Tenacibaculosis is an emerging disease that has become a critical concern in Chilean aquaculture. Since 2020, Tenacibaculum dicentrarchi has emerged as the second most lethal pathogen in Atlantic salmon ( Salmo salar ) farming, following Piscirickettsia salmonis . Currently, no vaccine is available against tenacibaculosis in salmonids, and control relies solely on antibiotics such as florfenicol and oxytetracycline—the same treatments used for P. salmonis outbreaks. This study aims to characterize the immune response of Atlantic salmon against T. dicentrarchi under both laboratory and field conditions.
Head kidney macrophage primary cell cultures were established from smoltified Atlantic salmon provided by Salmones Camanchaca. A Chilean isolate of T. dicentrarchi (provided by ADL Diagnostic) was cultured in FMM medium and used to stimulate cells for 24 hours at a MOI of 5. Additionally, head kidney samples were collected from Atlantic salmon showing pathological signs of T. dicentrarchi infection under field conditions. Bacterial load was quantified by qPCR, while immune responses were analyzed using qPCR, immunofluorescence, and ELISA. In vitro experiments revealed significant upregulation of inflammatory response genes, including il1b , il8 , and inos , with peak expression observed at 12h post-stimulation (Fig. 1). Immunofluorescence analysis demonstrated protein expression of TNFα and IL-10, with ELISA results confirming these findings. Under field conditions, increased gene expression of arginase , tnfa , il1b , and il12 was observed, consistent with the in vitro results. Both experimental approaches suggested a primary pro-inflammatory response mediated by the M1 macrophage profile during early stages of Atlantic salmon infection with T. dicentrarchi. This study provides a comprehensive characterization of the Atlantic salmon immune response to T. dicentrarchi infection. Acknowledgments: ANID Fondecyt Iniciación No.11240684, Salmones Camanchaca, and ADL Diagnostic.