Tilapia lake virus (TiLV) causes severe anaemia and systemic disease in tilapia

Abstract

Tilapia lake virus disease (TiLVD) is an emerging disease in tilapia that is associated with mass mortality affecting global tilapia aquaculture. In this study, red hybrid tilapias (Oreochromis spp.) were experimentally infected by intracoelomic injection with Tilapia lake virus (TiLV) to gain a better understanding of the clinicopathological changes during infection. Pale bodies and gill were observed in infected fish after 7 days of post‐challenge (dpc) associated with severe anaemia. Further haematological analysis in TiLV‐infected fish revealed decreased levels of haemoglobin and haematocrit at 3 dpc. Common pathological findings included pale and friable liver, pale intestine with catarrhal content, and dark and shrunken spleen in TiLV‐infected fish at 7 dpc and 14 dpc. Histologically, reduced numbers of red blood cells and accumulation of melano‐macrophage centre in the spleen were found in infected fish at 3 dpc, and severe lesions were more commonly observed at 7 and 14 dpc. Lymphocyte infiltration, syncytial cell formation and multifocal necrotic hepatitis were the prominent pathological findings in the liver of infected fish. The severity of pathological changes was associated with TiLV‐infection with higher viral loads and with the expression pattern of pro‐inflammatory cytokines and antiviral genes, including interferon regulatory factor 1 (irf1), interleukin (il‐8), radical s‐adenosyl methionine domain containing 2 (rsad2) and mx. Our study provides a comprehensive analysis of the haematological profile and pathological changes in tilapia during TiLV infection. Overall, lesions present in various organs, together with alteration of host immune response in TiLV‐infected fish, indicate the systemic infection of this virus. The knowledge gained from this study improves our understanding of how TiLV causes pathological and haematological changes in tilapia.

In vivo antibacterial activity of medicinal plant Sophora flavescens against Streptococcus agalactiae infection

“…GBS infection causes a systemic chronic inflammatory response in tilapia, and cytokines can regulate the inflammatory reactions (Iregui et al, 2016). In tilapia, cytokines are secreted against microbial infection (Turner et al, 2023). Balancing between anti‐ and pro‐inflammatory cytokines is important for maintaining their functions in fish.…”

Knowns and unknowns of TiLV-associated neuronal disease

“…Unlike exclusively neurotropic betanodaviruses, which have restricted replication in nervous tissue, typically the brain and retina [ 2 ] 57 , 58 ], TiLV can infect multiple organs of the host, implying that TiLV induces a systemic infection [ 48 , 59 ]. The entry receptor(s) for TiLV remain unknown.…”

“…During haematogenous spread, newly synthesized viral particles, produced at entry sites and released into the extracellular fluids, are taken up by the local lymphatic system, draining into the bloodstream (viraemia), thereby delivering virions to target organs. The systemic nature of TiLV infection [ 59 ] and the detection of TiLV antigens in circulating leukocytes [ 48 ] suggest that haematogenous spread is the main mechanism for disseminating the virus.…”

Immune responses to Tilapia lake virus infection: what we know and what we don’t know

“…In addition, a significant increase in IRF1 gene expression early during infection was observed in the liver of TiLV-infected tilapia ( 43 ). Similarly to IRF3, IRF1 is a member of the IRF family.…”