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1.
To determine the dynamics of the transmission of Aeromonas salmonicida ssp. salmonicida infection, chinook salmon, Oncorhynchus tshawytscha, were exposed to bacteria by cohabitation. The latent period (time between exposure and infectivity) was determined by exposing a group of chinook salmonid fingerlings to A. salmonicida by bath, then, at daily intervals, by holding five exposed (donor) fish with approximately 50 naive fish for 24 h. The latent period was 3 days post-infection and the time period between the initial exposure to bacteria and the beginning of bacterial shedding was 4.5 days for the same animals. The prevalence and intensity of infection in the donor fish, to which recipient fish were exposed, i.e. the level of exposure, was highly correlated with the development of disease in recipient (susceptible) chinook salmon (r2 = 0.57). An experiment was conducted to determine the daily progress of infection and development of a furunculosis epidemic among recipient fish by cohabiting a single exposed fish with 43 unexposed salmon. At daily intervals, all fish (in seven treatment tanks and one control tank daily) were sacrificed and tested for the presence of A. salmonicida in the kidney (n = 3520). Over 10 days, mean prevalence among recipient fish reached 75% and disease related mortality exceeded 50%. Bacterial concentrations in the water continued to increase over the duration of the experiment in concert with the number of infected animals present in the population.  相似文献   

2.
Abstract. The infectivity of the bacterial fish pathogen Aeromonas salmonicida subsp. salmonicida to Atlantic salmon, Salmo salar L., in sea water was investigated and found to be similar to that reported for fresh water. The minimal infective dose in short duration bath exposures (1–3 days) was 104 colony-forming units (cfu) per ml, while prolonged exposure for three weeks, but not for 1 week, produced infection with 102 cfu/ml. Intragastric intubation of A. salmonicida established infection with doses of >105 cfu. Release of bacteria from dead or morbid infected fish was monitored and found to be in the order of 105–108 cfu/fish/h. These results emphasize the importance of removing dead fish from farm sites.  相似文献   

3.
Abstract The abundances of Aeromonas salmonicida subsp. salmonicida in the water and in the surface microlayer was studied during the initial phase of a cohabitant infection experiment with Atlantic salmon, Salmo salar L., smolt. Aeromonas salmonicida was detected in the water samples only until the intraperitoneally infected smolt were dead and had been removed. In the lipid rich surface microlayer, A. salmonicida was detected in high concentrations from the day of the first fish mortality and throughout the rest of the experiment. The significance of the high cell surface hydrophobicity is discussed as a possible reason for enrichment of A. salmonicida at the air-water interface.  相似文献   

4.
Abstract The development and applicability of a dose-controlled experimental infection with atypical Aeromonas salmonicida in carp is described. The proliferation and clinical manifestations of experimentally induced carp erythrodermatitis mimicked a natural infection. An in-vivo assay was used to evaluate the lethal properties of cell-free culture supernatants and a simple serum-free growth medium was devised for maintaining the virulence of the challenge strain. Depending on the inoculation dose, a sublethal (chronic) to a lethal (acute) infection could be induced, and a dose-response relation was observed between A. salmonicida inoculum size and carp mortality. The dose-controlled experimental infection was used as a challenge test for laboratory evaluation of the efficacy of potential vaccine candidates. The vaccine candidates tested, a cell envelope preparation, purified lipopolysaccharide and purified A-layer (ACE) protein showed no protection or only a feeble one at the best, while formalinized whole cells showed a consistent but only moderate protection. In contrast, when concentrated, detoxified culture supernatant was used, the carp were protected against a subsequent lethal challenge. These observations indicate that immunity against A. salmonicida extracellular products is of prime importance.  相似文献   

5.
Arctic charr ( Salvelinus alpinus L.) were fed diets based on a commercial recipe supplemented with either linseed, soybean or marine oil prior to cohabitant challenge with Aeromonas salmonicida ssp. s almonicida . Mortality varied significantly between the three dietary groups. Highest mortality (48%) was observed in fish fed the marine oil and the lowest mortality (20%) was in the group fed soybean oil. Transmission electron microscopy (TEM) examination of the digestive tract of uninfected fish demonstrated substantial numbers of bacterial cells between microvilli. However, only a few bacteria were recovered that were associated with the microvilli of infected fish. Immunocytochemical staining/labelling investigations using TEM and an immunogold method were performed on mid-gut segments of fish fed the marine oil diet and showed augmentation of goblet cells and the presence of A. salmonicida ssp. salmonicida in the gastrointestinal tract of diseased fish after challenge with the pathogen. It is suggested that the gastrointestinal tract could be an infection route of A. salmonicida ssp. salmonicida. The greater prevalence of goblet cells supports the suggestion that sloughing off mucus is a protective response against bacterial infections. These results make an important contribution to our understanding of how nutrition can affect the disease resistance of fish.  相似文献   

6.
Turbot was shown to be sensitive to injection challenges by Aeromonas salmonicida subsp. achromogenes (Asa). A systemic disease was induced and the bacterium was isolated from various internal organs. Histopathological changes involved haemorrhages, necrosis and degeneration in skin and muscle, haemorrhages and necrosis in kidney, degeneration in the heart muscle, and fusion of the secondary gill lamellae. A polyvalent commercial salmon vaccine, containing A. salmonicida subsp. salmonicida as one of five antigens, did not confer protection in turbot against an experimental Asa infection 13 weeks post-vaccination. Vaccination induced a significant antibody response against Asa cells but not against extracellular products of the bacterium. The results of the study indicate that Asa may be a potential threat to turbot farming and that the development of new turbot vaccines is needed.  相似文献   

7.
The pathogenic bacterium Aeromonas salmonicida is the causative agent of the destructive disease furunculosis in salmonids. Horizontal transmission in salmonids has been suggested to occur via the skin, gills and/or intestine. Previous reports are contradictory regarding the role of the intestine as a route of infection. The present study therefore investigates the possibility of bacterial translocation across intestinal epithelia using Ussing chamber technology, in vitro. Intestinal segments were exposed for 90 min to fluorescein isothiocyanate-labelled pathogenic A. salmonicida. Sampling from the serosal side of the Ussing chambers showed that bacteria were able to translocate across the intestinal epithelium in both the proximal and distal regions. Plating and subsequent colony counting showed that the bacteria were viable after translocation. During the 90 min exposure to A. salmonicida, the intestinal segments maintained high viability as measured by electrical parameters. The distal region responded to bacterial exposure by increasing the electrical resistance, indicating an increased mucus secretion. This study thus demonstrates translocation of live A. salmonicida through the intestinal epithelium of rainbow trout, suggesting that the intestine is a possible route of infection in salmonids.  相似文献   

8.
In this study experimental challenges with Moritella viscosa, the causative agent of winter ulcers in salmonids, were performed on juvenile Atlantic cod and Atlantic halibut. The challenges involved both intramuscular (i.m.) and intraperitoneal (i.p.) injections and bath with a strain originally isolated from Atlantic salmon. Cod was found to be significantly more sensitive than halibut to the infection. Both fish species were found to be more sensitive to i.m. than i.p. challenges. Both challenges induced a systemic disease in cod and halibut, but only cod was infected with an experimental bath challenge. Pathognomonic signs were found to be comparable with those described in M. viscosa-infected salmon and turbot. The main distinguishing pathological sign was that the cod showed host response to M. viscosa infection resulting in granuloma formation in infected tissues, which is a known response of cod to a infection with another Gram-negative bacterium, Aeromonas salmonicida. Re-isolation of M. viscosa from kidneys of cod and halibut with clear disease signs was problematic and optimization of isolation measures is needed. The results of this study indicate that M. viscosa infection may be a risk factor in cod farming, but that halibut is more resistant.  相似文献   

9.
Abstract. Fish surviving infection with the pathogenic ciliated protozoan, Ichthyophthirius multifiliis (Fouquet, 1876), become resistant to subsequent infection by the parasite. The acquired immunity suggests that development of a vaccine against the parasite may be possible. Because of the advantages of immunoprophylaxis for treatment of the disease, an effort has been made to determine whether fish exposed to killed parasite preparations can resist subsequent lethal challenge. Both the route of administration and the effects of stage specific antigens have been examined. Channel catfish vaccinated by intraperitoneal (i.p.) injection or bath immersion with killed I multifiliis tomites show 100% mortality following a standard challenge protocol. Similarly, 100% mortality was observed in test groups injected with tomite cilia. In both cases, a consistent difference in days to death between control and test group animals was observed. Although complete mortality was seen with fish injected with tomite preparations, fish vaccinated with killed trophonts (the feeding stage of the parasite) had a much greater degree of protection with approximately 50% of fish surviving an otherwise lethal challenge. Finally, animals injected intraperitoneally with live tomites showed nearly complete immunity and were identical in their response to fish which survive natural infection. The response of fish vaccinated with live parasites indicates that animals injected intraperitoneally can develop surface immunity and that i.p. injection is a suitable route of administration for potential I. multifiliis vaccines.  相似文献   

10.
Plasma samples obtained from rainbow trout either experimentally infected with Aeromonas salmonicida or injected with either A. salmonicida lipopolysaccharide (LPS) or a commercial A. salmonicida vaccine (Lipogen) were analysed by enzyme immunoassay to evaluate changes in rainbow trout ladderlectin (RTLL) concentrations during the acute phase response (APR). Plasma RTLL concentrations in fish injected with A. salmonicida LPS, vaccine or live A. salmonicida varied over a 10 day period, but did not significantly increase. In contrast, fish experimentally infected with A. salmonicida exhibited a modest, but statistically significant ( P  <   0.05), decrease in RTLL concentration. These studies demonstrate that RTLL is not detectably induced during the trout APR to sterile inflammation or A. salmonicida infection, but plasma concentration of this protein may be reduced during bacterial infection.  相似文献   

11.
Abstract. Aeromonas salmonicida , the aetiologic agent of furunculosis, causes high mortality in cultured salmonids. Experiments were conducted to determine the therapeutic and prophylactic efficacy of passive immunization against furunculosis in brook trout, Salvelinus fontinalis (Mitchill), infected by immersion. Rabbit hyperimmune serum was produced against a virulent strain of A. salmonicida and an aliquot of this serum was absorbed with cells of a non-virulent strain of A. salmonicida. Immunoglobulins from aliquots of the absorbed and non-absorbed serum were purified using affinity chromatography. Each serum or immunoglobulin preparation was tested in passive immunization experiments. Brook trout were infected by immersion in a suspension of virulent A. salmonicida , and passively immunized by intraperitoneal injection at the time of experimental infection, or at various periods after experimental infection. Passive immunization of brook trout against furunculosis was therapeutically efficacious when effected either at zero, 24 or 48h post-infection, but not at 72 or 96h. Purified rabbit immunoglobulins specific to virulent A. salmonicida were as protective as the initial rabbit hyperimmune serum in protecting brook trout against furunculosis. To determine the prophylactic efficacy of this treatment, the groups of fish passively immunized at the time of the experimental infection were challenged a second time at either 14, 35, 41 or 56 days after passive immunization. Brook trout were protected against a second experimental bath challenge with virulent A. salmonicida for a period of 35–41 days.  相似文献   

12.
Abstract. This study evaluated four methods to establish asymptomatic carriers of Aeromonas salmonicida. Exposure of chinook salmon, Oncorhynchus tshawytscha (Walbaum), to A. salmonicida by gastric intubation resulted in a carrier prevalence of 65%. This prevalence was significantly higher than prevalences of 40, 20 and 10% after exposure respectively to broth culture bath, ingestion of broth coated feed, and exposure to intraperitoneally infected fish.  相似文献   

13.
Abstract. Strains of Aeromonas salmonicida subsp. salmonicida , the agent of furunculosis disease of salmonid fish, have fairly uniform plasmid patterns. Of 35 strains examined by agarose gel electrophoresis, 28 had a pattern consisting of four small plasmids (4.2, 3.6, 3.5, 3.3 Mda) and a larger plasmid. The larger plasmid was most often 50–56 Mda, but it was larger in some strains. In the remaining seven strains, the same general profile was seen, but one of the small plasmids was missing. An additional plasmid was present in six strains. The pattern seen in 30 strains collected from Ontario fish over an 8-year period did not differ significantly from five reference isolates from other locations. Plasmid profiles of A. salmonicida strains appear too uniform to provide a useful epidemiological tool. The non-pigmented. atypical strains of A. salmonicida subsp. achromogenes and A. salmonicida subsp. masoucida, A. media , and brown-pigmented strains of A. hydrophila had different plasmid DNA profiles, which were distinct from those of typical isolates of A. salmonicida subsp. salmonicida . Antibiotic susceptibility patterns, determined by the agar dilution method, were uniform for most typical strains. A non-transferable resistance to tetracyclmes was found in two Ontario isolates, but antibiotic resistance was relatively uncommon among the Ontario isolates.  相似文献   

14.
Experimental infections with Piscirickettsia salmonis via intraperitoneal (IP), oral (PO) and gill (GS) routes were compared, and the importance of physical contact in the horizontal transmission of this organism was investigated. Atlantic salmon, Salmo salar L., under-yearling parr raised in fresh water were used in this study. Samples of liver, kidney, spleen, gill and brain were collected weekly for 5 weeks after challenge, and were examined using the indirect fluorescent-antibody technique (IFAT). The pathogen was transmitted horizontally to fish with and without physical contact. However, transmission of P. salmonis occurred significantly more rapidly among fish with physical contact. Mortalities occurred in 50% of fish experimentally challenged with P. salmonis and their cohabitants. The estimates of the relative risk of dying demonstrated that fish challenged by the IP and GS routes had a significantly higher probability of dying than fish challenged by the PO route ( P < 0.005). Contact cohabitants with infected fish had a higher probability of death than non-contact cohabitants ( P < 0.005). The sequential studying using IFAT indicated that a haematogenous pattern of infection occurred among fish infected by oral and gill routes, or by cohabitation. This was different from the capsular (serosal) infection pattern observed in intraperitoneally inoculated fish. Piscirickettsia salmonis was observed within the cytoplasm of leucocytes and renal tubules, the latter indicating that elimination of this pathogen through the urine may be possible. Aeromonas salmonicida was also detected (by IFAT) in some of the fish exposed to P. salmonis , suggesting that P. salmonis may cause immunosuppression, and thus, increase the susceptibility of the host to other pathogens.  相似文献   

15.
Abstract. The host-parasite relationship between O-group carp and the ciliatc Ichthyophthirius multifiliis Fouquet was investigated, with the specific aim of characterizing the fate of parasites encountering immunized fish. Carp were immunized by repeated controlled infections; immunized fish and control fish naive to I. multifiliis were then infected in the caudal fin epidermis by a single controlled exposure to theronts, which were applied in a droplet suspension to the tail surface. The number of parasites present within the caudal fin was monitored over a subsequent 5-day period by means of in situ parasite mapping. Results indicated that, contrary to previous reports, theronts penetrated the skin of immunized fish in numbers comparable to those of fish receiving a primary infection. However, the majority of parasites which penetrated immune skin did not complete normal development; 79% of the parasites which had initially penetrated the immune skin were not relocated within 2h of exposure, and since no parasite material was detected at penetration sites, it was concluded that these parasites had prematurely exited the skin rather than been killed in situ. Subsequently, these sites became populated by leucocytes, predominantly macrophages, and the infiltrations continued for up to 5 days after the initial exposure. In contrast, at sites where mature trophonts had exited the skin of fish following a primary infection, more diffuse leucocytic infiltrations were recorded, and these were predominated by neutrophils. Differences in the response to parasite exit from immunized and previously unexposed control fish skin are discussed, with particular reference to the mode of protection and the fate of parasites encountering immune fish.  相似文献   

16.
The health status of eight marine rainbow trout farms was followed from mid-June to mid-September 2006 by sampling both dead and healthy fish approximately every 2 weeks for bacteriological and virological investigation. No fish pathogenic viruses were detected, but all farms experienced disease and mortality as a result of various bacterial infections. Yersinia ruckeri was found on four and Renibacterium salmoninarum on five of the farms, but only during the first part of the surveillance period. This indicates that the fish carried the infection from fresh water, and cleared the infection in salt water. Aeromonas salmonicida subsp. salmonicida caused mortality on five farms, but persisted throughout the sampling period. Although A. salmonicida was probably carried from fresh water, the fish were not able to clear the infection in the sea. Vibrio anguillarum caused mortality on six of the farms throughout the sampling period, O1 being the dominant serovar, and Photobacterium damselae subsp. damselae was found on seven farms as a cause of disease. During the period of highest water temperatures Vibrio parahaemolyticus and Vibrio vulnificus were detected in dead fish in five and two farms, respectively, although their significance as causative pathogens is questionable. Vibrio vulnificus has not previously been found in rainbow trout in Denmark. Both mortality and number of antimicrobial treatments during the period were considerably higher in unvaccinated compared with vaccinated fish. Resistance to commonly used antimicrobials was low or absent.  相似文献   

17.
Abstract. Infection trials using two serotypes of VHS viruses (type 1 and 23/75) demonstrated that Atlantic salmon fry were susceptible to the disease when injected intraperitoneally (i.p.) with 103 pfu of virus/fish but resistant to infection by a bath method when exposed for 3 h in water containing 5 × 104 pfu of virus/ml. In the i.p.-infected fish, mortality reached 78 and 67% within 13 days with VHSV1 nad 23/75 serotypes, respectively. High virus yields were recovered from infected fish and virus shedding was demonstrated by the onset of VHS in rainbow trout kept in the outflow water from the aquaria containing infected salmon. Neither mortality nor virus shedding occurred in salmon infected by the water route but virus multiplication was demonstrated in 2 of 60 fish with VHSV1 and 3 of 60 fish with virus 23/75. On day 79 post-infection the sera from surviving salmon of both i.p. and bath infection trials exhibited good neutralizing titres (around 1000) against the homologous viruses.  相似文献   

18.
The natural route by which fish become infected with mycobacteria is unknown. Danio rerio (Hamilton) were exposed by bath immersion and intubation to Mycobacterium marinum and Mycobacterium peregrinum isolates obtained from diseased zebrafish. Exposed fish were collected over the course of 8 weeks and examined for the presence of mycobacteriosis. Mycobacteria were consistently cultured from the intestines, and often from the livers and spleens of fish exposed by both methods. Mycobacteria were not observed in the gills. Histological analysis revealed that fish infected with M. marinum often developed granulomas accompanied by clinical signs of mycobacteriosis, while infection with M. peregrinum infrequently led to clinical signs of disease. Passage of the bacteria through environmental amoebae (Acanthamoeba castellani) was associated with increased growth of M. peregrinum over the course of 8 weeks, when compared to infection with the bacteria not passed through amoebae. The results provide evidence that zebrafish acquire mycobacteria primarily through the intestinal tract, resulting in mycobacterial dissemination.  相似文献   

19.
Hungary is an important carp producer with intensive trading relationships with farms in other carp‐producing areas in Europe. Carp in Europe were recently found infected with carp edema virus (CEV), a poxvirus which causes the koi sleepy disease (KSD) syndrome. Moribund carp were collected from 17 fish farms and angling ponds in different regions of Hungary. Histological analysis of gills from these carp revealed a proliferation of the interlamellar epithelium and an infiltration by eosinophilic cells. In 13 of 17 of these carp, CEV DNA was detected by qPCR and in seven fish more than 1 × 104 copies of virus‐specific DNA sequences per 250 ng of DNA, which could be considered as clinically relevant and a cause of disease. A phylogenetic analysis of the sequences revealed that all three genogroups of CEV were present in Hungarian common carp with genogroup I being most abundant. These results support the hypothesis of a prolonged presence of CEV in European carp populations and suggest that previous outbreaks of KSD were not recorded or misdiagnosed. Hence, a testing of carp and koi for infection with CEV should be included into disease surveillance programmes to prevent further spreading of this disease.  相似文献   

20.
Abstract. The survival of Aeromonas salmonicida subsp. salmonicida was investigated in sea water under a variety of conditions. Survival in different types of microcosms (glass or dialysis bags); of bacteria grown under both in vivo and in vitro (broth culture) conditions; and in sterile and non-sterile sea water were compared. In all cases, survival was found to be of short duration (<10 days) and did not conflict with the previously stated obligate nature of the pathogen. The spread of furunculosis may depend less on its ability to survive in the environment than on its rate of shedding from infected fish and prevailing hydrographic conditions. Survival was extended and growth occurred in sterile sea water to which nutrients (tryptone soya broth) had been added. However, sea water obtained from beneath a commercial salmon cage, which would have been expected to be nutrient rich, did not prolong the survival of the pathogen. In vivo infectivity studies provided no evidence for the existence of unculturable but infective forms of A. salmonicida subsp. salmonicida which, therefore, validates the use of colony-forming units as a measure of survival.  相似文献   

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