A field study on intraperitoneal vaccination of Atlantic salmon (Salmo salarL.) against furunculosis

Protection and side-effects after intraperitoneal (i.p.) vaccination of Atlantic salmon (Salmo salarL.) against furunculosis were studied in a field trial. Pre-smolts held in fresh water and salmon growers held in sea water were immunised with different monovalent furunculosis vaccines. In both cohorts, disease attack rates and cumulative mortalities after field challenge were significantly lower in populations given a mineral oil adjuvanted vaccine compared to other vaccination groups included in the study, demonstrating that tentatively pathogen-free as well as furunculosis carrier populations can be protected by vaccination. Injection-site lesions of significance for the commercial quality of harvested salmon were observed, being more severe in fish given the mineral oil adjuvanted vaccine. In spite of the side-effects, i.p. vaccination with mineral oil adjuvanted vaccine is strongly recommended for effective furunculosis prophylaxis in commercial farming of Atlantic salmon.     

Distribution and retention of antigens of Aeromonas salmonicida in Atlantic salmon (Salmo salar L.) vaccinated with a DeltaaroA mutant or formalin-inactivated bacteria in oil-adjuvant

In this study we report the differences in distribution and retention of Aeromonas salmonicida antigens after vaccination with two different vaccines. Parr of Atlantic salmon (Salmo salar) were given intraperitoneal injections of either a commercial, monovalent furunculosis vaccine (Apoject) or live, attenuated A. salmonicida (DeltaaroA). Fish were sampled at weeks 2, 4 and 12 post-vaccination and head kidney and spleen were collected. Presence of LPS and 16S rDNA in isolated leukocytes were investigated by immunocytochemistry and polymerase chain reaction (PCR).16S rDNA was detected in head kidney and spleen of all DeltaaroA vaccinated and most Apoject-vaccinated fish at weeks 2 and 4. At week 12, 16S rDNA was detected in none of the DeltaaroA vaccinated fish, but it was detected in head kidney of 75% of Apoject-vaccinated fish. LPS was detected in both vaccination groups at all sampling times, but most frequently in the DeltaaroA vaccinated fish (in head kidney 75-83% vs. 50%, in spleen 58-67% vs. 17-25%).     

Naked DNA vaccination of Atlantic salmon Salmo salar against IHNV

A naked plasmid DNA encoding the glycoprotein (pCMV4-G) of a 1976 isolate of infectious hematopoietic necrosis virus (IHNV) obtained from steelhead Oncorhynchus mykiss was used to vaccinate Atlantic salmon Salmo salar against IHNV. Eight weeks post-vaccination the fish were challenged with a strain of IHNV originally isolated from farmed Atlantic salmon undergoing an epizootic. Fish injected with the glycoprotein-encoding plasmid were significantly (p < 0.05) protected against IHNV by both immersion and cohabitation challenge. Survivors of the first challenges were pooled and re-challenged by immersion 12 wk after the initial challenge. Significant (p < 0.05) protection was observed in all of the previously challenged groups including those receiving the complete vaccine. Fish injected with the glycoprotein-encoding plasmid produced low levels of virus-neutralizing antibodies prior to the first challenge. Neutralizing antibodies increased in all groups after exposure to the IHNV. Passive transfer of pooled sera from pCMV4-G vaccinates and IHN survivors provided relative survivals of 40 to 100% compared to fish injected with sera collected from fish immunized with control vaccines or left unhandled. In this study, DNA vaccination effectively protected Atlantic salmon smolts against challenges with IHNV.     

Salmonid alphavirus-based replicon vaccine against infectious salmon anemia (ISA): Impact of immunization route and interactions of the replicon vector

A salmonid alphavirus (SAV)-based replicon encoding the infectious salmon anemia virus (ISAV) hemagglutinin-esterase (HE), pSAV/HE, is an efficacious vaccine against infectious salmon anemia (ISA). Delivered intramuscularly (i.m.), the replicon vaccine provides high protection against subsequent ISAV challenge in Atlantic salmon (Salmo salar), and induces a strong innate response locally at the injection site. This may be beneficial and could warrant reduced doses and improved efficacy compared to conventional DNA vaccines. In the present study, we found that intraperitoneal (i.p.) administration of the pSAV/HE replicon vaccine did not induce protection, neither alone or in combination with a sub-potent, inactivated low-dose ISAV vaccine given i.p. No significant differences between the two immunization routes regarding systemic immune responses could be observed. I.m. injection of the replicon vector encoding a non-viral gene or the protective glycoprotein (G protein) from the heterologous viral hemorrhagic septicemia virus (VHSV) induced no protection against ISA. Although the replicons without the ISAV HE did induce IFN-signaling pathways at the muscle injection site similar to the pSAV/HE replicon they did not improve the efficacy of a sub-potent inactivated low-dose ISAV vaccine delivered i.p. Moreover, there was a tendency for reduced efficacy of the pSAV/HE replicon vaccine injected i.m. when co-injected with the replicon encoding the VHSV G protein, which previously, after DNA vaccination, have been reported to induce cross-protection against heterologous virus challenge in fish.     

Evaluation of a whole cell, p57- vaccine against Renibacterium salmoninarum.

A whole cell Renibacterium salmoninarum vaccine was developed using 37 degrees C heat treated cells that were subsequently formalin fixed; this treatment reduced bacterial hydrophobicity and cell associated p57. Coho salmon Oncorhynchus kisutch were immunized with the p57- vaccine by either a combination of intraperitoneal (i.p.) and intramuscular (i.m.) injections or per os. In the first experiment, i.p./i.m. vaccination of coho salmon with p57- cells in Freund's Incomplete Adjuvant (FIA) conferred a statistically significant increase in mean time to death after the salmon were i.p. challenged with 4.1 x 10(6) colony forming units (cfu) of R. salmoninarum. There was no significant difference in response between fish immunized with R. salmoninarum cell surface extract in FIA and those immunized with extracellular protein (ECP) concentrated from culture supernatant in FIA. The i.p. challenge dose resulted in complete mortality of all fish by Day 43. In a second experiment, fish were orally vaccinated with p57- R. salmoninarum cells encased in a pH protected, enteric-coated antigen microsphere (ECAM). Fish were bath challenged with 4.2 x 10(6) cfu ml-1 on Day 0 and sampled at time points of 0 (pre-challenge), 50, 90, or 150 d immersion challenge. Vaccine efficacy was determined by monitoring the elaboration of p57 in the kidneys of vaccinated and control fish. Fish vaccinated orally demonstrated a significantly lower concentration of p57 (p < 0.01) at Day 150 post challenge compared to fish receiving ECAMs alone. Fish receiving p57 cells without ECAM coating also showed a significantly lower p57 level (p < 0.03) versus control. In contrast, fish injected intraperitoneally with the p57- cells or fish fed p57+ R. salmoninarum cells in ECAMs demonstrated no significant difference (p > 0.05) versus controls. In summary, these studies suggest the preliminary efficacy of 37 degrees C treatment of R. salmoninarum cells as an oral bacterial kidney disease vaccine.     

Development of an antibody ELISA for potency testing of furunculosis (Aeromonas salmonicida subsp salmonicida) vaccines in Atlantic salmon (Salmo salar L)

The study was conducted in Atlantic salmon to establish the initial and basic scientific documentation for an alternative batch potency test for salmon furuculosis vaccines. We assessed the antibody response development for Aeromonas salmonicida vaccines at different immunisation temperatures (3, 12 and 18 °C), by an enzyme-linked-immunosorbent assay (ELISA) 3, 6, 9 and 12 weeks post vaccination, and the correlation between antibody response and protection in cohabitation challenge experiments performed 6 and 12 weeks post vaccination. Fish immunised with a vaccine containing full antigen dose had a significant increase in antibody response after 252 day degrees and the measured values correlated well with protection after 500 day degrees. Fish vaccinated with a reduced antigen dose showed a significant lower antibody response than fish vaccinated with the full dose vaccine at all samplings, and showed a similar low relative percent survival (RPS) in the challenges. The results from this study indicate that an antibody ELISA can discriminate between vaccines of different antigen content and the method may replace challenge tests in batch potency testing of furunculosis vaccines in Atlantic salmon. An immunisation temperature of 12 °C and sampling after 6-9 weeks, seemed to be the most appropriate time for using antibody responses to confirm batch potency.     

Isolation of salmon pancreas disease virus (SPDV) in cell culture and its ability to protect against infection by the 'wild-type' agent

A Scottish salmon pancreas disease virus (SPDV) has been isolated and its optimum growth conditions determined. Although several fish cell lines have been tested, successful culture was achieved only with CHSE-214 cells. Cytopathic effects were observed after 5 days. The highest virus titres, calculated by microtitration assay, were reached at 15 degrees C. After 7-9 days post-inoculation, CHSE-214 cell supernatants contained between 10(7)-10(5) TCID50 ml(-1) The cultured isolate is chloroform- and pH 3.0-sensitive, and virions are 50-60 nm in diameter. These characteristics are similar to the Irish SPDV isolates. The culture isolate induced typical pancreas disease (PD) lesions in experimentally infected Atlantic salmon and convalescent fish were resistant to experimental infection with PD-infective kidney homogenates obtained by serial in vivo passages from a PD-infected farmed salmon (termed wild-type SPDV). Furthermore, fish immunised with the inactivated cultured virus were protected against a cohabitation challenge with the wild-type virus. Immunised fish sera showed virus-neutralising activity before challenge (7 weeks post-immunisation) and from 3-6 weeks post-challenge, when sera from non-immunised fish did not neutralise the virus. At 6 weeks post-cohabitation challenge, previously immunised fish had neutralising titres of up to 1:65. Following intraperitoneal (i.p.) challenge, immunised fish showed neutralising titres as high as 1:226 at 8 weeks post-challenge. Non-immunised fish injected i.p. with the wild-type virus developed serum-neutralising activity against the cultured isolate when sampled 8 weeks after infection, confirming an antigenic relationship between the wild-type and cultured virus. The results demonstrate that the tissue culture-adapted isolate of SPDV could be successfully used to protect against challenge by the wild-type virus and could therefore have potential use as an inactivated vaccine against PD.     

Quantitative genetics of disease resistance in vaccinated and unvaccinated Atlantic salmon (Salmo salar L.)

Furunculosis (Aeromonoas salmonicida) is an important disease in Atlantic salmon (Salmo salar) farming. Vaccination and selective breeding for increased resistance to the disease on the basis of challenge tests of unvaccinated fish are used as complementary prophylactic methods. An important issue is whether genetic predisposition to infection is consistent across vaccinated and unvaccinated fish. Hence, the main objective of this study was to determine the magnitude of the genetic associations (correlations) between resistance to furunculosis in vaccinated and unvaccinated fish, and to estimate the magnitude of the correlation of resistance to furunculosis with resistance to the viral diseases infectious pancreatic necrosis (IPN) and infectious salmon anaemia (ISA). Sub-samples of unvaccinated and vaccinated salmon from 150 full-sib families were subjected to separate cohabitation challenge tests. Substantial genetic variation was found in resistance to furunculosis in both the unvaccinated (heritabilities of 0.51 ± 0.05) and vaccinated (0.39 ± 0.06) fish. However, the genetic correlation between resistance to furunculosis in the two groups was low (0.32 ± 0.13), indicating a weak genetic association between resistance in the two groups. Hence, the current selection strategy on the basis of challenge tests of unvaccinated fish is likely to produce low genetic improvement in resistance to furunculosis under field conditions, where fish are vaccinated with an effective vaccine. Evidence was found of significantly favourable genetic associations of resistance to furunculosis in unvaccinated (but less so for vaccinated) fish with resistance to both IPN and ISA (unvaccinated fish), indicating that vaccination 'mask' genetic associations between resistance to different diseases.     

DNA vaccination against viral haemorrhagic septicaemia (VHS) in rainbow trout: size,dose, route of injection and duration of protection-early protection correlates with Mx expression

Rainbow trout of different sizes (10 and 100g) were injected intramuscularly (i.m.) or intraperitoneally (i.p.) with different doses (range 10 ng-10 microg) of a viral haemorrhagic septicaemia (VHS)-DNA vaccine (pcDNA3vhsG). As controls, fish were injected with the pcDNA3 plasmid alone, or with inactivated VHS virus. Fish were challenged at different times post-vaccination (p.v.) to assess protection. At certain times p.v., serum samples were analysed for neutralising antibody and liver tissue was analysed for Mx mRNA expression. A DNA dose of 0.5 microg injected by the i.m. route induced protection in fish of all sizes in challenges performed either 1 or 4 weeks p.v. This dose also conferred effective protection up to 9 months p.v. in fish >100 g. With lower doses of DNA (0.1 and 0.01 microg) and challenge at 4 weeks p.v., 10 g fish were partially protected but protection was not observed in 100 g fish. Vaccination by the i.p. route induced no or lower levels of protection compared with the i.m. route. Fish vaccinated with 0.5 microg DNA i.m. had no detectable serum neutralising antibody (NAb) at 4 weeks p.v. (with the exception of a single 10 g fish) but antibody was detected at 8 weeks and 6 months p.v. but not at 9 months p.v. However, cohorts of these fish showed effective protection at all timepoints. Lack of detectable levels of NAb (at 9 weeks p.v.) despite partial protection in challenge at 4 weeks p.v. was also observed with 0.01 microg doses of DNA i.m. NAb was detected in sera of fish at 8 weeks after vaccination with 0.1 microg i.m. but not in fish vaccinated with doses of 0.01-0.5 microg i.p. Early protection (1 week p.v.) correlated with elevated Mx gene expression.     

MHC polymorphism and disease resistance in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>); facing pathogens with single expressed major histocompatibility class I and class II loci

Few studies have yet addressed the functional aspects of MHC molecules in fish. To lay the foundation for this, we evaluated the association between disease resistance and MHC class I and class II polymorphism in Atlantic salmon. Standardized disease challenge trials were performed on a semi-wild Atlantic salmon population with subsequent MHC typing and statistical analysis. The pathogens employed were infectious salmon anaemia virus (ISAV) causing infectious salmon anaemia and the Aeromonas salmonicida bacteria causing furunculosis. The material consisted of 1,182 Atlantic salmon from 33 families challenged with A. salmonicida and 1,031 Atlantic salmon from 25 families challenged with ISAV. We found highly significant associations between resistance towards infectious diseases caused by both pathogens and MH class I and class II polymorphism in Atlantic salmon. The observed associations were detected due to independently segregating MH class I and class II single loci, and inclusion of a large number of fish allowing an extensive statistical analysis.     

Reduction ofRenibacterium salmoninarumculture activity in Atlantic salmon following vaccination with avirulent strains

A series of challenge experiments were conducted to determine the efficacy of vaccination against bacterial kidney disease (BKD) in Atlantic salmon using an avirulent mutant ofRenibacterium salmoninarum(RsTSA I), and a related Gram-positive bacterium (Rsx II). Vaccination had a pronounced effect on the presence of the pathogen in fish kidney tissue. At 14 weeks after infection, the relative percentage of fish which were culture negative forR. salmoninarumwas 69·0 and 81·2 respectively for the two strains compared to 85·8% culture positive for the unvaccinated control group. Furthermore the use of a polymerase chain reaction (PCR) test to detectR. salmoninarumbeing shed from the asymptomatic fish clearly identified the pathogen in water from tanks containing the unvaccinated group but not from water taken from the tanks vaccinated with either of the vaccine strains.     

Vaccine efficacy in spotted wolffish Anarhichas minor: relationship to molecular variation in A-layer protein of atypical Aeromonas salmonicida

Atypical Aeromonas salmonicida strains comprise a heterogeneous group in terms of molecular and phenotypic characteristics. They cause various conditions of ulcer diseases or atypical furunculosis and are being isolated in increasing number from various fish species and geographical areas. Several marine fish species susceptible to atypical A. salmonicida, including spotted wolffish Anarhichas minor O., are now being farmed and new vaccines may be needed. A commercial furunculosis vaccine for salmon is reported to protect wolffish poorly against experimental challenge with atypical A. salmonicida. The protective antigen(s) in furunculosis vaccines is still unclear, but in oil-adjuvanted vaccine for Atlantic salmon Salmo salar L., the surface A-layer was shown to be important for protection. In spotted wolffish, the efficacy of atypical furunculosis vaccines seems to vary with the atypical A. salmonicida strains used as bacterin in the vaccine. In the present study we investigated whether differences in the A-layer protein among atypical strains might be responsible for the observed variation in vaccine efficacy. Atypical A. salmonicida strains from 16 fish species in 11 countries were compared by genome polymorphism analysis using amplified fragment length polymorphism (AFLP) fingerprinting and by comparative sequencing of the vapA genes encoding the A-protein. The A-protein sequences appeared to be highly conserved except for a variable region between Residues 90 to 170. Surprisingly, the grouping of strains based on AFLP- or A-protein sequence similarities was consistent. In addition, serological differences in the A-protein among the strains were demonstrated by an A-protein-specific monoclonal antibody. Vaccines based on atypical A. salmonicida strains possessing genetically and serologically different A-layer proteins were shown to result in significantly different protection in spotted wolffish.     

Expression kinetics of interferon and interferon-induced genes in Atlantic salmon (Salmo salar) following infection with infectious pancreatic necrosis virus and infectious salmon anaemia virus

Infectious pancreatic necrosis virus (IPNV) and infectious salmon anaemia virus (ISAV) are economically important pathogens of the salmonid aquaculture industry. Atlantic salmon were challenged by intraperitoneal injection (i.p.) with either virus followed by time-course sampling. Cohabiting fish in the IPNV challenge were also sampled. Kidney tissue was analysed using a TaqMan real-time PCR assay to measure the expression of a range of host immune genes in relation to the endogenous control, elongation factor 1 alpha (ELF). Host genes measured included Mx, type I and type II interferon (IFN), gammaIFN induced protein (gammaIP), interleukin-1 beta (IL-1beta) and tumour necrosis factor alpha (TNF-alpha). Viral levels were also measured. In i.p. injected fish, both viruses greatly induced expression of Mx, gammaIP, type I and type II IFN by day 6 post-infection, however only ISAV caused substantial mortality. Some differences between the expression kinetics produced by both viruses were noted. Infection with ISAV increased IL-1beta expression following day 6, but no effect was seen in fish infected with IPNV. Neither virus induced TNF-alpha expression. This study confirms the presence of both type I and type II IFN responses and their induced genes in Atlantic salmon upon infection with an orthomyxovirus and a birnavirus.     

Efficacy of a bivalent vaccine against eel diseases caused by Vibrio vulnificus after its administration by four different routes

Vulnivaccine, a vaccine against vibriosis caused by Vibrio vulnificus serovar E (formerly biotype 2), confers acceptable levels of protection to eels after its administration by prolonged immersion in three doses. Recently, a new pathogenic serovar, named serovar A, has been isolated from vaccinated eels in a Spanish freshwater eel farm. The main objective of this work was to design a bivalent vaccine, and to study its effectiveness against the two pathogenic serovars. With this aim, eels weighing around 20 g were immunised with the bivalent vaccine by oral and anal intubation, intraperitoneal injection (i.p.) and prolonged immersion. The overall results indicated that: (i) the new vaccine delivered by oral and anal intubation induced protection levels higher than 80%, to that achieved after i.p. vaccination; (ii) oral and anal vaccination induced a significant systemic and mucosal immune response; (iii) the protection after vaccination by whichever routes was related to antibody titres in plasma; (iv) mucosal and systemic compartments showed different kinetics of antibody production; (v) evidence for passive transfer of antibodies from plasma to gut mucus were found after i.p. and anal vaccination, and finally, (vi) vaccination did not enhance the production of lysozyme, in plasma or mucus. In conclusion, this new vaccine is effective in protecting eels against vibriosis caused by the two eel-pathogenic serovars of V. vulnificus, the oral delivery system is a promising way which may be used in intensive culture facilities during the whole growth period of eels.     

Development of an effective Edwardsiella tarda vaccine for cultured turbot (Scophthalmus maximus)

Since 2004 Edwardsiella tarda has become one of the most important emerging pathogens in turbot aquaculture industry in Europe causing serious economic losses. Therefore, this study aimed to design an effective vaccination strategy to prevent edwardsiellosis in this fish species. Two vaccine formulations, an adjuvanted vaccine and an aqueous bacterin, and different routes of administration, bath and intraperitoneal injection (i.p.), were tested. The effectiveness of the different immunization strategies was evaluated in terms of relative percent survival (RPS) and antibody levels. On the basis of the results obtained we recommend the i.p. administration of a non-mineral oil adjuvanted vaccine via i.p., which confers RPS values over 90% at least 6months post-vaccination.     

The effect of vaccination and sea water entry on immunocompetence and susceptibility to Kudoa thyrsites in Atlantic salmon (Salmo salar L.)

The effect of intraperitoneal (IP) vaccination and sea water entry (SWE) on the immunocompetence of Cascade Atlantic salmon was investigated. Smolts were IP injected with Aqua Health's Forte trade mark vaccine (Listonella (Vibrio) anguillarum, Listonella ordalii, Vibrio salmonicida and Aeromonas salmonicida) at four times (42, 238, 433 and 630 degree days, DD) prior to SWE and were examined for immunocompetence. Immune response measurements included mitogen-driven proliferation of peripheral blood leukocytes (PBL), head kidney leukocyte respiratory burst activity and alternative complement hemolytic titres and were measured 24h prior to SWE, 72 h post-SWE and again 3.5 weeks post-SWE. A 50% reduction in the number of PBL was observed 3 days post-vaccination. At this time LPS-driven proliferation was low (stimulation index, SI, 1.5-2.9) in all groups prior to SWE compared with that of PBL from freshwater-reared Atlantic salmon parr (6.7). By 72 h and 3.5 weeks post-SWE, the LPS-driven SI from unvaccinated salmon and those vaccinated 630 and 433 DD prior to SWE increased 3-fold. In contrast, SI from salmon vaccinated 42 and 238 DD prior to SWE remained low. A similar pattern was observed for cultured PBL stimulated with PHA, although unlike LPS-stimulated PBL, the SI of cells from parr and unvaccinated control smolts remained low following SWE but increased in fish vaccinated 433 and 630 DD prior to SWE. The respiratory burst activity of head kidney leukocytes was not affected by SWE but showed a transient 50% depression 3 days post-vaccination. The alternative complement activity (ACH50) was similar for all treatment groups prior to and at 72h post-SWE. By 3.5 weeks post-SWE, ACH50 values in salmon vaccinated 42 and 238 DD prior to SWE doubled to 874 and 860 U/ml, respectively. The prevalence and severity of Kudoa thyrsites infections, detected in all treatment groups approximately 2400 DD following SWE, were not significantly different among groups. Atlantic salmon parr should be IP vaccinated no earlier than 433 DD before SWE to avoid an enhanced risk of acquiring pathogens because of transient depression in some immune mechanisms.     

Fish DNA vaccine against infectious hematopoietic necrosis virus: efficacy of various routes of immunisation

The DNA vaccine, pIHNVw-G, contains the gene for the glycoprotein (G) of the rhabdovirus infectious hematopoietic necrosis virus (IHNV), a major pathogen of salmon and trout. The relative efficacy of various routes of immunisation with pIHNVw-G was evaluated using 1.8 g rainbow trout fry vaccinated via intramuscular injection, scarification of the skin, intraperitoneal injection, intrabuccal administration, cutaneous particle bombardment using a gene gun, or immersion in water containing DNA vaccine-coated beads. Twenty-seven days after vaccination neutralising antibody titres were determined, and 2 days later groups of vaccinated and control unvaccinated fish were subjected to an IHNV immersion challenge. Results of the virus challenge showed that the intramuscular injection and the gene gun immunisation induced protective immunity in fry, while intraperitoneal injection provided partial protection. Neutralising antibodies were not detected in sera of vaccinated fish regardless of the route of immunisation used, suggesting that cell mediated immunity may be at least partially responsible for the observed protection.     

Vaccination of Atlantic salmon with recombinant VP2 of infectious pancreatic necrosis virus (IPNV), added to a multivalent vaccine, suppresses viral replication following IPNV challenge

Atlantic salmon (Salmo salar) pre-smolts vaccinated with Norvax^®Protect (NP) or injected with saline, were demonstrated to have a significantly (P≤0·0001) higher probability of being IPNV-infected when sampled during 12 weeks post challenge (PC) with IPNV (11·7 times and 32·5 times higher, respectively), than fish vaccinated with Norvax^®Protect-IPN (NP-IPN), a vaccine identical to NP except for the presence of recombinant VP2. Furthermore, following experimental challenge with IPNV, an IPNV-specific secondary humoral immune response was detected in the group vaccinated with NP-IPN. Statistical analysis revealed that NP-IPN-vaccinated fish had a significantly (P≤0·0001) higher probability of producing IPNV-specific antibodies during 12 weeks PC with IPNV, compared to NP-vaccinated or saline-injected fish (5·3 times and 7·6 times higher, respectively). The results support efficacy data from field trials in Norway, where NP-IPN has proven successful in the prevention of IPN in Atlantic salmon post-smolts. However, the immunological mechanisms behind the increased IPNV clearance remain unknown.     

Use of a live vaccine to modulate Cryptobia salmositica infections in Salmo salar

The vaccine strain of Cryptobia salmositica multiplies in Atlantic salmon Salmo salar and it can modulate the severity of the disease in Cryptobia-infected individuals. Fish injected with the vaccine 3 d post-infection with C. salmositica had lower peak parasitaemias and higher antibody titres than infected fish given the vaccine 7 d post-infection or those infected fish that were not given the vaccine.