Identification of Surrogates of Protection against Yersiniosis in Immersion Vaccinated Atlantic Salmon

Abstract

Simple cost-effective bacterins are the earliest and most successfully used commercial vaccines in fish. In particular, those prepared from Yersinia ruckeri have proven effective at controlling Enteric Red Mouth Disease (ERM) and yersiniosis in rainbow trout and Atlantic salmon, respectively. However, the emergence of outbreaks of ERM caused by atypical biotypes of Y. ruckeri and reports of vaccine failure resulting in mass mortality of hatchery Atlantic salmon has reinvigorated interest in vaccines against fish bacterial diseases. Therefore the objective of this study was to identify surrogates of protection against yersiniosis using cDNA microarray to characterise the response of host genes in the gills of unvaccinated and vaccinated Atlantic salmon challenged with Y. ruckeri. Differentially expressed genes were identified using two-way ANOVA and restricted to those with >2.5-fold change at P<0.05. Using cDNA microarray we identified the expression of 6 genes in response to infection and 4 genes associated with the protective host response to yersiniosis. Analysis by real-time PCR confirmed that three immunologically relevant genes, namely a cathelicidin (47-fold) and a C-type lectin (19-fold) increased in response to yersiniosis. Including collagenase (17-fold increase), an important tissue remodelling and repair enzyme, these genes represent 3 of 6 non-protective and/or pathological responses to yersiniosis. Genes associated with the protective host response included an immunoglobulin gene and a selenoprotein that showed significant fold changes (15-fold increases each), highlighting the importance of antibody-mediated protection against yersiniosis. These findings provide much needed knowledge of the host-pathogen interaction in response to bacterial infection and immunisation in fish. Significantly, we identified a transcriptional biosignature consisting of predominantly immune-relevant genes (14 up and 3 down-regulated) in the gills of Atlantic salmon after immersion vaccination and before bacterial challenge. This biosignature may be used as a surrogate of protection and therefore as a predictor of vaccine success against yersiniosis.

The adjuvant effect of low frequency ultrasound when applied with an inactivated Aeromonas salmonicida vaccine to rainbow trout (Oncorhynchus mykiss)

“…Interestingly, recent research has shown that an autologous immersion vaccine against A. salmonicida induces protection against furunculosis in rainbow trout [16], and that protection is not correlated with the production of systemic antibodies [15,16,30]. Supporting our study, were it may be that protection is achieved by mucosal protection through mucosal antibodies [18], lymphoid tissue [29] and other components [17] specifically found in mucosal tissue such as gills. In a previous pilot trial, high intensity sonophoresis achieved protection against A. salmonicida infection in goldfish [31].…”

“…Furthermore, it has recently been reported that immersion vaccination can fail to produce antibody titres in vaccinated fish that correlate with protection, although the vaccine still induces long term protection in the fish [16]. Thus, it should be considered that the protective response to the vaccine is not only be based on the production of systemic antibodies found in blood, but also on the mucosal protection found in fish gills [17,18].…”

Yersinia ruckeri Isolates Recovered from Diseased Atlantic Salmon (Salmo salar) in Scotland Are More Diverse than Those from Rainbow Trout (Oncorhynchus mykiss) and Represent Distinct Subpopulations

“…Vaccination has played an important role in controlling ERM/ yersiniosis in Atlantic salmon in Australia (50), Chile (9, 51), Norway (12), and Scotland. The vaccines used for Atlantic salmon are generally the same serotype O1-based vaccines as those used for rainbow trout (9,20), although, in Scotland, there has been a shift toward the use of multivalent autogenous vaccines in recent years (T. Wallis, Ridgeway Biologicals Ltd., personal communication).…”

Efficacy of a formalin-inactivated vaccine against Streptococcus iniae infection in the farmed grouper Epinephelus coioides by intraperitoneal immunization

“…Vaccine efficacy is usually evaluated through challenge experiments, which are time consuming and require many controls [36]. TNF-␣ has been proposed as a biomarker for monitoring fish health and vaccine efficacy [37,38].…”