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The use of oral boosters as an alternative to control Piscirickettsia salmonis in farmed salmon in Chile

Fernando O. Mardones1, Jaime A. Tobar2*, Julio Mendoza3, Cristian Uribe3 and Eduardo Neira2
  • 1 Universidad Andres Bello, Veterinary Medicine, Chile
  • 2 Virbac-Centrovet, Chile
  • 3 Cermaq Chile, Chile

Piscirickettsia salmonis is a bacterium that causes piscirickettsiosis (SRS) in farmed salmon, the most important infectious disease in the Chilean salmon industry. SRS is difficult to prevent and control, causing large mortalities and increased production costs. Most farmers administer injectable vaccination in pre-smolts prior to transfer to seawater, where P. salmonis survives. However, injectable vaccinations do not last the entire farming period and antibiotics treatments are the single alternative to control the disease with variable response. Thus, alternative control measures are needed to control the disease, such as the use of oral boosters in seawater through feed, which can extent the immunity conferred by the first injectable vaccination. In this study, we evaluated the effect of the no use of booster, and the use of 1 to 3 consecutive boosters with the time to first SRS-mortality (T2SRS) and the SRS-specific cumulative mortality (cumSRS) at the end of the production cycle. Information was provided from 222 cages from 12 sea sites from a salmon company from 2013-2014, and analysis included Cox proportional hazards model to evaluate T2SRS, and mixed effects logistic regression to evaluate a dichotomous cumSRS. Median and mean cumSRS were 0.013% and 0.09%, respectively. T2SRS was 151 days (95% CI = 127-172) post transferred to seawater. Accordingly, the use of at least one booster delayed the appearance of the SRS mortality between 41 and 92 days compared to the no use (Fig. 1). The maximum difference was found when using 3 boosters that delayed SRS from 145 to 245 days compared to the no use; however, no differences where found when comparing T2SRS between the 2nd and 3rd booster. Comparing cumSRS it was found that at all degrees-days evaluated, mortalities associated with the use of 2 boosters were significantly lower than the no use (p=0.046), resulting in an important protection factor (Odds Ratio = 0.002, 95% CI = 0-0.9). It was also found that fish average weight at stock was a significant risk factor (OR = 1.32, 95% CI = 1.05-1.67). Predicted probabilities indicated that best results (reduced cumSRS) would be associated when administering 2 and 3 oral boosters for lighter fish. Results from this study demonstrated the positive effects of the use of boosters and the significant delay in the appearance of SRS at a cage level. In addition, the use of boosters showed significant associations with reduced cumSRS. The superior and extended protection offered by booster vaccination is noteworthy and may be applied in future sanitary strategies at cage or farm level to control SRS.

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Keywords: Piscirickettsia salmonis, SRS, Immunization, Vaccine, Booster, Disease control

Conference: AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.

Presentation Type: Oral

Topic: Aquatic Animal Epidemiology

Citation: Mardones FO, Tobar JA, Mendoza J, Uribe C and Neira E (2016). The use of oral boosters as an alternative to control Piscirickettsia salmonis in farmed salmon in Chile. Front. Vet. Sci. Conference Abstract: AquaEpi I - 2016. doi: 10.3389/conf.FVETS.2016.02.00027

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Received: 30 May 2016; Published Online: 14 Sep 2016.

* Correspondence: Dr. Jaime A Tobar, Virbac-Centrovet, Santiago, Chile, jtobar@centrovet.com