Heart and skeletal muscle inflammation in Atlantic salmon, Salmo salar L: a new infectious disease

Heart and skeletal muscle inflammation (HSMI) is a disease syndrome of unknown aetiology first observed in farmed Atlantic salmon, Salmo salar, in 1999. In the present study we have demonstrated for the first time that HSMI is an infectious disease. It was induced in Atlantic salmon post-smolts after injection with tissue homogenate from farmed Atlantic salmon previously diagnosed with HSMI. The lesions were also induced in cohabitating salmon given a corresponding injection without tissue homogenate. Six weeks post-challenge the fish that had been injected with tissue homogenate developed a serious epicarditis and myocarditis with mononuclear cell infiltrations in compact and spongy layers of the heart. Similar lesions were found in cohabitants after 10 weeks. The lesions were consistent with samples from field outbreaks of HSMI. No lesions were found in control fish. A viral aetiology is strongly suggested, as no difference in disease induction between an inoculum containing antibiotics and a non-treated inoculum was found. Further investigations are required in order to make conclusions regarding the cause and pathogenesis of HSMI.

Antifibrinolytic proCPU is present in the peritoneal cavity during surgery

The fibrinolytic capacity of the peritoneum plays a pivotal role in peritoneal wound healing. During surgery the balance between fibrin deposition and degradation is tilted towards deposition, leading to the formation of adhesions. In blood, carboxypeptidase U (CPU) stabilizes clots by retarding fibrinolysis. The purpose of this study was to investigate whether the more stable zymogen, proCPU, is also present in the peritoneal cavity and, if so, to examine its origin. Levels of proCPU were measured in plasma and serosal peritoneal fluid collected during surgery. Peritoneal biopsies were stained for proCPU. Two-dimensional gel electrophoresis was performed to study the protein composition of the serosal fluid compared to plasma and Western blotting to identify differences in glycosylation of proCPU, indicating possible different cellular origin. Cultured human mesothelial cells were examined for proCPU production under normal conditions and conditions mimicking surgery. We found comparable and correlating levels of proCPU in serosal fluid and plasma. ProCPU was also found where fibrin covered the injured peritoneal surface. A protein composition very similar in serosal fluid and plasma was shown by two-dimensional gel electrophoresis, and the proCPU pattern did not indicate a different origin. No proCPU production was found in cultured mesothelial cells. This is the first study to report on the presence of proCPU in the peritoneal cavity, which seems to be the result of plasma oozing out during the inflammatory reaction to the surgical trauma. This is likely to be important for the balance between fibrin deposition and degradation and thereby in the formation of postoperative adhesions.

IL-3 induces B7.2 (CD86) expression and costimulatory activity in human eosinophils

Eosinophils in tissues are often present in intimate contact with T cells in allergic and parasitic diseases. Resting eosinophils do not express MHC class II proteins or costimulatory B7 molecules and fail to induce proliferation of T cells to Ags. IL-5 and GM-CSF induce MHC class II and B7 expression on eosinophils and have been reported in some studies to induce eosinophils to present Ag to T cells. The cytokine IL-3, like IL-5 and GM-CSF, is a survival and activating factor for eosinophils and the IL-3 receptor shares with the IL-5 and GM-CSF receptors a common signal transducing beta-chain. IL-3-treated eosinophils expressed HLA-DR and B7.2, but not B7.1 on their surface and supported T cell proliferation in response to the superantigen toxic shock syndrome toxin 1, as well as the proliferation of HLA-DR-restricted tetanus toxoid (TT) and influenza hemagglutinin-specific T cell clones to antigenic peptides. This was inhibited by anti-B7.2 mAb. In contrast, IL-3-treated eosinophils were unable to present native TT Ag to either resting or TT-specific cloned T cells. In parallel experiments, eosinophils treated with IL-5 or GM-CSF were also found to present superantigen and antigenic peptides, but not native Ag, to T cells. These results suggest that eosinophils are deficient in Ag processing and that this deficiency is not overcome by cytokines that signal via the beta-chain. Nevertheless, our findings suggest that eosinophils activated by IL-3 may contribute to T cell activation in allergic and parasitic diseases by presenting superantigens and peptides to T cells.

Vaccination, prevention, and treatment of experimental autoimmune neuritis (EAN) by an oligomerized T cell epitope

Using a polypeptide oligomer harboring 16 repeats of the neuritogenic epitope (aa 58-73) of myelin P2 protein separated by spacers, enhancement of the immune response to the P2 protein, an important neuritogenic autoantigen in experimental autoimmune neuritis (EAN), was attempted. In contrast to a previous study with PLP-16-mer antigen-specific response of T cells was attenuated at all doses examined to a variable degree. Treatment of Lewis rats with the P2-16-mer up to 2 months before immunization with P2(53-78) (vaccination) or after immunization but before appearance of disease (prevention) had a strong tolerizing effect against the induction of EAN on immunization with P2(53-78). Moreover, rats injected with 200 microg of the P2-16-mer i.v. on day 11 after disease induction, at which time the initial signs of disease had appeared, were almost completely protected against progression of clinical disease, whereas animals treated with the same amount of monomeric control peptide developed severe disease (treatment). Similar results were obtained by i.v. treatment of adoptive-transfer EAN with the P2-16-mer. The lack of clinical signs of disease after 16-mer therapy could be correlated with a reduced proliferative response of P2(53-78)-specific lymph node cells. The frequency of apoptotic T cells in sciatic nerve or in lymph node cells, however, was not increased by the 16-mer treatment, suggesting that induction of anergy or other forms of peripheral tolerance may be responsible for the effect. Thus, the oligomerized P2 peptide antigen was highly effective in all three treatment modalities examined in this specific autoreactive T cell-mediated immune response.

Strain variation, based on the hemagglutinin gene, in Norwegian ISA virus isolates collected from 1987 to 2001: indications of recombination

Infectious salmon anemia (ISA) is caused by a virus that probably belongs to the Orthomyxoviridae and was first recorded in Norway in 1984. The disease has since spread along the Norwegian coast and has later been found in Canada, Scotland, the Faroe Islands, Chile, and the USA. This study presents sequence variation of the hemagglutinin gene from 37 ISA virus isolates, viz. one isolate from Scotland, one from Canada and 35 from Norway. The hemagglutinin gene contains a highly polymorphic region (HPR), which together with the rest of the gene sequence provides a good tool for studies of epizootics. The gene shows temporal and geographical sequence variation, where certain areas are dominated by distinct groups of isolates. Evidence of transmission of ISA virus isolates within and between regions is given. It is suggested that the hemagglutinin gene from different isolates may recombine. Possible recombination sites are found within the HPR and in the 5'-end flanking region close to the HPR.

Sodium polyacrylate potentiates the anti-adhesion effect of a cellulose-derived polymer

Available methods for postoperative adhesion prevention are insufficient. A previous study demonstrated that LM-200, a bioadhesive cellulose derivative was effective in reducing adhesions. Increasing the viscosity of a polymer solution enhances the tissue separating properties. Theoretically, a combination of sodium polyacrylate (PA) and LM-200 would give more viscous solutions than LM-200 alone, and thus be more efficacious. Therefore the efficacy of various combinations of LM-200 and PA was investigated. A lesion was created in the peritoneum of mice. The solutions to be tested, or saline, were given intraperitoneally. One week post-operatively, adhesion formation was quantified and expressed as a percentage of the original lesion covered with adhesions. PA (0.01 and 0.03 wt%) given separately did not differ in adhesion reducing effect from LM-200 (p = 0.3710 and 0.3481) but PA (0.1 wt%) resulted in significantly less adhesion formation (p = 0.0004). The effect of LM-200 increased significantly when adding PA (0.01 wt%) (p = 0.0007) or PA (0.03 wt%) (p < 0.0001). When adding PA (0.1 wt%) the effect was even more pronounced (p < 0.0001). The combination of a bioadhesive cellulose derivative and the polymer PA, was effective in reducing postoperative adhesion formation and a dose-dependent increase in efficacy was obtained compared to using the two components separately.

Strong cooperativeness in the mononuclear iron(II) derivative exhibiting an abrupt spin transition above 400 K

The spin crossover system, [Fe(bzimpy)(2)](ClO(4))(2).0.25H(2)O, was reinvestigated above room temperature (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine). The system exhibits an abrupt low-spin to high-spin transition at T(c) = 403 K. Liberation of a fractional amount of water does not affect the spin crossover: the system is perfectly reversible with a hysteresis width of DeltaT = 12 K. The existence of the hysteresis at such high temperature determines that the lowest limit of the solid-state cooperativity parameter is J/k > 403 K despite long iron(II) separations (10 A). The high cooperativeness has been assigned to a perfect pi-stacking of the benzimidazole rings in the crystal lattice at a distance as short as 3.6 A. Variable-temperature IR data and the heat capacity measurements match well the magnetic data. The thermodynamic properties are DeltaH = 17 kJ mol(-)(1), DeltaS = 43 J K(-)(1) mol(-)(1), so that the entropy of the spin transition shows a considerable contribution from the molecular vibrations. A theoretical model has been applied in fitting the magnetic data along the whole hysteresis path. A statistical distribution of the cooperativity parameter led to the feature that angled walls of the hysteresis loop are well reproduced.

Synthesis of linear and comb-like peptide constructs containing up to four copies of a T cell epitope and their capacity to stimulate T cells

Polypeptide constructs containing up to four copies of the T cell epitope 306-318 of influenza virus haemagglutinin have been synthesized on solid phase. Between the copies, a non-natural PEG-based spacer amino acid has been introduced. The oligomeric epitopes were analysed by RP-HPLC and ES-MS. The arrangement of the epitopes within the peptide constructs was either linear or comb-like. The proliferative response in a T helper cell assay induced by these oligomerized epitopes has been tested, showing that the linearly arranged epitopes are more effective than the comb-like oligomers.

Reduction of experimental adhesion formation by inhibition of plasminogen activator inhibitor type 1

BACKGROUND

Adhesion formation is a common cause of complications following surgery. A reduction in peritoneal fibrinolytic capacity during operation is a key mechanism in the early formation of adhesions. An increase in the main inhibitor of fibrinolysis, plasminogen activator inhibitor type 1 (PAI-1), is a major factor in the loss of fibrinolytic activity. The aim of this study was to investigate if inhibition of PAI-1 could reduce the formation of adhesions after surgery.

METHODS

Mice (n = 53) were subjected to a standard surgical procedure in order to induce adhesion formation to the abdominal side wall. At the conclusion of the operation, fragments for antigen binding of polyclonal rabbit antibody against PAI-1 (PRAP-1) were injected intraperitoneally, at two different concentrations. Control animals received an equal volume of the vehicle (saline). One week after operation adhesion formation was quantified.

RESULTS

Both doses of PRAP-1 significantly reduced adhesion formation compared with the saline control (P = 0.003 and P = 0.002). There were no signs of bleeding in the postoperative period or at reoperation.

CONCLUSION

The present observations lend further support to the hypothesis of a pivotal role of fibrinolysis in the early formation of adhesions, and open up new possibilities for adhesion reduction by inhibiting PAI-1.

Prevention of adhesions by surfactants and cellulose derivatives in mice

OBJECTIVE

To evaluate the efficacy of hydrophobically modified ethyl (hydroxyethyl) cellulose (cellulose), sodium hyaluronate (hyaluronate) and phosphatidylglycerol, in the reduction of adhesion formation.

DESIGN

Controlled study.

SETTING

Experimental academic unit, Sweden.

MATERIAL

NMRI mice. Solutions: (1) cellulose, (2) hyaluronate, (3) phosphatidylglycerol, (4) phosphatidylglycerol and cellulose, and (5) phosphatidylglycerol, cellulose and hyaluronate.

INTERVENTIONS

A standard lesion was created in the parietal peritoneum in mice. One of the viscous solutions to be tested, or saline, was given intraperitoneally.

MAIN OUTCOME MEASURES

Amount of adhesions found one week postoperatively.

RESULTS

Cellulose; phosphatidylglycerol and cellulose; and phosphatidylglycerol, cellulose and hyaluronate all significantly reduced the amount of adhesions (p=0.0002, p=0.002, p < 0.0001), as did the hyaluronate alone (p < 0.05). Phosphatidylglycerol alone did not reduce the amount of adhesions. Combining cellulose with phosphatidylglycerol, or with hyaluronate, did not improve efficacy.

CONCLUSION

Cellulose and hyaluronate were effective in reducing the formation of adhesions. Combining cellulose with hyaluronate or phosphatidylglycerol or both did not improve efficacy.

Phylogenetic analysis of infectious salmon anaemia virus isolates from Norway, Canada and Scotland

The sequences of gene segments 2 and 8 from 10 different isolates of infectious salmon anaemia virus (ISAV) sampled in Norway, Canada and Scotland between 1987 and 1999 were determined and compared. Pairwise comparisons revealed a high degree of homology between the European isolates, with identities of 98 to 100% for both genes examined. The Canadian isolate showed identities of 84 and 87 to 88% with the European isolates for the nucleotide sequence of segments 2 and 8, respectively. Phylogenetic analyses were performed to establish the interrelationship between the European virus isolates. The evolutionary rate based on 4 Norwegian isolates clustered together in the analysis of segment 2 was calculated to be 0.96 x 10(-3) nucleotides site(-1) yr(-1). On the basis of this mutation rate it was estimated that the Norwegian Glesvaer 90 and Canadian Bay of Fundy 97 isolates diverged around 1900, which coincides with transportation of salmonids between Europe and North America starting in the late nineteenth century.

Antigen-specific elimination of T cells induced by oligomerized hemagglutinin (HA) 306-318

In a previous study we reported that oligomerized T cell epitopes "superactivated" CD4+ T cells. These oligomers, consisting of 12-16 copies of a peptide epitope derived from the hemagglutinin protein of influenza virus (HA306-318), induced a specific T cell response in amounts as little as 5 pg/ml. We now show that the improved antigenicity of these multimerized epitopes can also be utilized to induce "high zone tolerance". Tolerization, similar to activation, occurred at about 3 logs lower concentration of oligomer than of peptide. HA306-318-specific T cell cultures became nonresponsive to stimulation with peptide after incubation with 0.5-5 microg/ml HA306-318 12-mer. The nonresponsiveness was accompanied by a drastic down-regulation of the TCR and by T cell elimination by apoptotic cell death. In contrast, stimulation with peptide even at 50 microg/ml led to temporary induction of anergy. Consequently, induction of tolerance with the oligomer was permanent and no recovery of the cultures was seen in recall experiments 12-14 days after high zone exposure to the 12-mer.

[Time delay in the thrombolytic treatment of myocardial infarction]

INTRODUCTION

Thrombolytic treatment is central in the treatment of patients with myocardial infarction.

MATERIAL AND METHODS

A cross-sectional study was conducted to determine the time delay incurred in thrombolytic treatment of patients with myocardial infarction in Ostfold Hospital, Fredrikstad, Norway. Over a seven-month period, 317 patients were diagnosed as having myocardial infarction. 80 patients (25%) received thrombolytic therapy, 68 of whom (85%) were eligible for the study. 12 patients were excluded either because of not meeting the inclusion criteria or because of incomplete data.

RESULTS

The following median times were recorded: from onset of chest pain till first contact with the health care services, 59 minutes; from first contact till arrival at hospital, 32 minutes; from hospital arrival till initiation of treatment, 40 minutes; from onset of chest pain till initiation of treatment, 147 minutes. 38% of the patients received thrombolysis within 120 minutes of pain onset, and 35% received treatment within 30 minutes of arrival in hospital. There was no difference in time delay before contacting health care services among patients with or without a previous history of coronary heart disease, except for those who took nitroglycerine at onset of symptoms. They had the longest time delay.

INTERPRETATION

In order to reduce time delay, doctors should give better instructions to patients with a previous history of coronary heart disease and conduct regular training programmes for hospital interns and nurses. It is further assumed that prehospital ECG and direct admission to the coronary care unit, or initiation of thrombolysis in the emergency department or in the ambulance, would result in a considerable reduction in time delay.

Initial events in infectious salmon anemia virus infection: evidence for the requirement of a low-pH step

We have investigated the initial steps in the interaction between infectious salmon anemia virus (ISAV) and cultured cells from Atlantic salmon (SHK-1 cell line). Using radioactively or fluorescently labelled viral particles we have studied the binding and fusion kinetics and the effect of pH on binding, uptake, and fusion of ISAV to SHK-1 cells and liposomes. As pH in the medium was reduced from 7.5 to 4.5, the association of virus to the cells was nearly doubled. The same effect of pH was observed when fusion between ISAV and liposomes was analyzed. In addition, the binding of ISAV to intact SHK-1 cells and to cell membrane proteins blotted onto filters was neuraminidase sensitive. However, the increased binding induced by low pH was not neuraminidase sensitive, probably reflecting activation of a fusion peptide at low pH. By using confocal fluorescence microscopy, the increased fusion of fluorescently labelled ISAV with the plasma membrane due to low pH could be demonstrated. When vacuolar pH in the cells was raised during inoculation with chloroquine or ammonium chloride, both electron and confocal microscopy showed accumulation of ISAV in endosomes and lysosomes. Production of infectious virus could be increased by lowering the extracellular pH during infection. Furthermore, chloroquine present during virus inoculation also caused a reduction in the synthesis of viral proteins in ISAV-infected cells as well as in the production of infective virus. These results indicate that ISAV binds to sialic acid residues on the cell surface and that the fusion between virus and cell membrane takes place in the acid environment of endosomes. This provides further evidence for a high degree of similarity between ISAV and influenza virus and extends the basis for the classification of this virus as a member of the Orthomyxoviridae family.

Conformational variants of class II MHC/peptide complexes induced by N- and C-terminal extensions of minimal peptide epitopes

Class II MHC molecules are known to exist in conformational variants. "Floppy" and "compact" forms of murine MHC molecules, for example, are discriminated by their migration behavior on SDS/PAGE and represent empty and ligand-loaded forms. Here we show that formation of distinctly faster-migrating ligand complexes (F-forms) rather than the normal compact (C-) forms of HLA-DR1 or -DR4 results from extensions of minimal peptide epitopes (such as HA306-318 or IC106-120) by approximately 10 amino acids at either the N or the C terminus. Two similar but distinct F-forms (FI and FII) were detected, depending on the site of the extension. Both F-forms were characterized by increased surface hydrophobicity and reduced SDS-stability. Native gel separations and size exclusion chromatography indicated that the F-forms had increased hydrodynamic radii compared with the C-form and an apparent size similar to that of empty MHC molecules. The regions on the ligand overhangs responsible for the effect began at a distance of approximately 5 amino acids on either side of the epitopes, comprised 4-8 amino acids (i.e., a total overhang of 9-14), and did not have a particular sequence preference. The possible functional significance of these forms is discussed.

Time course tissue distribution of infectious salmon anaemia virus in experimentally infected Atlantic salmon Salmo salar

Atlantic salmon Salmo salar L. were injected intraperitoneally with infectious salmon anaemia virus (ISAV)-infective tissue homogenate to clarify the tissue distribution of ISAV in a time course study. Fish were sampled at 11 different intervals between 1 and 40 d post-infection (p.i.) and mid-kidney, head kidney, liver, spleen, intestine, gills, muscle and heart were tested for the presence of ISAV by reverse transcriptase polymerase chain reaction (RT-PCR). The results showed that during a disease outbreak, ISAV is present in most organs. It was possible to detect ISAV at all sampling times in at least 1 of the fish examined. However, for the first 8 d p.i. positive RT-PCR results were predominantly found in samples from the head kidney and mid-kidney. Fish giving positive samples after Day 13 p.i. were RT-PCR positive in most organs. These results indicated that between Days 8 to 13 p.i. considerable replication of the virus occurred, combined with wide tissue dissemination.

First identification of infectious salmon anaemia virus in North America with haemorrhagic kidney syndrome

Haemorrhagic kidney syndrome (HKS), a serious disease affecting Atlantic salmon on the east coast of Canada, was determined to be caused by infectious salmon anaemia virus (ISAV) through the isolation of the pathogen on the SHK-1 (salmon head kidney) cell line and confirmation by ISAV-specific immunofluorescent antibody test (IFAT) and reverse transcriptase polymerase chain reaction (RT-PCR). In addition, the defining histopathology of HKS could be reproduced following the injection of material that rendered challenged fish ISAV-positive by cell culture in the absence of any other detectable pathogen. Preliminary nucleotide sequence comparison does not suggest any direct epidemiological connection between the Canadian and Norwegian isolates.

Characterization and applications of a monoclonal antibody against infectious salmon anaemia virus

The preparation of the first monoclonal antibody (MAb) against the orthomyxovirus-like infectious salmon anaemia (ISA) virus is described. Characterization of the MAb included isotyping, enzyme-linked immunosorbent assay (ELISA), immunofluorescent staining of virus infected cell cultures (SHK-1 cells), immunoelectron microscopy (IEM) of negatively stained virus preparations, virus neutralization assay and haemagglutination inhibition assay. The MAb reacted with ISA virus preparations both with immunofluorescent staining and in ELISA. No reactions were observed in cell cultures infected with other viruses infecting salmonids including infectious pancreatic necrosis (IPN) virus, viral haemorrhagic septicaemia (VHS) virus and infectious haematopoietic necrosis (IHN) virus. The MAb was also shown to neutralize ISA virus infection in cell cultures and to inhibit the haemagglutination reaction. IEM demonstrated binding to the surface of negatively stained ISA virions. Thus, it is concluded that the MAb binds to the haemagglutinin on the virion surface. Furthermore, using immunofluorescent staining of virus infected cell cultures, reactivity against all the 13 ISA virus strains currently available was demonstrated. Using the MAb, a simple, rapid direct immunofluorescent assay for ISA virus detection and titration in 96-well tissue culture plates was developed. Infectivity titrations by this method correlated well with titration by cytopathic effects. The reliability of the assay was demonstrated by close agreement in virus infectivity titres among different assays for the same virus that were performed on the same day and on different days. A method for detection of viral antigen in cryosections from ISA diseased fish is also reported that may prove useful for the diagnosis and control of ISA.

Polymers that reduce intraperitoneal adhesion formation

BACKGROUND

Viscous macromolecules and phospholipids have been shown to reduce postoperative adhesion formation. The ideal agent, or combination of agents, still remains to be identified.

METHODS

The effect of hydrophobically modified ethyl (hydroxyethyl) cellulose (HM-EHEC) and polyquarternium-24 (LM-200), two cellulose-derived polymers, and of sphingomyelin, was examined in an animal model. Adhesions were induced in the parietal peritoneum in a standardized manner and quantity, and the morphology of adhesion formation was evaluated after 7 days.

RESULTS

A significant reduction in adhesion formation was seen in animals receiving LM-200 (P=0.013) and HM-EHEC (P=0.012) as a short-term treatment compared with controls given saline, but not in animals receiving sphingomyelin (P=0.733). Additional effects were seen in the animals receiving LM-200 as a prolonged treatment (P< 0.001) compared with controls. There was no difference in the magnitude of the inflammatory response between the groups.

CONCLUSION

These results suggest that hydrophobically modified polymers are efficient in reducing adhesions, without affecting the inflammatory response.

Training in community psychiatry: new opportunities

The authors describe the impact on training that accompanied an assignment of senior (PGY-4) residents to work one-half day each week for a six month period at a community-based agency concerned with the care of persons with severe and persistent mental illness who were formerly homeless. As the goals and methods of psychiatric training are rethought and adapt to programmatic shifts and economic pressures, new opportunities open up to move treatment and training to the "front lines" in the community where an innovative therapeutic armamentarium for persons with severe and chronic mental illness is developing.

Superactivation of an immune response triggered by oligomerized T cell epitopes

The peptides bound to class II major histocompatibility complex (MHC) molecules extend out both ends of the peptide binding groove. This structural feature provided the opportunity to design multivalent polypeptide chains that cross-link class II MHC molecules through multiple, repetitive MHC binding sites. By using recombinant techniques, polypeptide oligomers were constructed that consist of up to 32 copies of an HLA-DR1-restricted T cell epitope. The epitope HA306-318, derived from influenza virus hemagglutinin, was connected by 12- to 36-aa long spacer sequences. These oligomers were found to cross-link soluble HLA-DR1 molecules efficiently and, upon binding to the MHC molecules of a monocyte line, to trigger signal transduction indicated by the enhanced expression of some cell surface molecules. A particularly strong effect was evident in the T cell response. A hemagglutinin-specific T cell clone recognized these antigens at concentrations up to three to four orders of magnitude lower than that of the peptide or the hemagglutinin protein. Both signal transduction in the monocyte and the proliferative response of the T cell were affected greatly by the length of the oligomer (i.e., the number of repetitive units) and the distance of the epitopes within the oligomer (spacing). Thus, the formation of defined clusters of T cell receptor/MHC/peptide antigen complexes appears to be crucial for triggering the immune response and can be used to enhance the antigenicity of a peptide antigen by oligomerizing the epitope.

Characterization of infectious salmon anemia virus, an orthomyxo-like virus isolated from Atlantic salmon (Salmo salar L.)

Infectious salmon anemia (ISA) virus is the cause of infectious salmon anemia in farmed Atlantic salmon. The virus has been shown to contain RNA with structural characteristics similar to those of accepted members of the Orthomyxoviridae. Further biochemical, physiochemical, and morphological characterization of ISA virus was undertaken to clarify its taxonomic position. The virus was found to be sensitive to chloroform, heat, and low pH and agglutinated erythrocytes from fish. Erythrocytes from mammals or birds were not agglutinated. Receptor-destroying enzyme activity was detected, and the nature of this enzyme was suggested to be an acetylesterase. The buoyant density of the virus was 1.18 g/ml in sucrose and CsCl gradients. The maximum rate of virus replication was observed at 15 degrees C, while no virus was produced at 25 degrees C. Actinomycin D inhibited viral replication, and viral antigen was detected in nuclei by immunofluorescence. The addition of trypsin to the culture medium during virus replication had a beneficial effect on virus replication. ISA virus contains four major polypeptides with estimated molecular sizes of 71, 53, 43, and 24 kDa. Electron microscopy revealed structures closely resembling the nucleocapsids of influenza virus. Mushroom-shaped surface projections were a distinctive morphological feature, which differed from the rod-shaped hemagglutinin projections of the influenza viruses. The data reported here support the relationship of ISA virus to the Orthomyxoviridae, although ISA virus differs from influenza viruses in some morphological characteristics and in showing restricted hemagglutination, in different specificity of the receptor-destroying enzyme, in different polypeptide profile, in being unable to replicate at temperatures above 25 degrees C, and in host range.