Viral infections in cultured fish and shrimps: current status and treatment methods

Synbiotic Agents and Their Active Components for Sustainable Aquaculture: Concepts, Action Mechanisms, and Applications

Aquaculture is a fast-emerging food-producing sector in which fishery production plays an imperative socio-economic role, providing ample resources and tremendous potential worldwide. However, aquatic animals are exposed to the deterioration of the ecological environment and infection outbreaks, which represent significant issues nowadays. One of the reasons for these threats is the excessive use of antibiotics and synthetic drugs that have harmful impacts on the aquatic atmosphere. It is not surprising that functional and nature-based feed ingredients such as probiotics, prebiotics, postbiotics, and synbiotics have been developed as natural alternatives to sustain a healthy microbial environment in aquaculture. These functional feed additives possess several beneficial characteristics, including gut microbiota modulation, immune response reinforcement, resistance to pathogenic organisms, improved growth performance, and enhanced feed utilization in aquatic animals. Nevertheless, their mechanisms in modulating the immune system and gut microbiota in aquatic animals are largely unclear. This review discusses basic and current research advancements to fill research gaps and promote effective and healthy aquaculture production.

Recombinant surface display vaccine enhances the immersion immune effect against grass carp reovirus in grass carp (Ctenopharyngodon idella)

Grass carp (Ctenopharyngodon idella) is subject to a hemorrhagic disease caused by grass carp reovirus (GCRV), which can lead to mass mortality in grass carp culture, causing significant economic loss. Vaccination is the most promising strategy for the prevention of infectious diseases. Immersion vaccination is considered the most effective disease prevention method for juvenile fish because it can be implemented on many fish at once and administered without causing stress. However, immune responses by immersion vaccination are markedly less robust due to the skin barrier and insufficient antigen uptake. The display of heterologous proteins on the cell surface has been explored as a delivery system for viral antigens in veterinary and human vaccine studies. To improve the efficacy of the immersion vaccine, the major capsid protein (VP7) of GCRV was co-displayed with Aeromonas hydrophila outer membrane protein a (OmpA) and major adhesion protein (Mah) on the outer membrane surface of nonpathogenic Escherichia coli BL21 using the anchoring motif of ice-nucleation protein (Inp). The immune responses and protection efficiency against GCRV infection via both the injection and immersion routes were evaluated. The results indicated that the activities of anti-oxidant enzymes (ACP, AKP, SOD and T-AOC), as well as the expression of immune-related genes (TNF-α, IL-1β, MHCI and IgM) and specific VP7 antibody levels, were strongly increased in the grass carp from 7 to 21 days post-injection inoculation in a dose dependent manner. The cumulative mortality rates of injection-vaccinated groups were much lower than those of the control group after the GCRV challenge, and the relative percent survival (RPS) was greater than 80 %. Vitally, the surface co-display of vp7-Mah protein conferred marked protection to grass carp against GCRV infection after immersion administration (RPS >50 %); this was consistent with the production of high level of specific serum antibodies, non-specific immune responses, and the expression of immune-related genes. Moreover, the invasion analysis further showed that surface co-display of the vp7-Mah protein indeed significantly improved the invasion of E. coli BL21 (DE3) in vitro. Altogether, this study demonstrated that surface display GCRV core antigen vaccine system accompanied by invasion component from aquatic pathogenic microorganism is an effective prophylactic against GCRV viral diseases via the immersion administration approach.