A comparative study on the effect of two inactivated Nocardia seriolae vaccine immunization methods in pearl gentian grouper

Abstract

Abstract In recent years, Nocardia seriolae has emerged as the main pathogen causing Nocardia disease in fishes. Fishes are infected with this pathogen through their gills and wounds. The infected fishes are characterized by a dark body color; occasional skin ulceration; and nodular lesions in the kidney, liver, heart, and other organs with a typical granuloma structure observed under a light microscope. In this study, a N. seriolae oral microsphere vaccine was prepared using sodium alginate, a natural polymer, as the envelope and N. seriolae inactivated vaccine as the inner core. Formalin-inactivated N. seriolae was used for the preparation of an injectable vaccine for conducting immune experiment that can compare immunization effects of the two vaccines. Test fish were randomly divided into three groups: injection group, oral vaccine group, and control group. After the immunization experiment, the vaccine protection rate in the groupers was measured, and the expression of the related immune genes was evaluated via Reverse Transcription-Polymerase Chain Reaction. The results indicated that the expression levels of TLR2, MyD88, TNF-α, and IL-12p40 were significantly increased in the spleen, liver, and kidney of the vaccinated fishes. The relative percentage of survival of the oral vaccine and injection groups was 62.5% and 70.5%, respectively. The results of this study provided insights on the methods to prevent and control N. seriolae disease and the development of a vaccine against it.