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1.
Preliminary experiments are described which aimed to identify compounds that could inhibit the attachment of Flavobacterium branchiophilum strains LAB4a and ATCC 35035 to the gills of rainbow trout. Total inhibition was never achieved, regardless of the compound tested. Formalin-killed or acetone-killed F. branchiophilum cells retained at least some of their adherent nature, relative to untreated (live) cells. Adherence was reduced by 22–33% following immersion of fish in one litre of water containing 0.21 mg of a homologous crude fimbrial extract. When fish were immersed in water containing hyperimmune rainbow trout antiLAB4a serum, a dose-dependent decrease in attachment (a reduction of 15% to 63%) of LAB4a to the gills was observed. Rainbow trout anti-LAB4a serum also reduced the attachment of ATCC 35035 to the gills, but this reduction was not significant. Adherence of LAB4a was not inhibited following exposure of fish to group 1 carbohydrates (arabinose, mannose and xylose), group 2 carbohydrates (dextrose, galactose and lactose), group 3 carbohydrates (galactosamine, glucosamine and fucose) or group 4 carbohydrates (N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, N-acetyl-neuraminic acid and the globoceramide glycolipid from human erythrocytes). In contrast, when rainbow trout erythrocytes were incubated with the bacteria prior to bath challenge, this resulted in an 87% and 53% reduction in gill-associated LAB4a and ATCC 35035 antigen, respectively, following immersion of rainbow trout in this suspension.  相似文献   

2.
Efficacy of mineral oil-based experimental injection vaccines against Flavobacterium psychrophilum were tested in rainbow trout, Oncorhynchus mykiss (Walbaum), under laboratory and field conditions. The vaccines consisted of formalin- or heat-inactivated whole bacterium cell preparations of two different serotypes (Fd and Th) or a combination of serologically different F. psychrophilum (Fd and/or Th and/or Fp(T);Th). Specific antibody responses against the bacterium in plasma and skin mucus were evaluated post-vaccination with enzyme-linked immunosorbent assay. Efficacy of the vaccinations was determined by challenge trials to F. psychrophilum with the vaccinated rainbow trout. Significantly higher antibody levels in plasma were detected in vaccinated fish compared with mock-vaccinated fish. Injection vaccination did not trigger specific antibody production in the skin mucus. Significantly higher survival of i.p. vaccinated fish compared with non-vaccinated fish was observed during the challenge. The results suggest that mineral oil-based injectable vaccines containing formalin- or heat-inactivated virulent cells of F. psychrophilum effectively triggered specific antibody production and protected the fish against bacterial cold water disease.  相似文献   

3.
The variation of virulence of Renibacterium salmoninarum , the causative agent of bacterial kidney disease (BKD) in salmonid fish, was studied by infecting rainbow trout, Oncorhynchus mykiss (Walbaum), with two isolates (strains 325 and 932) from diseased Atlantic salmon, Salmo salar L., and one isolate (strain 4366) from an apparently healthy Atlantic salmon. Coho salmon, Oncorhynchus kisutch (Walbaum), were injected with the strain 932 to estimate difference in fish species resistance. Fish were removed by random sampling for other study purposes, a study design possible with analysis of lifetime distributions incorporating both sampling-, death- and survival-times. At the end of the experiment, the rainbow trout infected with strains 325, 932 and 4366 had a survival probability of 33%, 51% and 72%, respectively. The coho salmon infected with strain 932 had a 26% survival probability. The strain differences were significant according to the log-rank test, and the risk ratio between the strains ranged from 1·8 to 5·4. The strain from the apparently healthy fish was least virulent. The survival of the fish species was different over time. Rainbow trout were more likely to die early in the time course, but high numbers of coho died later, resulting in an overall risk of mortality of 1·4 in favour of rainbow trout. Differences in virulence may reflect changed selective pressure on R. salmoninarum when introduced from feral stocks into the environment of fish farms.  相似文献   

4.
Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease (CWD) and rainbow trout fry syndrome (RTFS), causes high mortality in cultured salmonids. The present study was designed to determine the role antibody plays in conferring protection to rainbow trout fry, Oncorhynchus mykiss (Walbaum), by passive immunization with convalescent serum or serum from adult rainbow trout immunized with F. psychrophilum, and goat anti-F. psychrophilum serum. In each experiment, rainbow trout fry were injected intraperitoneally with antiserum and challenged by subcutaneous injection with a virulent strain (CSF-259-93) of F. psychrophilum 24-h post-immunization. Relative percentage survival (RPS) ranged from 9-42% when rainbow trout fry (mean weight 1.3 g) were injected with a 1:2 dilution of 25 microL of convalescent serum ranging in enzyme-linked immunosorbent assay antibody titres from 1600-102400. Rainbow trout fry (mean weight 1.0 g) passively immunized with 25 microL of serum from immunized adult fish exhibited RPS values of up to 57%. In each of these experiments, RPS increased with increasing antibody titres against F. psychrophilum. Passive immunization with 25 or 50 microL goat anti-F. psychrophilum serum, however, did not confer protection to fry (mean weight 1.3 g). These results suggest that trout antibody plays a role in conferring protection to F. psychrophilum, but antibody alone is unable to provide complete protection.  相似文献   

5.
During a 2-year period, bacterial fish pathogens were monitored on five rainbow trout, Oncorhynchus mykiss (Walbaum), freshwater farms in Denmark. A total of 1206 fish were examined and 361 bacterial isolates were identified phenotypically. Enteric redmouth disease, furunculosis and rainbow trout fry syndrome/coldwater disease were recorded. Infections caused by Flavobacterium psychrophilum occurred most frequently, but only one outbreak of enteric redmouth disease caused by Yersinia ruckeri serotype O1 and one of furunculosis caused by Aeromonas salmonicida were recorded during the monitoring period. Flavobacterium psychrophilum was isolated on all farms, both during disease outbreaks and from fish without any signs of disease. Serological investigations of F. psychrophilum showed that serotype Th was the dominant serotype found. The serotypes Th and Fd were involved in disease outbreaks of fry and larger fish. All isolates of F. psychrophilum showed proteolytic activities; however, a few isolates, belonging to serotype FpT did not degrade elastin and were not associated with mortality. Increasing resistance problems to oxytetracycline were demonstrated. More than half of the F. psychrophilum isolates showed resistance to oxolinic acid and oxytetracycline. No antibiotic resistant isolates were found among Y. ruckeri and A. salmonicida .  相似文献   

6.
The virulence of eight Flavobacterium columnare strains was studied to find correlations between several virulence-related factors and virulence. Virulence was tested in vivo using rainbow trout, Oncorhynchus mykiss (Walbaum). Suggested virulence-related factors such as production of the degradative enzyme chondroitin lyase, plasmid occurrence and adhesion capability were studied in vitro. Infection with the four most virulent strains resulted in 95-100% mortality within 114 h. Chondroitin lyase activity was found to be significantly related to the virulence of the strains at 25 degrees C and it was also shown to be temperature-dependent, being higher at 25 degrees C than at 20 degrees C. Virulence was not plasmid associated. The adhesion capability of the strains in vitro varied substantially when tested on crude mucus-coated slides and no statistical relationship between adhesion and virulence was found using this method.  相似文献   

7.
Abstract. On the basis of previous observations, in vivo experiments were conducted in rainbow trout, Oncorhynchus mykiss (Walbaum), to detect possible competition between strains of Aeromonas salmonicida differing in their pattern of resistance to antimicrobial drugs. Serial infections, or reinfection of naturally-infected trout, were induced by intramuscular injection. Surviving fish were artificially stressed, and all dying fish were examined using selective media to assess the type of latent infection. Secondary infections with virulent strains always resulted in mortality and reisolation of the secondary strain in pure culture. However, when trout having undergone the two successive infections were stressed, the primary strain was always reisolated. Primary strains seem to be able to survive in unknown locations within cells or tissues, regardless of their virulence or growth potency. Although a protective effect conferred by latent infection to secondary challenge could not be clearly proven, such mechanisms resemble what occurs in premunition and could be of epidemiological interest.  相似文献   

8.
In this study, 318 bacterial strains were isolated from the gastrointestinal (GI) tracts of 29 rainbow trout, Oncorhynchus mykiss (Walbaum). These bacteria were screened in vitro for their ability to inhibit growth of Flavobacterium psychrophilum, the causative agent of coldwater disease. Bacteria observed to inhibit F. psychrophilum growth were further screened against rainbow trout bile, as an indicator of their ability to survive in the GI tract. This screening resulted in narrowing the pool to 24 bacterial isolates. Those 24 isolates were then tested for pathogenicity in rainbow trout by intraperitoneal injection. Following a 28‐day challenge, eight isolates were shown to cause direct mortality and were eliminated from further study. As a result, 16 bacterial isolates were identified as probiotic candidates with the potential to control or reduce disease caused by F. psychrophilum.  相似文献   

9.
Rainbow trout, Oncorhynchus mykiss (Walbaum), fry fed with a diet containing high levels of oxidized lipid, i.e. 46/128–54/164 meq kg−1 oil, fared less well than controls following challenge with Flavobacterium psychrophilum , the causative agent of rainbow trout fry syndrome (RTFS) . In three experiments, a greater number of fish fed with the diet containing oxidized lipid died after challenge in comparison to the controls. Moreover, the pathogen was recovered as pure culture growth from the gills and kidney of dead fry. The use of diets rich in oxidized lipids led to dystrophic changes in the liver, kidney and muscle. In comparison, histopathological changes were not observed in fish fed control diets. Overall, a link was demonstrated between the presence of elevated levels of oxidized lipids in the diet and the development of RTFS.  相似文献   

10.
Abstract. The epidemiology of epizootic haematopoietic necrosis virus (EHNV) infection was studied in farmed rainbow trout, Oncorhynchus mykiss (Walbaum). Estimates of mortality during five outbreaks on a commercial farm from 1986 to 1992 ranged from 0033 to 0.2% per day and total mortality did not exceed 3–4% in any outbreak. Affected fish were 0+ and less than 125 mm forklength. Clinical signs were non-specific, and laboratory examination was required to confirm the diagnosis. At the height of the outbreak in 1992, EHNV was demonstrated by virus isolation and antigen capture ELISA in 89% of clinically affected fish and 51% of dead fish, while the prevalence of infection in apparently healthy in-contact fish was 4%. Two and 4 months later the virus was not detected in a group of apparently healthy fish that had been affected earlier. Antibodies specific for EHNV were not found in rainbow trout from the infected farm; however, strong humoral responses were detected by ELISA in two immunized fish, indicating that the virus was immunogenic. These data suggested that EHNV was poorly infective but highly virulent in rainbow trout. Clinical EHNV infection was positively correlated with high rearing density and a low rate of water exchange, and therefore, with presumed poor water quality. Water temperature, which ranged from 11 to 17°C during outbreaks, did not appear to determine the incidence of clinical infection. EHNV infection in farmed rainbow trout was preceded by infection in free-living redfin perch, Perca fluviatilis L., in the water catchment, but it was uncertain whether this represented the source of infection for rainbow trout.  相似文献   

11.
Abstract. Laboratory-raised Cryptobia -susceptible brook charr, Salvelinus fontinalis (Mitchill), and rainbow trout, Oncorhynchus mykiss (Walbaum), were vaccinated intraperitoneally with a live Cryptobia salmositica vaccine (250000 parasites per fish), and 4 weeks later were challenged with the pathogen (250000 parasites per fish). Unvaccinated and infected brook charr had high parasitaemias but no clinical signs of disease, while unvaccinated and infected rainbow trout had anaemia and general oedema. Vaccinated and challenged fish had very low parasitaemias compared to unvaccinated and infected brook charr and rainbow trout. Complement fixing antibodies were detected in vaccinated and challenged fish 2 weeks after challenge. Unvaccinated and infected brook charr had consistently higher litres of complement fixing antibody than unvaccinated and infected rainbow trout. Parasitaemias were lower in all fish in which titres of complement fixing antibody were high. In a second experiment, brook charr inoculated intraperitoneally or intramuscularly with 100000 C. salmositica per fish had high parasitaemias but no anaemia or other clinical signs. The results show that susceptible brook charr do not suffer from cryptobiosis and may serve as reservoir hosts for C. salmositica in areas where the disease is prevalent. Vaccination to reduce the parasitaemia when fish become infected may be a control strategy in these areas.  相似文献   

12.
Abstract. Salmonid fish at fish farms in northern and central Finland and perch, Perca fluviatilis L., roach, Rutilus rutilus (L.), and whitefish, Coregonus sp., from four lakes in central Finland were studied between 1985 and 1990 for the occurrence of Yersinia ruckeri. The bacteria were found in fish from both areas, but in most cases, only single diseased salmon, Salmo salar L., brown trout, S. trutta L., rainbow trout, Oncorhynchus mykiss (Walbaum), whitefish and perch were encountered and were always connected with stress conditions. One clinical outbreak occured in salmon fingerlings in northern Finland, and the fish were successfully treated with trimethoprim-sulpha. Monthly monitoring of lake fish revealed two symptomless carrier perch in two lakes. Outwith the main study a moribund perch with yersiniosis was found in a polluted lake, and for the first time in Finland, a rainbow trout was also found to have contracted yersiniosis in a small private pond. Sorbitol-positive and negative isolates have been found to occur in both moribund and carrier farmed fish, indicating that the sorbitol test is not essential when evaluating the pathogenicity of Y. ruckeri.  相似文献   

13.
The influence of rearing conditions on Flavobacterium columnare infection of rainbow trout, Oncorhynchus mykiss (Walbaum), was studied experimentally in the laboratory and at a fish farm. In experiment I, the effect of parasitic infection on columnaris disease was studied using F. columnare carrier fish. The fish were exposed to Diplostomum spathaceum cercariae and a set of other stressors in order to induce clinical columnaris infection. Parasitic infection and other stressors failed to induce the disease. Disease occurred when the fish were challenged with F. columnare, but D. spathaceum infection did not enhance the severity of the infection. In experiment II, the influence of rearing density and water temperature was studied. Overall mortality was highest in fish at normal rearing density with high temperature (+23 degrees C). At low temperature (+18 degrees C) mortality was not affected by rearing density, but the transmission of columnaris disease was faster at normal rearing density at both temperatures. This supports the view that reduction of fish density could be used in prevention of columnaris disease especially if water temperature is high. Because the lower rearing density can also decrease the transmission of ectoparasites and penetrating endoparasites, it could be an efficient tool in ecological disease management.  相似文献   

14.
A challenge model for comparison of the virulence of epizootic haematopoietic necrosis virus (EHNV) to European stocks of redfin perch, Perca fluviatilis L., and rainbow trout, Oncorhynchus mykiss (Walbaum), was tested. The model investigated intraperitoneal (IP), bath and cohabitation routes at 10, 15 and 20 °C for 5–6 g fish and 15 °C for 20 g perch. In the IP challenges of perch, significant mortality occurred at 15 °C and 20 °C. In challenge trials for rainbow trout, significant mortalities were observed in IP and bath challenges at 20 °C. The mortality observed in IP challenged 20 g perch was not significantly different from that recorded for 6 g fish challenged IP. No significant mortality was observed in any other treatment groups. Re-isolation of ranavirus was confirmed by IFAT and was consistently associated with dead or moribund fish in the trial groups challenged with EHNV. The findings indicate that EHNV does not pose a high risk for wild perch and trout populations in Europe by natural exposure. Mortality appears to be primarily a function of environmental factors, with temperature playing an important role, and not just the presence of the virus in the fish.  相似文献   

15.
Rainbow trout, Oncorhynchus mykiss (Walbaum), sea trout, Salmo trutta L., and Atlantic salmon, Salmo salar L., were experimentally infected with Flavobacterium psychrophilum in order to evaluate any species differences in susceptibility to the bacterium. Furthermore, differences in pathological changes and distribution of the bacteria in internal organs were studied. The bacteria were injected intraperitoneally in two doses, high dose (Hd) 1 x 10(7) colony forming units (CFU) fish(-1) and low dose (Ld) 1 x 10(6) CFU fish(-1). The mortalities in the Ld groups varied between 0 and 7.5% and in the Hd groups between 55-70%. No significant differences in mortality between the species were recorded. Clinical signs and pathological findings were similar in the three species and in accordance with those of rainbow trout fry syndrome. Rainbow trout showed more pronounced lesions in the spleen compared with the other species. Necrosis of renal tubular epithelium and haematopoietic tissue was most prominent in rainbow trout and Atlantic salmon. Intracellular eosinophilic droplets in the kidney tubular epithelium were a prominent finding in rainbow trout and sea trout surviving the infection. The distribution of the bacteria in internal organs was similar in the three species, as studied with immunohistochemistry.  相似文献   

16.
Abstract. The attachment of Vibrio pathogens to cells of rainbow trout, Oncorhynchus mykiss (Walbaum), was studied by use of species-specific monoclonal antibodies and indirect FITC- immunofluorescence microscopy. Vibrio anguillarum, V. ordalii and V. parahaemolyticus attached to cultured cells of rainbow trout gonads, various tissues of cryostat sections of whole fish, and smears of gills, intestine, buccal mucosa and skin. The attachment was inhibited by prior incubation of bacteria with monoclonal antibodies at titres of 1:32, or less. Other Vibrio pathogens used in this study did not attach to any trout cells. The research provides approaches to study the mechanisms of bacterial attachment in the onset of Vibrio infections.  相似文献   

17.
Adult rainbow trout, Oncorhynchus mykiss (Walbaum), maintained in either fresh or sea water were vaccinated with a live Cryptobia salmositica vaccine. All vaccinated fish were protected 4 weeks later against the cryptobiosis, while unvaccinated rainbow trout developed the disease (e.g. high parasitaemia and severe anaemia) after challenge with virulent C. salmositica . There was also no disease in vaccinated fish when they were transferred from fresh to sea water immediately after vaccination. Complement fixing antibodies (CFAbs) were detected in vaccinated fish and the CFAbs lysed parasites under in vitro conditions. The antibody titres increased rapidly at one week post-challenge in vaccinated fish in fresh water and vaccinated fish transferred from fresh water to sea water after vaccination. However, the production of CFAbs was delayed by one week in vaccinated fish in sea water and the antibody titre was significantly lower than that in fish maintained in fresh water.  相似文献   

18.
The effect of hydrogen peroxide (H2O2) treatment on the clearance of formalin-killed Flavobacterium branchiophilum from the gills of rainbow trout was examined. In untreated control fish, clearance was characterized by a rapid initial phase, with 50% reduction in bacterial antigen in the first 12 h after exposure. The bacteria then cleared more gradually, with total clearance being achieved by 40 h. Treatment of fish with 100 p.p.m. H2O2 did not influence bacterial clearance compared to untreated controls. Exposure for 1 h to H2O2 concentrations ≤ 100 p.p.m. caused no detectable clinical signs or evidence of ultrastructural damage to the respiratory epithelium. However, levels in excess of this caused significant gill damage.  相似文献   

19.
Flavobacterium psychrophilum is the aetiological agent of bacterial coldwater disease (CWD), and this pathogen has large economic impacts on salmonid aquaculture worldwide. Previously, it was demonstrated that high levels of protection against F. psychrophilum challenge were conferred to rainbow trout, Oncorhynchus mykiss (Walbaum), by immunization with distinct molecular mass fractions of the bacterium, and specific antibodies were correlated with protection. In this study, an immunoproteomic analysis of F. psychrophilum was performed using two-dimensional polyacrylamide gel electrophoresis and Western blotting with serum from fish immunized with high- and mid-molecular mass fractions of the bacterium. Mass spectrometry was used to determine the protein identity, and 15 immunogenic proteins were positively identified following Mascot searches of the F. psychrophilum genome. Based on known function and immunogenicity of homologous proteins in other bacterial pathogens, antibodies specific for several of the identified proteins may be important for protective immunity from CWD. These include outer membrane protein OmpA (P60), trigger factor, ClpB, elongation factor G, gliding motility protein GldN and a conserved hypothetical protein. This work increases the understanding of the protective humoral immune response of rainbow trout against these distinct molecular mass fractions of F. psychrophilum and provides new potential targets for recombinant protein vaccine development.  相似文献   

20.
To further characterize the putative role of constitutive and inducible plasma proteins in innate resistance to furunculosis, the present authors compared the alterations in profiles of plasma proteins in resistant and susceptible salmonids, i.e. rainbow trout, Oncorhynchus mykiss (Walbaum), and brook trout, Salvelinus fontinalis (Mitchill), respectively. Rainbow trout were injected with prednisolone acetate and exposed to higher water temperature (18 °C versus 10 °C), or injected with purified lipopolysaccharide (LPS) from a virulent strain of Aeromonas salmonicida , and plasma components were examined by two-dimensional polyacrylamide electrophoresis . Two days after A. salmonicida LPS exposure, rainbow trout had a four- to five-fold increase in concentrations of plasma proteins composed of p48, p19 and p16 subunits, and a significant decrease in a 100-kDa protein group. Consistent elevation or depletion of proteins corresponding to previously reported rainbow trout A. salmonicida LPS-binding pentraxins and lectins in plasma were not observed. Brook trout exposed to A. salmonicida LPS did not have any consistent plasma protein changes. There were no significant alterations in major plasma proteins following temperature shock and prednisolone acetate administration in rainbow trout plasma. These studies demonstrate that rainbow trout with LPS-induced sterile inflammation have few alterations in major plasma proteins or LPS-binding proteins, and do not exhibit the spectrum of acute phase changes induced by inflammation in mammals.  相似文献   

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