Severe pathological and transcriptional changes in haematopoietic organs of salmon suffering from salmon gill poxvirus disease.

Background: Infection with salmon gill poxvirus (SGPV) can lead to acute disease outbreaks with high mortalities caused by extensive gill pathology. In some cases, additional signs of severe red blood cell breakdown (erythrophagocytosis) are present in the spleen and kidney. This can indicate a broader systemic effect of the infection, extending beyond the gills. In a previous study, we investigated the gill histopathology and transcriptome response of salmon sampled from such an outbreak. Here, we further investigate these responses in the same fish, focusing on the haematopoietic organs.

Results: Results show that extensive accumulation of red blood cell breakdown products and phagocytosis of red blood cells were seen in the salmon suffering from salmon gill poxvirus disease. Moreover, differentially expressed genes exhibited an apparent organ-specific pattern, with a primary function involved in immune response, which was predominantly observed in the spleen and kidney. Additional antiviral responses, as well as coagulation and vascular function, apoptosis, and stress responses, were also detected in haematopoietic organs.

Conclusions: In conclusion, salmon gill poxvirus disease (SGPVD) affects haematopoietic organs, causing red blood cell breakdown and organ-specific immune responses. Gene expression patterns highlight immune activation, antiviral defence, coagulation, and stress pathways in the spleen and kidney of salmon suffering from SGPVD.