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

Schisandrin A: A sustainable antiviral and immunomodulatory agent against spring viraemia of carp virus in aquaculture

Spring viraemia of carp virus (SVCV) is a major threat to the aquaculture industry, causing severe economic losses and significantly impacting fish health. Despite this, no approved antiviral treatments are currently available for use in aquaculture, underscoring the urgent need for effective interventions. This study evaluated the antiviral and immunomodulatory potential of Schisandrin A (SA), a bioactive compound derived from the traditional Chinese medicinal herb Schisandra chinensis, against SVCV. Through a combination of in vitro and in vivo experiments, SA was found to significantly inhibit SVCV replication, lower the viral titer, and improve survival rates in infected juvenile carp. Mechanistically, SA enhanced the host's innate immune response, as demonstrated by the upregulation of key antiviral genes including interferon-alpha1 (ifna1), interferon-gamma (ifnγ), interferon-stimulated gene 15 (isg15), and myxovirus resistance 1 (mx1). Additionally, SA exhibited potent antioxidative properties, preserving mitochondrial integrity and reducing oxidative stress in SVCV-infected cells. These findings showed the dual role of SA in both directly suppressing viral replication and modulating the immune response, offering a multifaceted approach to managing SVCV infection. Given its low toxicity and biodegradability, SA emerges as a promising, sustainable antiviral agent for aquaculture. This study highlights the potential of SA to enhance biosecurity and promote sustainability in the industry, paving the way for the development of eco-friendly antivirals that could improve the management of viral diseases, ensuring healthier fish populations and greater economic stability.

Isopods infesting Atlantic bonefish (Albula vulpes) host novel viruses, including reoviruses related to global pathogens, and opportunistically feed on humans

Isopods infest fish worldwide, but their role as disease vectors remains poorly understood. Here, we describe infestation of Atlantic bonefish (Albula vulpes) in Belize with isopods in two of three locations studied, with infestation rates of 15 and 44%. Isopods fed aggressively, and infested fish showed missing scales and scars. Gross morphologic and molecular phylogenetic analyses revealed the isopods to cluster within the family Aegidae and to be most closely related to members of the genus Rocinela, which are globally distributed micro-predators of fish. Metagenomic analysis of 10 isopods identified 11 viruses, including two novel reoviruses (Reovirales) in the families Sedoreoviridae and Spinareoviridae. The novel sedoreovirus clustered phylogenetically within an invertebrate-specific clade of viruses related to the genus Orbivirus, which contains arboviruses of global concern for mammal health. The novel spinareovirus clustered within the fish-infecting genus Aquareovirus, which contains viruses of global concern for fish health. Metagenomic analyses revealed no evidence of infection of bonefish with the novel aquareovirus, suggesting that viremia in bonefish is absent, low, or transient, or that isopods may have acquired the virus from other fish. During field collections, isopods aggressively bit humans, and blood meal analysis confirmed that isopods had fed on bonefish, other fish, and humans. Vector-borne transmission may be an underappreciated mechanism for aquareovirus transmission and for virus host switching between fish and other species, which has been inferred across viral families from studies of deep virus evolution.

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.