Type I interferon-dependent response of zebrafish larvae during tilapia lake virus (TiLV) infection.

Tilapia lake virus (TiLV; genus: Tilapinevirus, family: Amnoonviridae) is a recently characterised enveloped virus with a linear, negative-sense single-stranded RNA genome, which causes high mortality in tilapia species. In the present study, we demonstrated that zebrafish (Danio rerio) larvae are susceptible to TiLV infection upon systemic injection. TiLV replicated in zebrafish larvae and caused their high mortality (of about 70%). Histopathological examination revealed that TiLV infection caused pathological abnormalities in zebrafish larvae that were well visible within the brain. Moreover, gene expression analysis revealed that TiLV infection induced up-regulation of the expression of the immune-related genes encoding pathogen recognition receptors involved in sensing of viral dsRNA (rig-I (ddx58), tlr3, tlr22), transcription factors (irf3, irf7), type I interferon (infϕ1), antiviral protein (mxa), and pro-inflammatory cytokine (il-1β). We also demonstrated the protective role of the recombinant zebrafish IFNϕ1 on the survival of zebrafish larvae during TiLV infection. Our results show the importance of type I IFN response during TiLV infection in zebrafish larvae and demonstrate that zebrafish is a good model organism to study interactions between TiLV - a newly emerging in aquaculture virus, and fish host.