Prophylactic and Immunomodulatory potential of gooseberry (Phyllanthus acidus) and oregano (Coleus amboinicus) extracts against tilapia lake virus (TiLV) in tilapia.

Tilapia Lake virus (TiLV) is an emerging pathogen causing up to 90% mortality in tilapia (Oreochromis niloticus) farming. Enhancing tilapia health by modulating the non-specific immune system with herbal immunostimulants offers a promising strategy to mitigate TiLV outbreaks. This study evaluated the prophylactic efficacy of Gooseberry (Phyllanthus acidus) and Oregano (Coleus amboinicus) extracts against TiLV. Crude ethanolic extracts were prepared by Soxhlet extraction and screened for preliminary phytochemicals. The crude extracts were incorporated into the commercial pellet feed at varying concentrations (100, 300 and 500 mg/kg) to prepare the experimental diets (PA (P. acidus), CA (C. amboinicus) and PC (P. acidus + C. amboinicus)) and fed to healthy tilapia for four weeks. They were then challenged with TiLV (intra-peritoneal) to assess the prophylactic effects. The combination diet (PC) at 300 mg/kg showed the highest relative percentage survival (RPS) of 77.78%, followed by CA at 500 mg/kg. Further, fish fed a diet containing PC at 300 mg/kg showed significant (P < 0.05) improvements in haematological parameters, immune parameters, and immune gene expression (TLR-7 and IFN-β) at 24, 48, and 72 h post-infection (hpi). Notably, a significant increase in blood performance, antioxidant defence and expression of IFN-β and TLR-7 in the spleen was observed. This study emphasises the potential of herbal-based immunostimulants for developing sustainable strategies to improve fish health and resilience against TiLV.