Functional nutrition modulates the early immune response against viral haemorrhagic septicaemia virus (VHSV) in rainbow trout.

Although viruses represent a major threat for cultured fish worldwide, the commercialization of vaccines capable of providing effective and long-lasting protection is still lacking for most of these viral diseases. In this situation, the use of supplemented diets could be a suitable strategy to increase the immune status of the fish and reduce the impact of viral pathogens. Among possible immunostimulants that could be included in these functional feeds, some studies have previously shown that certain ß-glucans can significantly increase certain immune parameters of fish and reduce the impact of viral diseases. However, the mechanisms through which ß-glucans exert their activity have not been fully elucidated yet. In the current study, we have studied the immune response of different tissues to viral haemorrhagic septicaemia virus (VHSV) in rainbow trout fed with a non-supplemented control diet as well as in fish fed a commercial functional aquafeed (Protec™, Skretting) containing ß-glucans, vitamin C, vitamin E and zinc. For this, after 30 days of feeding the fish with one of the two diets, they were subsequently infected with VHSV by bath or mock-infected. After 2 or 6 days post-infection, fish were sacrificed and the levels of transcription of different immune genes such as IgM, IgT, IgD, Mx, interferon γ (IFN γ) and perforin studied in different tissues (kidney, gut and gills). Additionally, the levels of natural IgMs in serum were also determined. Our results demonstrate that fish fed the functional diet were capable of mounting an increased IgM, IgT, IgD and Mx transcriptional response to the virus. Additionally, these fish also showed increased levels of natural IgMs in serum. These results reveal a previously undescribed effect of functional diets on fish Ig production and point to Protec™ as an adequate diet to be incorporated in holistic programs aimed at mitigating the effect of viral diseases.

Antiviral effects of extracts from Celosia cristata and Raphanus sativus roots against viral hemorrhagic septicemia virus.

The antiviral activity of an extract mixture from Celosia cristata and Raphanus sativus was tested against viral hemorrhagic septicemia virus (VHSV). Pretreatment of EPC cells with this extract up to 72 h before VHSV infection markedly reduced the virus titer, but it had no effect when added after virus inoculation. In olive flounder that received 5 µg of extract per fish, Mx expression peaked at 48 h after treatment. In contrast, ISG15 and TLR2 expression peaked at 72 h, and that of TLR7 peaked at 48 h, followed by a slight decrease at 72 h, indicating that the antiviral activity was mediated by induction of gene expression involved in the innate immune response.