No abstract

No abstract

No abstract

Piscirickettsia salmonis is the etiological agent of Piscirickettsiosis, a severe disease that affects Atlantic salmon (Salmo salar) farmed in Chile and many other areas (Norway, Scotland, Ireland, Canada and the USA). This study investigated the effects of low‐dose P. salmonis infection (1 × 102 CFU/ml) on Atlantic salmon. In this study, we challenged fish with an isolated representative of the EM‐90 genogroup via intraperitoneal injection for 42 days. Infected fish displayed decreased haematocrit and haemoglobin levels at day 13 post‐infection, indicating erythropenia, haemolysis and haemodilution. Conversely, their white blood cell counts increased on days 13 and 21 post‐infection. Additionally, their iron levels decreased from day 2 post‐infection, indicating iron deficiency and an inability to retrieve stored iron before infection. Their magnesium levels also decreased at day 28 post‐infection, possibly due to osmoregulatory problems. Also, we observed an increase in lactate dehydrogenase activity on days 5, 21, and 28 post‐infection, suggesting early symptoms of hepatotoxicity. Later analyses determined a decrease in plasma glucose levels from day 2 post‐infection. This may be attributed to the hypoxic conditions caused by P. salmonis, leading to an excess utilization of stored carbohydrates. Our results suggest that the blood parameters we studied are useful for monitoring the physiological status of Atlantic salmon infected with P. salmonis.

No abstract

Salmonid rickettsial septicemia (SRS), caused by Piscirickettsia salmonis, is one of the most devastating diseases of salmonids. However, the transcriptomic responses of Atlantic salmon (Salmon salar) in freshwater to an EM-90-like isolate have not been explored. Here, we infected Atlantic salmon parr with an EM-90-like isolate and conducted time-course qPCR analyses of pathogen load and four biomarkers (campb, hampa, il8a, tlr5a) of innate immunity on the head kidney samples. Transcript expression of three of these genes (except hampa), as well as pathogen level, peaked at 21 days post-injection (DPI). Multivariate analyses of infected individuals at 21 DPI revealed two infection phenotypes [lower (L-SRS) and higher (H-SRS) infection level]. Five fish from each group (Control, L-SRS, and H-SRS) were selected for transcriptome profiling using a 44K salmonid microarray platform. We identified 1,636 and 3,076 differentially expressed probes (DEPs) in the L-SRS and H-SRS groups compared with the control group, respectively (FDR = 1%). Gene ontology term enrichment analyses of SRS-responsive genes revealed the activation of a large number of innate (e.g. “phagocytosis”, “defense response to bacterium”, “inflammatory response”) and adaptive (e.g. “regulation of T cell activation”, “antigen processing and presentation of exogenous antigen”) immune processes, while a small number of general physiological processes (e.g. “apoptotic process”, development and metabolism relevant) was enriched. Transcriptome results were confirmed by qPCR analyses of 42 microarray-identified transcripts. Furthermore, the comparison of individuals with differing levels of infection (H-SRS vs. L-SRS) generated insights into the biological processes possibly involved in disease resistance or susceptibility. This study demonstrated a low mortality (~30%) EM-90-like infection model and broadened the current understanding of molecular pathways underlying P. salmonis-triggered responses of Atlantic salmon, identifying biomarkers that may assist to diagnose and combat this pathogen.

No abstract

Caligus rogercresseyi, a marine ectoparasite, causes notable economic losses for the Chilean salmonid industry. Nevertheless, the immunological responses of infected fish remain poorly understood, including proinflammatory cytokine generation and the respective modulatory effects of various cytokine receptors. This study evaluated mRNA expression of the NLRC5, major histocompatibility complex (MHC) class II, I-kappa-B-alpha, a regulatory that inhibits NF-kappa-B, and proinflammatory cytokines (IL-1β and IL-18) in the liver and muscle of Atlantic salmon (Salmo salar) and Coho salmon (Oncorhynchus kisutch) during a time-course C. rogercresseyi infestation trial. All assessed mRNA were strongly regulated during infestation, but S. salar showed up-regulated expression, possibly accounting for the high infestation vulnerability of this salmonid. In conclusion, this work helps to understand the modulation of the expression of different transcripts involved over short periods of C. rogercresseyi infestation in two salmonid species (S. salar and O. kisutch).