that the risk of IPN outbreak was higher for spring versus autumn cohorts, Atlantic salmon versus rainbow trout and for cohorts on farms with previous history of IPN. The risk increased with increasing cohort size and infection pressure, whereas increasing temperature and weight at sea transfer decreased the risk. Estimations from a model of cumulative mortality within the first 6 mo after sea transfer showed that mortality in cohorts with IPN increased to approximately 7.2% as compared to a 'baseline' cohort with a mortality of 3.4%. If the cohort had both IPN and pancreas disease (PD), the estimated mortality increased to 12.9%, and cohorts with both IPN, PD and heart and skeletal muscle inflammation (HSMI) had an estimated mortality of 16.6%, when all other significant factors were kept constant (these were cohort type, year, temperature at sea transfer and weight at sea transfer). Our results provide valuable inputs for mitigation strategies and for economic modelling of consequences of disease.

Molecular characterization of infectious bursal disease virus (IBDV) isolated in Argentina indicates a regional lineage

In Argentina, classical vaccines are used to control infectious bursal disease virus (IBDV); however, outbreaks of IBDV are frequently observed. This could be due to failures in the vaccination programs or to the emergence of new strains, which would be able to break through the protection given by vaccines. Hence, genetic characterization of the viruses responsible for the outbreaks that occurred in recent years is crucial for the evaluation of the control programs and the understanding of the epidemiology and evolution of IBDV. In this study, we characterized 51 field samples collected in Argentina (previously identified as IBDV positive) through the analysis of previously identified apomorphic sequences. Phylogenetic analysis of regVP2 showed that 42 samples formed a unique cluster (Argentinean lineage), seven samples were typical classical strains (one of them was a vaccine strain), and two belonged to the very virulent lineage (vvIBDV). Interestingly, when the analysis was performed on the regVP1 sequences, the field samples segregated similarly to regVP2; thus, we observed no evidence of a reassortment event in the Argentinean samples. Amino acid sequence analysis of regVP2 showed a particular pattern of residues in the Argentinean lineage, particularly the presence of T272, P289 and F296, which had not been reported before as signature sequences for any IBDV phenotype. Notably, the residue S254, characteristic of the antigenic variant, was not present in any of the Argentinean samples.

Isolation of a novel aquatic birnavirus from rainbow trout Oncorhynchus mykiss in Australia

In November 2010, a rainbow trout (Oncorhynchus mykiss) hatchery in Victoria reported increased mortality rates in diploid and triploid female fingerlings. Live and moribund fish were submitted for laboratory investigation. All fish showed hyperpigmentation of the cranial half of the body. Histological lesions were seen in all areas of skin examined despite the localised nature of the gross lesions. There was irregular hyperplasia and spongiosis, alternating with areas of thinning and architectural disturbance. Occasionally, particularly in superficial layers of epithelium, cells showed large, eosinophilic inclusions that obscured other cellular detail. A small number of fish had necrosis in dermis, subcutis and superficial muscles. Bacteriological culture of skin and gills was negative for all bacterial pathogens, including Flavibacterium columnare, the agent of columnaris disease. Attempts at virus isolation from the skin of affected fish resulted in the development of a cytopathic effect in RTG-2 cell cultures suggestive of the presence of a virus. Negative contrast electron microscopy of cell culture supernatant demonstrated the presence of viral particles with the typical morphology of birnaviruses. Preliminary molecular characterisation identified an aquabirnavirus that differed from both the Tasmanian aquabirnavirus (TABV) and other aquabirnaviruses exotic to Australia. Previous isolates of aquabirnaviruses in Australia and New Zealand have been from healthy fish in a marine environment. This is the first report of an aquabirnavirus isolated from young salmonids at a freshwater hatchery in Australia. The role of the virus in the mortality event on the farm is uncertain as no further deaths attributable to this virus have occurred in the 4 yr since its initial discovery. The virus has been provisionally named Victorian trout aquabirnavirus (VTAB).

[Development and Application of the Reverse Genetic Technologies for Infectious Bursal Disease Virus]

Infectious bursal disease virus (IBDV) is an important member of the Birnaviridae family. IBUV mainly targets the bursa of Fabricius, the central immune organ of chicken, resulting in chicken infectious bursal disease (IBD). IBD represents one of the great challenges for ongoing development of the poultry industry. Reverse genetics for IBDV emerged over twenty years ago. Since then, the technologies behind virus rescue have continually improved leading to a deep understanding of IBDV gene function and tailored vaccine development. Our lab has also been instrumental in the field of IBDV research. Here we review studies on the pathogenic mechanism and the effective prevention and control of IBD.

Functional characterization of the evolutionarily preserved mitochondrial antiviral signaling protein (MAVS) from rock bream, Oplegnathus fasciatus

Antimicrobial immune defense is evolutionarily preserved in all organisms. Mammals have developed robust, protein-based antiviral defenses, which are under constant investigation. Studies have provided evidences for the various fish immune factors sharing similarity with those of mammals. In this study, we have identified an ortholog of mitochondrial antiviral signaling protein from rock bream, Oplegnathus fasciatus. RbMAVS cDNA possesses an open reading frame (ORF) of 1758 bp coding for a protein of 586 amino acids with molecular mass of approximately 62 kDa and isoelectric point of 4.6. In silico analysis of RbMAVS protein revealed a caspase recruitment domain (CARD), a proline rich domain and a transmembrane domain. RbMAVS protein also contains a putative TRAF2 binding motif, (319)PVQDT(323). Primary sequence comparison of RbMAVS with other orthologues revealed heterogeneity towards the C-terminus after the CARD region. RbMAVS transcripts were evident in all the examined tissues. RbMAVS expression was induced in vivo after poly I:C challenge in peripheral blood cells, liver, head kidney and spleen tissues. Over-expression of RbMAVS potently inhibited marine birnavirus (MABV) infection in rock bream heart cells and induced various cytokines and signaling molecules in vitro. Thus, RbMAVS is an antiviral protein and potentially involved in the recognition and signaling of antiviral defense mechanism in rock bream.

Genetic positioning of aquabirnavirus isolates from cultured Japanese eel Anguilla japonica in Korea

Aquabirnavirus is an epizootic virus in Japanese eel Anguilla japonica farms in Korea, although its origin is unclear. In the present study, nucleotide sequences of the VP2/NS junction region of 9 Korean aquabirnaviruses from cultured eel in various areas of Korea during 2000-2009 were analyzed to evaluate their genetic relatedness to worldwide isolates. The nucleotide sequences showed more than 94.2% identity among the 9 Korean eel isolates, 71.2% identity among 16 Korean isolates from freshwater and marine fish, and 71.1% identity among 25 worldwide isolates. All 9 isolates in this study were phylogenetically classified into genogroup II, including isolates from Denmark, Spain, Taiwan and Japan, and were discrete from salmonid and marine fish isolates (genogroup I and VII) in Korea. These results suggest that the Korean eel isolates have most likely been introduced from outside the country and not from coastal areas of Korea.

Food pellets as an effective delivery method for a DNA vaccine against infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss, Walbaum)

A DNA vaccine based on the VP2 gene of infectious pancreatic necrosis virus (IPNV) was incorporated into feed to evaluate the effectiveness of this oral delivery method in rainbow trout. Lyophilized alginate-plasmid complexes were added to feed dissolved in water and the mixture was then lyophilized again. We compared rainbow trout that were fed for 3 consecutive days with vaccine pellets with fish that received the empty plasmid or a commercial pellet. VP2 gene expression could be detected in tissues of different organs in the rainbow trout that received the pcDNA-VP2 coated feed (kidney, spleen, gut and gill) throughout the 15 day time-course of the experiments. This pcDNA-VP2 vaccine clearly induced an innate and specific immune-response, significantly up-regulating IFN-1, IFN-γ, Mx-1, IL8, IL12, IgM and IgT expression. Strong protection, with relative survival rates of 78%-85.9% were recorded in the vaccinated trout, which produced detectable levels of anti-IPNV neutralizing antibodies during 90 days at least. Indeed, IPNV replication was significantly down-regulated in the vaccinated fish 45 days pi.

Molecular characterization of the VP2 gene of infectious pancreatic necrosis virus (IPNV) isolates from Mexico

Infectious pancreatic necrosis virus (IPNV) is one of the most important viruses in the Pacific salmon Oncorhynchus spp., Atlantic Salmon Salmo salar, and Rainbow Trout O. mykiss industry. This virus has been shown to produce high mortality among salmonid fry and juveniles, and survivors might become carriers. Since 2000, IPNV has affected Mexican Rainbow Trout culture, resulting in considerable economic losses. In the current study, molecular characterization of the VP2 gene of a number of Mexican IPNV isolates was done and the virus's phylogenetic relationships to IPNV reference strains were investigated. The phylogenetic analysis indicated that Mexican IPNV isolates are closely related to strains from the United States and Canada and that all Mexican IPNV isolates belong to genogroup 1. Furthermore, low genetic diversity was found between the Mexican isolates (identity, 95.8-99.8% nucleotides and 95.8-99.6% amino acids). The result of the analysis of the amino acid residues found at positions 217, 221, and 247 (alanine, threonine, and glutamic acid, respectively) could be associated with virulence, although the expression of virulence factors is more complex and may be influenced by the agent and host factors. The high percentage of identity among the VP2 genes from geographically distant IPNV isolates and the evidence of wide distribution in the country might have been facilitated by carrier trout. This hypothesis is supported by the identification of the amino acid threonine at position 221 in all Mexican isolates, a factor related to the carrier state for IPNV, as reported by other studies.

Genetic characterisation of infectious bursal disease virus isolates in Ethiopia

The objective of the investigation was to characterise infectious bursal disease viruses (IBDV) circulating in commercial and breeding poultry farms in Ethiopia between 2009 and 2011. The nucleotide and deduced amino acid sequence for VP2 hypervariable region of ten IBDVs were determined by RT-PCR, sequenced and compared to well characterised IBDV isolates worldwide. IBDV genetic material was amplified directly from bursa or cell passaged material. Phylogenetically, Ethiopian IBDVs represented two genetic lineages: very virulent (vv) IBDVs or variants of the classical attenuated vaccine strain (D78). The nucleotide identity between Ethiopian vvIBDVs ranged between 0% and 2.6%. Ethiopian vvIBDVs are clustered phylogenetically with the African IBDV genetic lineage, independent of the Asian/European lineage. This report demonstrates the circulation of vvIBDV in commercial and breeding poultry farms in Ethiopia.

Assessment of the risk of White Sturgeon to become infected and potential carriers of infectious pancreatic necrosis virus

Little scientific information is available to assess whether White Sturgeon Acipenser transmontanus can become infected and potential carriers of infectious pancreatic necrosis virus (IPNV). To assess this risk, monitoring results of adult and progeny White Sturgeon were examined from waters historically stocked with salmonid fish known to be IPNV carriers. From 1999 through 2004 White Sturgeon from a total of 30 separate families whose parentage came from waters historically stocked with IPNV carrier fish were tested. Duplicate groups of 25 juvenile Snake River White Sturgeon were waterborne exposed to 1.0×10(4) 50% tissue culture infective dose (TCID50)/mL of water for 1 h and an additional group was injected intraperitoneally with 1.0×10(5) TCID50/fish. A negative control group was handled similarly but was not exposed to the virus. No morbidity was detected in any of the treatment groups or the negative control. At 34, 40, 47, and 54 d postexposure to IPNV, virus reisolation was attempted on five fish from each group, and an additional five fish from each group were examined for histological changes consistent with an IPNV infection. At 34 and 40 d postinjection with IPNV, 20% (one of five) of the fish tested positive for the virus per sample interval; however, fish from groups that were waterborne-exposed to IPNV were all negative. At 47 and 54 d after exposure or injection with IPNV an additional five fish from each group were tested at each sample interval and all results were negative. Histological analysis of target tissue obtained from five fish per group at 34 and 54 d postinfection also failed to detect any consistent change associated with an IPNV infection. These results suggest that the risk of White Sturgeon to become infected and develop into potential carriers of IPNV is negligible.

Infectious Bursal Disease: a complex host-pathogen interaction

Infectious Bursal Disease (IBD) is caused by a small, non-enveloped virus, highly resistant in the outside environment. Infectious Bursal Disease Virus (IBDV) targets the chicken's immune system in a very comprehensive and complex manner by destroying B lymphocytes, attracting T cells and activating macrophages. As an RNA virus, IBDV has a high mutation rate and may thus give rise to viruses with a modified antigenicity or increased virulence, as emphasized during the last decades. The molecular basis of pathogenicity and the exact cause of clinical disease and death are still poorly understood, as it is not clearly related to the severity of the lesions and the extent of the bursal damage. Recent works however, pointed out the role of an exacerbated innate immune response during the early stage of the infection with upregulated production of promediators that will induce a cytokine storm. In the case of IBDV, immunosuppression is both a direct consequence of the infection of specific target immune cells and an indirect consequence of the interactions occurring in the immune network of the host. Recovery from disease or subclinical infection will be followed by immunosuppression with more serious consequences if the strain is very virulent and infection occurs early in life. Although the immunosuppression caused by IBDV is principally directed towards B-lymphocytes, an effect on cell-mediated immunity (CMI) has also been demonstrated therefore increasing the impact of IBDV on the immunocompetence of the chicken. In addition to its zootechnical impact and its role in the development of secondary infections, it may affect the immune response of the chicken to subsequent vaccinations, essential in all types of intensive farming. Recent progress in the field of avian immunology has allowed a better knowledge of the immunological mechanisms involved in the disease but also should give improved tools for the measurement of immunosuppression in the field situation. Although satisfactory protection may be provided by the induction of high neutralizing antibody titres, interference from parental antibodies with vaccination has become the most important obstacle in the establishment of control programs. In this context, recombinant HVT and immune complex vaccines show promising results.

Mutations of residues 249 and 256 in VP2 are involved in the replication and virulence of infectious Bursal disease virus

Infectious bursal disease virus (IBDV) is a pathogen of worldwide significance to the poultry industry. Although the PDE and PFG domains of the capsid protein VP2 contribute significantly to virulence and fitness, the detailed molecular basis for the pathogenicity of IBDV is still not fully understood. Because residues 253 and 284 of VP2 are not the sole determinants of virulence, we hypothesized that other residues involved in virulence and fitness might exist in the PDE and PFG domains of VP2. To test this, five amino acid changes selected by sequence comparison of the PDE and PFG domains of VP2 were introduced individually using a reverse genetics system into the virulent strain (rGx-F9VP2). Then reverse mutations of the selected residues 249 and 256 were introduced individually into the attenuated strain (rGt). Seven modified viruses were generated and evaluated in vitro (CEF cells) and in vivo (SPF chicken). For residue 249, Q249R could elevate in vitro and reduce in vivo the replication of rGx-F9VP2 while R249Q could reduce in vitro and elevate in vivo the replication of rGt; meanwhile Q249R reduced the virulence of rGx-F9VP2 while R249Q increased the virulence of rGt, which indicated that residue 249 significantly contributed to the replication and virulence of IBDV. For residue 256, I256V could elevate in vitro and reduce in vivo the replication of rGx-F9VP2 while V256I could reduce in vitro but didn't change in vivo the replication of rGt; although V256I didn't increase the virulence of rGt, I256V obviously reduced the virulence of virulent IBDV. The present results demonstrate for the first time, to different extent, residues 249 and 256 of VP2 are involved in the replication efficiency and virulence of IBDV; this is not only beneficial to further understanding of pathogenic mechanism but also to the design of newly tailored vaccines against IBDV.

Tissue distribution of infectious pancreatic necrosis virus serotype Sp in naturally infected cultured rainbow trout, Oncorhynchus mykiss (Walbaum): an immunohistochemical and nested-PCR study

This study investigates the occurrence and distribution pattern of infectious pancreatic necrosis virus (IPNV) within the pancreas, liver, kidney and spleen of naturally infected cultured rainbow trout, Oncorhynchus mykiss (Walbaum), using immunohistochemistry (IHC). A nested PCR was also employed to confirm the presence of the virus in the pooled tissues of the specimens. All the examined tissues except spleen were immunohistochemically positive for IPNV, but staining intensity and distribution pattern varied. The kidney tubules had the most intense and widespread staining by IHC, indicating a specific tissue tropism at least for this particular serotype. The nucleotide sequence had the greatest identity with the Sp serotype confirming the presence of the nucleic acid of IPNV in the pooled tissues. Based on the present findings, it could be concluded that the absence of lesions consistent with infectious pancreatic necrosis (IPN) disease in the H&E-stained sections cannot rule out the presence of the IPNV, and the use of an alternative rapid confirmatory method such as IHC with formalin-fixed, paraffin-embedded tissue sections is helpful for the final diagnosis of IPN in rainbow trout.

Spatiotemporal Phylogenetic Analysis and Molecular Characterisation of Infectious Bursal Disease Viruses Based on the VP2 Hyper-Variable Region

Background

Infectious bursal disease is a highly contagious and acute viral disease caused by the infectious bursal disease virus (IBDV); it affects all major poultry producing areas of the world. The current study was designed to rigorously measure the global phylogeographic dynamics of IBDV strains to gain insight into viral population expansion as well as the emergence, spread and pattern of the geographical structure of very virulent IBDV (vvIBDV) strains.

Methodology/Principal Findings

Sequences of the hyper-variable region of the VP2 (HVR-VP2) gene from IBDV strains isolated from diverse geographic locations were obtained from the GenBank database; Cuban sequences were obtained in the current work. All sequences were analysed by Bayesian phylogeographic analysis, implemented in the Bayesian Evolutionary Analysis Sampling Trees (BEAST), Bayesian Tip-association Significance testing (BaTS) and Spatial Phylogenetic Reconstruction of Evolutionary Dynamics (SPREAD) software packages. Selection pressure on the HVR-VP2 was also assessed. The phylogeographic association-trait analysis showed that viruses sampled from individual countries tend to cluster together, suggesting a geographic pattern for IBDV strains. Spatial analysis from this study revealed that strains carrying sequences that were linked to increased virulence of IBDV appeared in Iran in 1981 and spread to Western Europe (Belgium) in 1987, Africa (Egypt) around 1990, East Asia (China and Japan) in 1993, the Caribbean Region (Cuba) by 1995 and South America (Brazil) around 2000. Selection pressure analysis showed that several codons in the HVR-VP2 region were under purifying selection.

Conclusions/Significance

To our knowledge, this work is the first study applying the Bayesian phylogeographic reconstruction approach to analyse the emergence and spread of vvIBDV strains worldwide.

Flow cytometry detection of infectious pancreatic necrosis virus (IPNV) within subpopulations of Atlantic salmon (Salmo salar L.) leucocytes after vaccination and during the time course of experimental infection

In the present study, intracellular infectious pancreatic necrosis virus (IPNV) in salmon leucocytes was detected by flow cytometry after experimental cohabitant challenge. IPNV vaccinated, non-vaccinated and intraperitoneally (i.p.) infected salmon (virus shedders) were analysed at different times throughout the period when mortality occurred. Fish that had survived 61 days post challenge (carriers) were also analysed. In particular, we analysed the presence of IPNV in B-cells (C7G7+cells) and in neutrophils (E3D9+ cells) in head kidney leucocytes (HKL) and in peripheral blood leucocytes (PBL). IPNV was present in HKL and PBL from all challenged fish groups at all samplings, including carriers. IPNV was also found intracellular in other leucocytes than B-cells and neutrophils. During the time course of infection there were changes in proportion of B-cells and neutrophils and in proportions of IPNV+ cells. In vaccinated fish, a delay in the changes observed in the proportion of IPNV+ cells and in the proportions of the two subpopulations was identified. The vaccinated fish were protected against disease as no fish died compared to 30.8% of non-vaccinated cohabitant fish. All i.p. infected fish, except one, survived the challenge. This is consistent with previous studies and confirmed that the routes of infection can influence mortality. The analyses in this study could not identify any factors enlightening this absence of mortality in i.p. infected fish, but both flow cytometry and qRT-PCR showed that i.p. infected fish were carriers of IPNV. The present study also found that IPNV was present in both B-cells and neutrophils as well as in other leucocytes in all carriers after cohabitant challenge. These fish had survived 9 weeks post challenge and 4 weeks after mortality has ceased. The fish harbouring virus within their leucocytes might become life long carriers and represent a risk for disease outbreaks, being virus shedders. Such fish are protected from later infections if the virus exposure has resulted in protective immunity. Flow cytometry was found to be very suitable for detection of intracellular virus after in vivo challenge and the sensitivity was demonstrated by the detection of virus in carriers.

Stress-induced reversion to virulence of infectious pancreatic necrosis virus in naïve fry of Atlantic salmon (Salmo salar L.)

We have studied stress-induced reversion to virulence of infectious pancreatic necrosis virus (IPNV) in persistently infected Atlantic salmon (Salmo salar L.) fry. Naïve fry were persistently infected with a virulent strain (T₂₁₇A₂₂₁ of major structural virus protein 2, VP2) or a low virulent (T₂₁₇T₂₂₁) variant of IPNV. The fry were infected prior to immunocompetence as documented by lack of recombination activating gene-1, T-cell receptor and B-cell receptor mRNA expression at time of challenge. The fish were followed over 6 months and monitored monthly for presence of virus and viral genome mutations. No mutation was identified in the TA or TT group over the 6 months period post infection. Six months post infection TA and TT infected groups were subject to daily stress for 7 days and then sampled weekly for an additional period of 28 days post stress. Stress-responses were documented by down-regulation of mRNA expression of IFN-α1 and concomitant increase of replication levels of T₂₁₇T₂₂₁ infected fish at day 1 post stress. By 28 days post stress a T221A reversion was found in 3 of 6 fish in the T₂₁₇T₂₂₁ infected group. Sequencing of reverted isolates showed single nucleotide peaks on chromatograms for residue 221 for all three isolates and no mix of TA and TT strains. Replication fitness of reverted (TA) and non-reverted (TT) variants was studied in vitro under an antiviral state induced by recombinant IFN-α1. The T₂₁₇A₂₂₁ reverted variant replicated to levels 23-fold higher than the T₂₁₇T₂₂₁ strain in IFN-α1 treated cells. Finally, reverted TA strains were virulent when tested in an in vivo trial in susceptible salmon fry. In conclusion, these results indicate that stress plays a key role in viral replication in vivo and can facilitate conditions that will allow reversion from attenuated virus variants of IPNV.

Study of virulence in field isolates of infectious pancreatic necrosis virus obtained from the northern part of Norway

In order to study the variety of infectious pancreatic necrosis virus (IPNV) strains involved in outbreaks of infectious pancreatic necrosis (IPN) in Atlantic salmon fish farms, samples were collected from 19 different outbreaks of IPN in the northern part of Norway. The main objective of this study was to examine whether IPNV isolates of different virulence were involved in the outbreaks and could explain the variable IPN protection observed in vaccinated post-smolts in the field. Both the molecular basis of virulence of all field isolates and virulence expressed by mortality after bath challenge of unvaccinated post-smolts with eight of the isolates were studied. Very little variation among the field isolates was detected when the 578-bp variable region encoding the VP2 protein known to be involved in virulence was sequenced. The cumulative mortality after experimental challenge with field isolates genetically characterized as highly virulent was always high (40-56%), while the cumulative mortality of the same strains in vaccinated post-smolts during the field outbreaks varied from 1 to 50%. Although the tested samples came from fish vaccinated with the same vaccine product, the protection against IPN varied. These results demonstrate that differences in virulence of the isolates were not the main reason for the variation in mortality in the field outbreaks. Most of the field isolates were of high virulence, which is shown in experimental challenges to be important for mortality, but clearly other factors that might affect the susceptibility of IPN also play an important role in the outcome of an IPNV infection.

Establishing a cell line from Atlantic cod as a novel tool for in vitro studies

The present work describes the generation of a cell line from newly hatched Atlantic cod (Gadus morhua) larvae (ACL cells). Primary cultures were initiated by explant outgrowth from partially minced tissues and subcultured cells were exposed to UV radiation. After a substantial period of growth lag, cells started to proliferate and different growth conditions were tested to establish the cell line. At present, the ACL cell line has been subcultured for more than 100 passages. ACL cells had a polygonal shape and the morphology appeared homogenous with epithelial-like cells. Cell growth was dependent on the presence of foetal bovine serum and cells proliferated in a wide temperature range with optimal growth at 15 °C. By exposure to a viral dsRNA mimic (poly I:C) the cells expressed high levels of a repertoire of genes comprising both inflammatory mediators and interferon stimulated genes. Infection studies with two different viruses showed that infectious pancreatic necrosis virus (IPNV) propagated efficiently, and induced low level expression of genes of both pathways before the cells rapidly died. No productive infection was obtained with nervous necrosis virus (NNV), but a transient increase in the viral RNA level, followed by a high increase in expression of selected ISGs, suggests that the virus enters the cells but is unable to complete its replication cycle. To our knowledge, ACL cells are at the moment the only existing cell line from Atlantic cod. Our results demonstrate that ACL cells can be a useful research tool for further exploration of host-pathogen interactions and it is believed that this cell line will serve as a valuable tool also for studies within other research areas.

Genomic sequence of an infectious bursal disease virus isolate from Zambia: classical attenuated segment B reassortment in nature with existing very virulent segment A

We determined the complete nucleotide sequence of an infectious bursal disease (IBD) virus (IBDV) isolate (designated KZC-104) from a confirmed IBD outbreak in Lusaka in 2004. The genome consisted of 3,074 and 2,651 nucleotides in the coding regions of segments A and B, respectively. Alignment of both nucleotide and deduced amino acid sequences and phylogenetic analysis revealed that the genome segment A of KZC-104 was derived from a very virulent (VV) strain, whereas its segment B was derived from a classical attenuated strain. On BLAST search, the full-length segment A and B sequences showed 98 % nucleotide sequence identity to the VV strain D6948 and 99.8 % nucleotide sequence identity to the classical attenuated strain D78. This is a unique IBDV reassortant strain that has emerged in nature, involving segment B of a cell-culture-adapted attenuated vaccine.

An overview of infectious bursal disease

Infectious bursal disease (IBD) is a viral immunosuppressive disease of chickens attacking mainly an important lymphoid organ in birds [the bursa of Fabricius (BF)]. The emergence of new variant strains of the causative agent [infectious bursal disease virus (IBDV)] has made it more urgent to develop new vaccination strategies against IBD. One of these strategies is the use of recombinant vaccines (DNA and viral-vectored vaccines). Several studies have investigated the host immune response towards IBDV. This review will present a detailed background on the disease and its causative agent, accompanied by a summary of the most recent findings regarding the host immune response to IBDV infection and the use of recombinant vaccines against IBD.

[Characterization the immunogenicity of recombinant VP2 of infectious bursal disease virus containing N-terminal M2e of avian influenza virus]

OBJECTIVE

We developed subunit vaccines against H5 or H9 subtype avian influenza viruses (AIV) and infectious bursal disease viruses (IBDV). Viral protein 2 (VP2) of IBDV was used as cargo protein to display a 12-amino-acid (aa) immunodominant epitope derived from N-terminal M2 extracelluar domain (nM2e) of H5 or H9 subtype AIV.

METHODS

The aa and nucleotide sequence of nM2e was determined by comparing the available avian influenza vaccine strains and alignment the AIV sequence available in GenBank. One copy of H5 or H9 nM2e was inserted into P(BC) region of VP2 origin from IBDV B87 vaccine strain by fusion polymerase chain reaction. The VP2(BC)nM2e recombinants were cloned into Bac-to-Bac expression system and transfected to Sf9 cell. The expressed chimeric protein was characterized by indirect immunofluorescence assay and Western blotting, and subsequently was used as antigen to develop vaccine. The non-immunized chicken was given two injections with the vaccine at a 4-week interval. Serum against VP2 and nM2e was tested by indirect ELISA and virus neutralization in chick embryo fibroblast.

RESULTS

Both VP2(BC)nM2e recombinants were successfully constructed and expressed in Sf9 cell. Both chimeric proteins elicited antibody against VP2 and nM2e. The antibody level elicited by VP2(BC)nM2e(H5) vaccine was higher than that of VP2(BC)nM2e(H9).

CONCLUSION

Both chimeric proteins were immunigenic, and the efficacy of VP2(BC)nM2e(H5) was higher than VP2(BC)nM2e(H9) chicken.

Isolation and molecular characterization of a novel infectious pancreatic necrosis virus strain in returning Atlantic salmon Salmo salar from the Connecticut River, USA

After 22 years of negative viral screening results, the viral pathogen infectious pancreatic necrosis virus (IPNV) was isolated from the ovarian fluid of two pooled samples of returning Connecticut River Atlantic salmon Salmo salar during the 2007 spawning season at Richard Cronin National Salmon Station (RCNSS), Hadley, Massachusetts. Cytopathic effect was observed in Chinook salmon embryo (CHSE-214) cells, and IPNV was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR). Sequence analysis conducted by the U.S. Geological Survey's Western Fisheries Research Center determined that the isolate closely resembled the Canada_3 strain, falling into Genogroup 4 rather than Genogroup 1, which is more common in the United States. This allowed us to speculate that the Atlantic salmon were not infected during their freshwater life stage in the Connecticut River watershed but somewhere on their migratory route or feeding grounds in the Northwest Atlantic. On November 20, 2007, the Connecticut River Atlantic Salmon Commission voted to depopulate the infected stock at RCNSS and the entire suspect egg lots held at White River National Fish Hatchery, Vermont. Approximately one and a half months later, the 121 Connecticut River Atlantic salmon were euthanized and sampled for a follow-up investigation to determine the prevalence of infection. Only one kidney-spleen homogenate (male) was confirmed IPNV positive via cell culture and RT-PCR. A total of 2,983 base pairs from segment A of the RNA genome were sequenced from this fish and determined to be from a new strain (Connecticut-1) of IPNV that closely resembles Canada_2 and Canada_3 in Genogroup 4. The new strain is genetically identical to one of the first ovarian fluid isolates over a shared 130-nucleotide region, possibly indicating original transmission from a single source. The absence of IPNV from the Connecticut River's subsequent four returning Atlantic salmon year-classes may indicate that the aggressive corrective action was prudent.

Immune responses elicited in rainbow trout through the administration of infectious pancreatic necrosis virus-like particles

Virus like particles (VLPs) against viral pathogens not only constitute a novel approach for the development of antiviral vaccines for an specific virus, but also for the creation of multivalent vaccines in which antigens from other pathogens may be expressed on the surface of these VLPs. Despite positive results on protection for many of these VLPs in both fish and mammals, not many studies have focused on the immune response triggered by these particles; studies that may provide hints for the identification of immune mechanisms responsible for antiviral protection, which are mostly unknown in fish. In the current work, we have studied the levels of transcription of several immune genes in the spleen of rainbow trout (Oncorhynchus mykiss) intraperitoneally injected with VLPs from infectious pancreatic necrosis virus (IPNV) focusing on the chemokine response as well as the response of genes related to interferon (IFN) production. Surprisingly, the capacity of VLPs to induce chemokines differed from that of live IPNV, suggesting a direct effect of viral replication on the chemokine response in this organ. While VLPs up-regulated the transcription of CK3, CK10 and CXCd and down-modulated CK5B, CK6 and CK9 transcription, a previous study in which the transcription of γIP, CXCd, CK1, CK3, CK5B, CK6, CK7A, CK9 and CK12 had been studied demonstrated that IPNV only significantly up-regulated CK6 and down-modulated CK3 in the spleen. On the other hand, the administration of VLPs produced a strong mobilization to the peritoneum of CD4(+), IgM(+), IgT(+) and CD83(+) leukocytes similar to that induced by the live viral infection. In both cases, this leukocyte recruitment seemed to be greatly mediated through CK3, CK5B, CK9 and CK10 chemokine production. These results together with the fact that VLPs strongly induced non-specific lymphocyte proliferation and specific anti-IPNV antibody production point to VLPs as excellent candidates for vaccine development.

Omega-3 polyunsaturated fatty acids enrichment alters performance and immune response in infectious bursal disease challenged broilers

BACKGROUND

Infectious bursal disease (IBD) results in economic loss due to mortality, reduction in production efficiency and increasing the usage of antibiotics. This study was carried out to investigate the modulatory roles of dietary n-3 polyunsaturated fatty acids (PUFA) enrichment in immune response and performance of IBD challenged broiler chickens.

METHODS

A total of 300 day old male broiler chicks were assigned to four dietary n-3 PUFA ascending levels as the treatment groups (T1: 0.5; T2: 8.0; T3: 11.5; T4: 16.5) using combinations of tuna oil and sunflower oil. All diets were isocaloric and isonitrogenous. On day 28, all birds were challenged with IBD virus. Antibody titer, cytokine production, bursa lesion pre and post-challenge and lymphoid organ weight were recorded.

RESULTS

On d 42 the highest body weight was observed in the T2 and T3 and the lowest in T4 chickens. Feed conversion ratio of the T2 broilers was significantly better than the other groups. Although productive parameters were not responded to the dietary n-3 PUFA in a dose-dependent manner, spleen weight, IBD and Newcastle disease antibody titers and IL-2 and IFN-γ concentrations were constantly elevated by n-3 PUFA enrichment.

CONCLUSIONS

Dietary n-3 PUFA enrichment may improve the immune response and IBD resistance, but the optimum performance does not coincide with the optimum immune response. It seems that dietary n-3 PUFA modulates the broiler chicken performance and immune response in a dose-dependent manner. Thus, a moderate level of dietary n-3 PUFA enrichment may help to put together the efficiency of performance and relative immune response enhancement in broiler chickens.