Mucoadhesive chitosan-based nano vaccine as promising immersion vaccine against Edwardsiella tarda challenge in Nile tilapia (Oreochromis niloticus)

Immersion vaccination with a biomimetic mucoadhesive nanovaccine has been shown to induce a strong mucosal immune response against Edwardsiellosis, a serious bacterial disease in Nile tilapia caused by Edwardsiella tarda. This study aims to develop and investigate the efficacy of immersion delivery using a chitosan nano-vaccine (CS) with β-glucan (BG) as an adjuvant to enhance the mucoadhesive properties of the vaccine. The prepared vaccines were nano-sized and spherical as confirmed by scanning electron microscope (SEM), and the images show that nano vaccine greatly increased the binding and penetrating ability into gills when compared with formalin-killed vaccine. Fingerling-sized Nile tilapia (12 ± 2 g) were randomly assigned to four groups: control, Formalin Killed vaccine (Positive control), Chitosan/β-glucan alone (CS/BG), and Chitosan/β-glucan Vaccine (CS/BG V). Fish received immersion baths on days 1 and 21 with a 30-min booster dose. Samples were collected at two time intervals (14, and 28 days post-vaccination (Dpv)) to evaluate innate immune responses through lysozyme, myeloperoxidase, NBT, and superoxide dismutase activity were significantly elevated in vaccinated fish compared to the control group (p < 0.05). IgM antibody titers, measured by ELISA, peaked at 14 and 28Dpv compared to the non-vaccinated group. Furthermore, after vaccination, gene expression analysis using qRT-PCR showed a significant increase in IgM, TNF-α, IL-1β, TCR- β, MHC-I, and IL-8 in the spleen of CS/BG V fishes, with similar antibody responses observed. The efficacy of the vaccine was further assessed by challenging the fish with virulent E. tarda after 36 Dpv, and observed 15 days for cumulative mortality. The results demonstrate that the vaccine showed significant protection of 24.44 %, 37.78 %, 48.89 % and 68.89 % respectively, in groups and high relative percentage survival (RPS) in the C/BG V group compared to the control group. Histopathological examinations of head kidney, spleen, and gills were performed for all four groups showed mild infiltrations. This chitosan nano formulation, adjuvanted with a β-glucan immersion vaccine delivery method, will prove effective for Nile tilapia (Oreochromis niloticus), significantly impacting aquaculture and potentially being applicable against other pathogens in global aquaculture systems.