Molecular characterization of the VP1 gene of a Mexican isolate of infectious pancreatic necrosis virus

The presence of infectious pancreatic necrosis virus (IPNV) in salmonids predominantly produces a high mortality rate in first-feeding fry. Genomic analysis of the vp2 gene sequence is most commonly used to determine the genetic diversity of IPNV isolates. Recently, information obtained from the vp1 gene allowed for efficient analysis of the genetic diversity of IPNV. In this study, the vp1 gene from a Mexican IPNV isolate was characterized and compared with IPNV isolates from Europe, North America, and Asia. The results indicate that the Mexican isolate is most closely related genetically to the 2310 strain from Spain.

Characterization of infectious bursal disease virus isolates from Indonesia indicates the existence ofvery virulent strains with unique genetic changes

Sequencing of the hypervariable region of viral protein VP2 of infectious bursal disease virus (IBDV) isolates obtained from non-vaccinated chickens in Indonesia showed that the majority (16/17) were closely related to published very virulent (vv)IBDV strains. Four isolates contained identical amino acid sequences to Asian and European vvIBDVs, sharing vv-specific amino acid residues 222(Ala), 256(Ile), and 294(Ile). Eight isolates differed by one amino acid at position 222(Ala-->Ser); however, this change did not alter the pathogenicity or antigenicity of these strains. Two isolates, with amino acid substitutions at positions 272(Ile-->Thr) and 279(Asp-->Asn), did not cause clinical disease or mortality, and were therefore considered to be naturally occurring, attenuated mutants of vvIBDV. The results illustrate variability that might occur among vvIBDV strains.

Viral hemorrhagic septicemia and infectious pancreatic necrosis viruses replicate differently in rainbow trout gonad and induce different chemokine transcription profiles

Viral hemorrhagic septicemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV) are two rainbow trout (Oncorhynchus mykiss) pathogens. While IPNV is known to be vertically transmitted to the next generation through the oocyte, VHSV is known to replicate in the ovary and be transmitted horizontally through the ovarian fluid. In this work, we wanted to study whether these differences had an effect on the immune response triggered in the ovary, with a focus on the chemokine response. We have studied the kinetics of viral gene expression and the sites of replication, confirming that great differences exist between the replication of the two viruses in the gonad. Next, we studied the levels of expression of several CXC and CC chemokines in the ovary and found that while VHSV strongly triggered chemokine transcription, IPNV had almost no effect. This lack of immune response might be an advantage that permits its vertical transmission.

Detection of infectious pancreatic necrosis virus (IPNV) from asymptomatic redbanded seabream, Pagrus auriga Valenciennes, and common seabream, Pagrus pagrus (L.), using a non-destructive procedure

A non-destructive procedure based on nested RT-PCR and dot-blot hybridization has been developed for the detection of asymptomatic IPNV-carrier fish. The pair of primers designed for RT-PCR amplified a 599-bp fragment of the pVP2 region within the polyprotein gene, resulting in the detection of IPNV genotype III.1. The use of a nested RT-PCR allowed the amplification of IPNV genotypes III.1 and I.2. In addition, a 191-bp probe was designed for hybridization studies used in combination with the nested RT-PCR. The application of the nested RT-PCR to analyse blood samples from asymptomatic redbanded seabream, Pagrus auriga, and common seabream, P. pagrus, specimens showed a 53.1% and 77.8% prevalence of IPNV-carriers, respectively. The combination of nested RT-PCR and dot-blot hybridization increased the detection rates up to 100% for redbanded seabream and 94.4% for common seabream. Therefore, the protocol described in this study is highly sensitive and specific for the detection of IPNV in asymptomatic carrier fish, and, in addition, the results demonstrate the carrier state in two newly cultured sparid species in southern Spain.

Isolation and characterization of a very virulent Infectious bursal disease virus from turkey

Infectious bursal disease (IBD) is a highly contagious disease of chickens caused by Infectious bursal disease virus (IBDV). In turkeys, however, infection with classical virulent IBDV strains lead only to subclinical forms of the disease. We attempted to isolate IBDV from the bursa of turkey and characterize it. Amplification of a 743-bp fragment of VP2 gene by RT-PCR and restriction analysis of the product showed a pattern compatible with very virulent IBDV (vvIBDV). Comparison of the sequence of this isolate with those of other IBDVs and phylogenetic analysis confirmed very virulent nature of the isolate. This is the first report on the isolation of vvIBDV from turkey in Iran.

Chemokine transcription in rainbow trout (Oncorhynchus mykiss) is differently modulated in response to viral hemorrhagic septicaemia virus (VHSV) or infectious pancreatic necrosis virus (IPNV)

Chemokines not only act as chemoattractants for immune cells, but also exert immunomodulatory actions, thus modulating the immune functions of their target cells. In rainbow trout (Oncorhynchus mykiss), twenty-four chemokines have been identified to date. Even though their sequences have been reported, their biological role has been scarcely elucidated and the role that these chemokines have on the antiviral response in fish has been poorly studied. In this sense, in the current work, we have determined the levels of expression of several of these rainbow trout chemokines (CXCd, gammaIP, CK1, CK3, CK5B, CK6, CK7A, CK9 and CK12) in head kidney and spleen during the course of a viral infection using two different viruses, viral hemorrhagic septicaemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV), comparing them to the levels induced by poly I:C. We also determined the effects that the two viruses and poly I:C provoked on the levels of expression of these chemokines in vitro in head kidney leucocytes. Overall, VHSV was capable of modulating gammaIP, CXCd, CK1, CK3, CK5B, CK6 and CK12, while IPNV induced a very different chemokine profile and affected CK1, CK5B, CK6, CK7A, CK9 and CK12. On the other hand, a viral mimic such as poly I:C was capable of up-regulating gammaIP, CXCd, CK1, CK3, CK5B, CK7A and CK12. As more information becomes available concerning the immune role and target cells that these chemokines have on rainbow trout, we would be able to better interpret the importance of these differences in the pathogenicity of these two viruses.

[Molecular epidemiology of infectious bursal disease virus in Guangxi during the period of 2000 to 2007]

Tissue samples of Fabricius' bursa collected from Nanning, Yulin, Beihai and Wuzhou in the provinces of Guangxi in China during the years of 2000-2007, were detected by a established reverse transcriptase polymerase chain reaction (RT-PCR) technique for IBDV. Viral isolation was performed on the positive samples by chicken embryo inoculation via chorio-allantoic membrane (CAM). Results showed that 27 isolates of IBDV were obtained. A set of primers were designed to amplify the vVP2 of 27 isolates by RT-PCR and the PCR products were sequenced. The sequences of all the isolates and reference viruses were analyzed and compared, and their phylogenetic trees were constructed based on the nucleotide sequences. The results indicated that isolate BH11, TZ(3), 050222, YL051, NN0603, NN0611and QX0602 etc, altogether 17 isolates, which accounted for 62.96 percent of total isolates, were identified to be very virulent IBDV (vvIBDV) and have the highest homology to vvIBDV reference strains. In the phylogenetic analysis, they are divided into 3 groups and have a long distance to commonly used vaccine stains. Isolate NN040124 and YL052 were identified as intermediate-plus virulent strains and showed a highest homology to classical strains of 52-70 and STC. 8 isolates of YLZF2, 040131 etc were identified as attenuated vaccine strains and showed a highest homology to classical strain of CU1. The results from the study demonstrated that the viruses prevailing in chickens in these 4 regions in Guangxi province in the recently 7 years were vvIBDV and their origins were complex. The antigenicity of some isolates may have been drifted.

Development and validation of a short-time cell culture and multiplex reverse transcriptase polymerase chain reaction assay for infectious pancreatic necrosis virus in Mexican farm-sampled rainbow trout

The infectious pancreatic necrosis virus (IPNV) affects several species of freshwater and marine fish. In Mexico, IPNV has an important impact on farming of rainbow trout Oncorhynchus mykiss; however, IPNV distribution in Mexico is unclear. The diagnosis of IPNV is laborious; usually it is based on isolation tests in cell culture followed by immunological identification using techniques of serum neutralization, immunofluorescence, or enzyme-linked immunosorbent assay. It has recently been demonstrated that reverse transcriptase polymerase chain reaction (RT-PCR) is an adequate method for the detection of aquatic birnaviruses. However, its diagnostic use is still limited because very low titers of viable virus cannot be easily detected. In this study, a combination of short-time cell culture and multiplex RT-PCR was established for the diagnosis of IPNV in rainbow trout obtained from farms in the state of Mexico. Three primer sets were used in a single reaction in the multiplex RT-PCR to increase the probability of identifying all serotypes of IPNV serogroup A as well as to help prevent a false-negative result. This approach was able to identify samples with an IPNV concentration of just 0.01 tissue culture infective dose with 50% endpoint (TCID50)/mL, and it identified more infected fish than RT-PCR alone or first-passage cell culture alone. Moreover, this technique made the same identifications as second-passage cell culture but in approximately 30% of the time needed for second-passage cell culture. Consequently, the time and cost efficiency of IPNV diagnosis were greatly reduced.

Development of reverse-transcription loop-mediated isothermal amplification for the detection of infectious bursal disease virus

To establish a reverse-transcription loop-mediated isothermal amplification (RT-LAMP) method for rapid detection of infectious bursal disease virus (IBDV), four primers specific to six regions of the VP3 gene were designed; the VP3 region was selected because it is a conserved part of the IBDV genome. After amplification in an isothermal water bath for 70 min, samples containing IBDV generated the expected ladder-like products while other viruses generated no product. The sensitivity and specificity of the RT-LAMP assay were evaluated by comparison with reverse-transcription polymerase chain reaction (RT-PCR) and virus isolation. The assay was significantly more sensitive than normal gel-based RT-PCR. Because it is specific and simple, the RT-LAMP assay can be widely applied in clinical laboratories for rapid detection of IBVD.

Susceptibility of Atlantic cod Gadus morhua juveniles to different routes of experimental challenge with infectious pancreatic necrosis virus (IPNV)

Atlantic cod Gadus morhua L. juveniles weighing 40 g were challenged with infectious pancreatic necrosis virus (IPNV) by intraperitoneal (i.p.) or intramuscular (i.m.) injection or by bath. The amount of infectious virus was determined over 6 wk in head kidney, heart and pylorus tissues. No mortality or clinical signs were observed in either of the challenged groups. However, 6 wk after challenge virus was still present in the fish, which shows that IPNV can persist asymptomatically in cod. I.p. and i.m. injections were the most efficient routes of challenge giving the highest virus recovery. The prevalence of individuals with a viral titre > or = 500 infectious units g(-1) tissue was lower in the group of fish challenged by bath; thus bath was a less efficient route of challenge than injection. Our data also show that pylorus and head kidney are target organs for IPNV in cod, and levels of virus recovery were not considerably different between these 2 organs. Challenged by injection, the cod heart is also a target organ for IPNV. Compared to head kidney and pylorus, the heart seems to have a minor role in virus multiplication. Virus was also recovered from cohabiting fish, demonstrating that covertly infected cod may represent a reservoir of infectious IPNV for surrounding fish populations. Expression analysis of selected cod immune genes showed that i.p. injection of IPNV induced gene expression of ISG15 and LGP2, markers for the innate antiviral defence, while expression of markers for the inflammatory response (interleukins IL-1 beta, IL-8, IL-10) was not significantly increased.

Experimental study of the susceptibility of Atlantic cod, Gadus morhua (L.), to infection with an IPNV strain pathogenic for Atlantic salmon, Salmo salar L

Intraperitoneal (IP) injection, cohabitation and immersion routes of infection were used to determine if Atlantic cod, Gadus morhua (L.), of 1 and 3 g are susceptible to infectious pancreatic necrosis (IPN). Mortalities of cod injected IP were significantly higher when challenged with infectious pancreatic necrosis virus (IPNV) than with phosphate buffered saline. This is the first report of Atlantic cod mortalities caused by IPNV. Fish challenged by cohabitation had significantly higher mortalities than the controls, but mortalities of Atlantic cod challenged with IPNV by immersion were not significantly different from controls. Titres of IPNV in the tissues of infected fish were sometimes very high (range 10(2)-10(10) infectious units per gram of tissue) suggesting virus replication and titres of fish that died were generally higher than those of fish which survived. However, the relatively low mortality rates when challenged by cohabitation and immersion (20% and 17%, respectively), compared to the IP injection challenge (100%) suggest that 1 and 3 g cod have low susceptibility to IPN when challenged by more natural routes. These data strongly suggest that the cause of death of experimentally challenged cod was IPNV and further histological evidence for this came from 1 g cod challenged IP with IPNV in which the pancreas showed severe necrosis and heavy immunostaining for IPNV coincidentally with the peak of mortalities.

Reduced mucosal injury of SPF chickens by mast cell stabilization after infection with very virulent infectious bursal disease virus

Recent studies here have demonstrated that increased mast cell populations and tryptase activity contribute to lesion formation in regions of immune organs in special-pathogen-free chickens after infection with very virulent infectious bursal disease virus (vvIBDV). Mast cells and their mediators have been implicated in acute inflammatory injury after vvIBDV infection, but their precise role in this process remains elusive. In this study, the role of mast cells in the vvIBDV infection process was examined using ketotifen, a mast cell membrane stabilizer. On days 1, 2, and 3 postinfection, the bursa of Fabricius (BFs) were collected to quantify mast cells, tryptase and histamine contents by cytochemistry, immunohistochemistry and fluorospectrophotometry analyses, respectively. The results showed that the mast cell populations, tryptase expression, and histamine released increased significantly in the BFs (p<0.01) of infected birds compared to controls, and acute inflammatory responses were observed in the former. In contrast, in infected chickens pretreated with ketotifen, mast cells, tryptase, and histamine were markedly decreased (p<0.01) and probably as a result, the BFs remitted significantly. The overall results suggest that mast cells are positively involved in BF injury induced by vvIBDV infection. Inhibition of mast cell degranulation and concurrent mediator release may represent a novel strategy to modulate this process. This study, thus, advances the understanding of the acute inflammatory injury mechanisms triggered by vvIBDV infection and the contribution of mast cell activity in this process.

The interplay between infectious pancreatic necrosis virus (IPNV) and the IFN system: IFN signaling is inhibited by IPNV infection

Infectious pancreatic necrosis virus (IPNV) is a major pathogen in the aquaculture industry worldwide. Factors contributing to IPNV pathogenicity are yet poorly understood. Indications of IPNV being able to evade or counteract innate host defense come from its lack of ability to induce strong type I interferon (IFN) responses in cell culture. We show here that addition of salmon rIFN-α1 to cells prior to IPNV infection halts the viral protein synthesis and prevents processing of pVP2 into mature VP2. Furthermore, compared to pre-treatment with IFN-α1 the antiviral state in cells infected with IPNV prior to IFN-treatment, was antagonized by IPNV, as detected by higher viral titers, faster viral protein synthesis and also by reduced Mx expression. The longer headstart the virus gets, the more prominent is the weakening of IFN signaling. IPNV VP4 and VP5 inhibit IFN-induced expression from the Mx promoter, indicating that these proteins contribute to the antagonistic effect.

Continuous exposure to infectious pancreatic necrosis virus during early life stages of rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout, Oncorhynchus mykiss (Walbaum), were exposed continuously to infectious pancreatic necrosis virus (IPNV) at 0, 10(1), 10(3) or 10(5) plaque forming units (pfu) L(-1) of water to estimate the effects of chronic IPNV exposure on early life stages. Fish density averaged 35 fish L(-1) (low density) or 140 fish L(-1) (high density), and the tank flow rate was 250 mL(-1) min. Virus exposure began at 6 days before hatch and continued until fish were 44 days old. Cumulative per cent mortality, analysis of survival and hazard functions, and discrete-time event analysis were used to explore the patterns of survival and mortality. In eggs and fish exposed to IPNV, mortality significantly greater than in the 0 pfu L(-1) exposure did not occur until IPNV concentration was 10(5) pfu L(-1) at low fish density and 10(3) pfu IPNV L(-1) at high fish density. These results suggest that in the natural aquatic environment, where rainbow trout densities are likely to be considerably lower than in this study, mortality resulting from infection with IPNV will very likely not occur when ambient concentrations of virus are < or =10(3) pfu IPNV L(-1). In aquaculture rearing units, trout density is likely to be as high or higher than the densities used in this study. Therefore, continuous inputs of virus at concentrations greater than 10(1) pfu L(-1) may result in IPN epidemics in aquaculture facilities.

Estimation of infectious dose and viral shedding rates for infectious pancreatic necrosis virus in Atlantic salmon, Salmo salar L., post-smolts

Infectious dose and shedding rates are important parameters to estimate in order to understand the transmission of infectious pancreatic necrosis virus (IPNV). Bath challenge of Atlantic salmon post-smolts was selected as the route of experimental infection as this mimics a major natural route of exposure to IPNV infection. Doses ranging from 10(2) to 10(-4) 50% end-point tissue culture infectious dose (TCID(50)) mL(-1) sea water were used to estimate the minimum infectious dose for a Scottish isolate of IPNV. The minimum dose required to induce infection in Atlantic salmon post-smolts was <10(-1) TCID(50) mL(-1) by bath immersion (4 h at 10 degrees C). The peak shedding rate for IPNV following intraperitoneal challenge using post-smolts was estimated to be 6.8 x 10(3) TCID(50) h(-1) kg(-1) and occurred 11 days post-challenge. This information may be incorporated into mathematical models to increase the understanding of the dispersal of IPNV from marine salmon sites.

Detection and confirmation of a major QTL affecting resistance to infectious pancreatic necrosis (IPN) in Atlantic salmon (Salmo salar)

Infectious pancreatic necrosis (IPN) is a viral disease currently presenting a major problem to the aquaculture of Atlantic salmon (Salmon salar), during both the freshwater and seawater stages of production. Genetic variation in resistance to IPN has previously been demonstrated and the purpose of this study was to determine whether this variation includes loci of major effect. The initial QTL detection methodology utilized the limited recombination seen in male salmon to detect QTL in ten large full-sib families, using a genome-wide scan of two to three markers per linkage group. QTL were then positioned by adding additional markers to the significant linkage groups in a female-based analysis. The most significant QTL was mapped to LG 21, and further confirmation of the LG 21 QTL is provided in an analysis of the QTL flanking markers in an additional nine full-sib families from the same population. The size of QTL effect is such that the QTL flanking markers can be immediately applied in marker-assisted selection programmes to improve the resistance of salmon populations to IPN, thus reducing mortality due to the disease.

An improved in situ hybridization method for the detection of fish pathogens

A fluorescent in situ hybridization (FISH) method was developed for detection of infectious pancreatic necrosis virus (IPNV) in paraffin-embedded tissues of Atlantic salmon, Salmo salar L. Several methods of probe labelling and detection were evaluated and found unsuitable for FISH because of tissue autofluorescence. Likewise, the use of avidin to detect biotin-labelled probe was obviated by the presence of endogenous biotin. An existing approach, using digoxigenin (DIG)-labelled probes and detection by anti-DIG antibody-labelled with alkaline phosphatase, was modified to use a fluorescent substrate, 2-hydroxy-3-naphthoic acid-2'-phenylanilide phosphate/4-chloro-2-methylbenzene diazonium hemi-zinc chloride salt (HNPP/Fast Red TR). This improved method allowed sensitive detection of IPNV target, without interference from autofluorescence or endogenous alkaline phosphatase. Furthermore, the reporter produces a discrete, non-fading signal, which is particularly suitable for analysis by confocal microscopy.

Distribution of marine birnavirus in cultured olive flounder Paralichthys olivaceus in Korea

Surveys of marine birnavirus (MABV) were undertaken in cultured olive flounder Paralichthys olivaceus from the south and west coastal areas and Jeju in Korea during the period January 1999 to April 2007. MABV was detected in all seasons from the fry, juveniles and adult fish from the areas examined. Evident cytopathic effects of the virus including rounding and cell lysis were observed in chinook salmon embryo (CHSE-214) and rainbow trout gonad (RTG-2) cells, but not in fathead minnow (FHM) and epithelial papilloma of carp (EPC) cells. Nucleotide sequences of the VP2/NS junction region of the Korean isolates showed 97.8% ~ 100% similarity, and they belonged to the same genogroup. Cross neutralization tests with serotype-specific rabbit antisera against MABV strains exhibited a close antigenic relationships between strains, and were distinct from infectious pancreatic necrosis virus (IPNV) strains. Coinfection of MABV with bacteria (Streptococcus iniae, Vibrio spp.) and viruses (nervous necrosis virus, lymphocystis disease virus, viral hemorrhagic septicemia virus) was observed.

Study of the viral interference between infectious pancreatic necrosis virus (IPNV) and infectious haematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss)

The resistance of rainbow trout (Oncorhynchus mykiss) to an infectious haematopoietic necrosis virus (IHNV) challenge following a preceding non-lethal infection with infectious pancreatic necrosis virus (IPNV) was investigated through experimental dual infections. Trout initially infected with IPNV were inoculated 14 days later with IHNV. Single infections of trout with 1 of the 2 viruses or with cell culture supernatant were also carried out and constituted control groups. No mortality was noted in fish after a single infection with IPNV. This virus had no influence on the head kidney leucocyte phagocytic activity and plasma haemolytic complement activity. IHNV induced a high mortality (72%) and reduced the macrophage phagocytic activity and complement haemolytic activity. It also induced a late production of anti-IHNV antibodies which occurred after clearance of the virus in the fish. In trout co-infected with both viruses, a mortality rate of 2% occurred and the immune parameters were similar to those observed in the fish infected with IPNV only, demonstrating that in co-infected trout IPNV inhibits the effects of IHNV. The studied parameters did not allow us to define the mechanism of interference occurring between these 2 viruses, but some hypothesis are put forward to explain the interference between the 2 viruses.

Poly I:C induces Mx transcription and promotes an antiviral state against sole aquabirnavirus in the flatfish Senegalese sole (Solea senegalensis Kaup)

Mx is an interferon-induced protein that protects against viral infections. In this study the absolute number of Mx transcripts after poly I:C injection (a synthetic dsRNA) or sole aquabirnavirus (solevirus) inoculation in Senegalese sole (Solea senegalensis Kaup) has been quantified. Mx expression profiles differed clearly in both experimental conditions; the induction response was faster and more intense after poly I:C injection than after solevirus inoculation. Moreover, pre-injection of soles with poly I:C prior to solevirus infection eliminated the induction of Mx expression associated with this virus. To evaluate the possible interference of poly I:C treatments on solevirus replication, the mRNA levels of the virus capsid protein (VP2) were determined by RT-PCR. VP2 transcripts were hardly detected in poly I:C pre-injected animals from 12 to 72 h after solevirus inoculation. All these data suggest that poly I:C is able to induce an antiviral state that interferes with solevirus replication, and support the suitability of Mx expression analysis as a marker to study the defensive response against solevirus.

Isolation and quantification of infectious pancreatic necrosis virus from ovarian and seminal fluids of Atlantic salmon, Salmo salar L

Methods for the isolation and quantification of infectious pancreatic necrosis virus (IPNV) from ovarian and seminal fluids of Atlantic salmon are described. Both have utility for the non-lethal detection of IPNV in mature broodstock and for research into vertical transmission. Two experiments are described to check the efficiency of an elution method for the removal of IPNV from milt. The isolation rate for ovarian fluid of females was generally higher than that for seminal fluid of males from the same populations. In IPNV milt mixing experiments up to 99.98% of available IPNV adsorbed to Atlantic salmon spermatozoa and 20-100% of virus eluted using a variety of procedures. Titration of virus from naturally infected milt can be useful in estimating the relative vertical transmission risk from male broodstock.

Molecular characterization of field isolates and vaccine strains of infectious bursal disease virus

The present investigation was conducted to study the genetic heterogenicity and molecular polymorphism among the field isolates and vaccine strains of infectious bursal disease virus (IBDV). Samples of bursa of Fabricius from 15 suspected outbreaks of infectious bursal disease (IBD) were subjected to agar gel precipitation test (AGPT), virus isolation and reverse transcription-polymerase chain reaction (RT-PCR) combined with restriction fragment length polymorphism (RFLP). Nine out of 15 samples were found positive in AGPT while 14 were found positive both by virus isolation and RT-PCR. PCR amplified 474bp fragment from the variable region of VP2. Sac I, Stu I, Alu I, Ssp I and Mbo I restriction enzymes were used for characterization of all the 14 IBDV isolates and four reference vaccine strains. Sac I, Stu I, Alu I and Ssp I could differentiate classical virulent IBD (cvIBD) vaccine virus strains from very virulent IBD (vvIBD) field isolates by their varying restriction patterns. Based on above results two field isolates (VPL and VMK) were placed in cvIBD virus group and 12 field isolates were placed in vvIBD virus group. Virus neutralisation test (VNT) using rabbit raised Georgia strain anti-serum, however, could not differentiate between cvIBD virus and vvIBD virus. It was concluded that RT-PCR combined with RFLP assay using restriction enzymes Sac I, Stu I, Alu I and Ssp I can be used for rapid differentiation and classification of field isolates of IBDV.

Characterization of three infectious bursal disease virus isolates obtained from layer chickens in Iran

Three infectious bursal disease viruses (IBDVs) were isolated from field outbreaks in IBDV-vaccinated and non-vaccinated layer chicken flocks. Agar gel precipitation test (AGPT), immunoperoxidase staining, transmission electron microscopy (TEM), inoculation into embryonated eggs, and chicken embryo fibroblasts (CEFs) confirmed that the isolates were IBDVs. RT-PCR, restriction fragment length polymorphism (RFLP), and phylogenetic analysis demonstrated that the isolates were very virulent IBDV (vvIBDV) and showed a nucleotide sequence similarity of 96.3 to 99.8% in comparison with other vvIBDV strains. It was concluded that the Iranian isolates represented vvIBDV of serotype 1 originating from Europe, Japan, and China.

Genetic analysis of infectious pancreatic necrosis virus from Scotland

Infectious pancreatic necrosis (IPN) is a highly contagious disease of young salmonid fish, and is one of the most serious economic diseases in aquaculture. In Scotland, an increase in IPN virus (IPNV) outbreaks in seawater Atlantic salmon, Salmo salar, has been reported in recent years. The aim of this study was to analyse the VP2 gene from recent IPNV isolates from Scotland, to determine whether there are epidemiological links between IPNV isolates from farms (13), wild fish (17) and the environment (6) in order to investigate potential wild and farmed fish interactions. Comparison of the nucleotide sequence of the VP2 gene revealed that 34 of 36 isolates were 97.1-100% similar and the deduced amino acid sequences showed 97-100% identity. Two isolates from wild fish exhibited the most divergence at 85-87.3% similarity to the other isolates at the nucleotide level and 88.2-90.8% identity at the deduced amino acid level. Phylogenetic analyses revealed that 34 of 36 of the isolates from Scotland were genetically closely related to the A2 (Sp) serotype of IPNV. The two wild isolates from seatrout, Salmo trutta, and flounder, Platichthys flesus, were most closely related to the European A5 (Te) serotype. This study represents a comprehensive IPNV phylogenetic study that indicates that there are closely related or identical isolates in circulation in the marine environment, which adds evidence that disease interactions between wild and farmed fish may occur. This type of analysis is a useful tool in the management and control of fish diseases because it can assist in the identification of epidemiological links and highlight potential risks to aquaculture.