Abstract
Salmon rickettsial septicaemia (SRS) is the infectious disease that produces the highest losses in the Chilean salmon industry. As a new strategy for the control of SRS outbreaks, in this study we evaluated the effect of alginate-encapsulated Piscirickettsia salmonis antigens (AEPSA) incorporated in the feed as an oral vaccine to induce the immune response in Atlantic salmon (Salmo salar). Fish were distributed into three vaccination groups (injectable, oral high dose, oral low dose). Feed intake and fish growth were recorded during the trial. The P. salmonis-specific IgM levels in blood plasma were measured by ELISA. Alginate microparticles containing the antigen were effectively incorporated in fish feed to produce the oral vaccine. Incorporation of AEPSA did not affect the palatability of the feed or the fish appetite. Furthermore, the oral vaccine did not have a negative effect on fish growth. Finally, the oral vaccine (high and low dose) produced an acquired immune response (IgM) similar to the injectable vaccine, generating a statistically significant increase in the IgM levels at 840-degree days for both experimental groups. These findings suggest that AEPSA incorporated in the feed can be an effective alternative to boost the immune response in Atlantic salmon (S. salar).
Highlights
Salmon rickettsial septicaemia (SRS) is an infectious disease that affects salmon aquaculture around the world with a high economic impact [1]
Our study demonstrates that P. salmonis antigens can be microencapsulated in alginate using an aerodynamically assisted jetting system, generating small microparticles that can be incorporated into fish feed pellets and produce an oral vaccine
It was confirmed that the addition of alginate-encapsulated P. salmonis antigens (AEPSA) does not induce effects on the palatability of the feed and that oral vaccination does not affect the appetite of the fish
Summary
Salmon rickettsial septicaemia (SRS) is an infectious disease that affects salmon aquaculture around the world with a high economic impact [1]. SRS is responsible for 50% to 97% of the total disease-specific salmon mortality in the industry, accounting for annual direct and indirect loses between. The disease is caused by a non-motile obligate intracellular Gram-negative bacterium, Piscirickettsia salmonis, producing septicemia and high mortality in the fattening phase of Vaccines 2020, 8, 450; doi:10.3390/vaccines8030450 www.mdpi.com/journal/vaccines. Vaccines 2020, 8, 450 the fish [3]. This pathogen was initially isolated from Coho salmon (Oncorhynchus kisutch) in Chile and has since been reported in Canada, Ireland, Norway and Scotland [4]. Vaccines and antibiotics are used to prevent and treat bacterial infections. The use of antibiotics has not delivered the expected protection, leading to their excessive use, which could eventually lead to the development of drug resistance in bacteria [5]
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