Environmentally relevant glyphosate exposure increases susceptibility to tilapia lake virus through disruption of antiviral immunity in Nile tilapia

Fish in aquatic environments face numerous stressors, including temperature fluctuations, toxins, pollutants, and infectious pathogens, such as bacteria, viruses, water molds, fungi, and parasites. Exposure to environmental chemicals can influence the susceptibility of infectious pathogens, including tilapia lake virus (TiLV), which leads to high morbidity and mortality in both wild and farmed tilapia. This study aimed to investigate whether glyphosate exposure could increase Nile tilapia susceptibility to TiLV infection and to determine how glyphosate affects the infection process and disease development. To thoroughly assess glyphosate and TiLV as stressors, detailed analyses were conducted, including clinical sign observations, histopathological examinations, viral load measurements, and assessments of innate immune gene expression across various tissues. The key finding was that oral exposure to glyphosate at environmentally relevant sediment concentrations (1 mg/kg) for 14 days altered the expression of innate immune genes (irf3, ifn, and mx), thereby increasing tilapia susceptibility to TiLV infection. Exposure to glyphosate also worsened TiLV infection in tilapia as early as 6 days post-infection, evidenced by significantly higher viral loads, downregulation of innate immune genes (irf3, ifn, and mx), increased inflammation, and more extensive histopathological damage in critical immune and target organs. Overall, this study provides valuable insights into the environmental risk factors associated with TiLV infection and highlights the role of glyphosate as a chemical stressor that can increase fish susceptibility to this infectious disease. Finally, the findings may help in developing environmentally sustainable aquaculture practices that prioritize the health of tilapia.