Evaluation of systemic and mucosal immune responses in Nile tilapia following intraperitoneal and immersion vaccination with inactivated tilapia lake virus (TiLV) vaccine.

Tilapia lake virus (TiLV), an orthomyxovirus, poses a significant threat to global tilapia aquaculture. However, there has been limited success in developing commercial vaccines. The current study assessed the protective efficacy of a cell culture-derived, formalin-inactivated whole virus vaccine for Nile tilapia (Oreochromis niloticus) administered via injection or immersion. Upon viral challenge, the vaccinated fish yielded relative percent survivals of 100% and 83.88% to injection and immersion vaccinations, respectively. Immune responses were assessed through standardized IgM and IgZ indirect ELISAs in blood and mucus, and through immune gene expression profiling in spleen and kidney tissues. IgM levels were significantly elevated in vaccinated fish from 14 days post-vaccination and remained detectable up to 180 days, with peak responses at days 28 (in serum) and 42 (in mucus). Similarly, IgZ level was significantly higher in vaccinated fish than in the control throughout the study period, with a peak at 28 days. Innate and adaptive immune genes (IgM, IgD, IgZ, MHC I, MHC II, CD4, IL1β, Mx, NFκβ, RSAD2, IRF3, and TLR2) were consistently up-regulated in vaccinated fish. Collectively, the results indicate that the inactivated whole-virus vaccine is capable of stimulating coordinated humoral and cellular responses against TiLV, supporting its potential use in commercial settings.