Immune Response and Protective Efficacy of Quercetin in Tilapia, <i>Oreochromis niloticus</i> Against Tilapia Parvovirus

The global tilapia farming industry is facing challenges due to tilapia parvovirus (TiPV), an emerging viral pathogen affecting cultured tilapia populations worldwide. It causes mass mortality in tilapia and high economic loss. Hence, an effective treatment is needed to control TiPV infection. Quercetin is one of the polyphenolic flavonoid compounds found in many natural products and could effectively inhibit various aquatic viral pathogens. Investigating the immunological response, virus clearance, and survival of tilapia fed quercetin-formulated feed is the primary intent of this research venture. Tilapia gill cell line (TG) exposed with quercetin up to 50 μg/mL did not show any significant morphological changes. The MTT assay was performed to assess the toxic effects of quercetin on the TG cell line. Immune-responsive genes (TNF-α, TLR-7, IL-1β, IL-8, IL-10, MHC-II, IFNγ, NF-κβ, CD4, and CD8) were studied in the head-kidney and spleen samples of fish fed with quercetin-formulated diets at different time intervals using RT-qPCR. On 10 days post-administration, all immune-related genes were significantly upregulated in the fish fed quercetin-formulated feed at a 50 mg/kg of feed. After receiving quercetin-formulated feed for 10 days post administration, the experimental fish was challenged intraperitoneally with TiPV. The viral clearance and viral load were determined by PCR and qPCR. The survival of 90% was observed in fish fed with quercetin formulated feed after TiPV challenge. Our results revealed that quercetin is an effective compound to protect tilapia from TiPV infection and also help to trigger the immune response in tilapia.