Understanding the Pathogenesis of Red Mark Syndrome in Rainbow Trout ( Oncorhynchus mykiss ) through an Integrated Morphological and Molecular Approach

• Published in: Animals (Basel) Vol. 13; no. 6; p. 1103
• Main Authors: Galeotti, Marco, Orioles, Massimo, Saccà, Elena, Byadgi, Omkar, Pesaro, Stefano, Di Cerbo, Alessandro, Magi, Gian Enrico
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.03.2023; MDPI
• Subjects: Aquaculture; Aquaculture industry; Cytokines; Deoxyribonucleic acid; Development and progression; Disease control; DNA; Epidemics; Etiology; Farms; Fishes; Freshwater aquaculture; Gene expression; Genetic testing; Health aspects; host immune response; Humoral immunity; Hyperplasia; Immune response; Immune system; Immunoglobulins; Infections; Inflammation; Interleukin 1; Interleukin 10; Interleukin 6; Lesions; Major histocompatibility complex; Midichloria-like organism; Morphology; Oncorhynchus mykiss; Organisms; Pathogenesis; Polymerase chain reaction; Quantitative PCR; Red Mark syndrome; Salmon; Scientific equipment and supplies industry; Skin; Skin diseases; Skin lesions; Spleen; Statistical analysis; Trout; Variance analysis; Water temperature; United States; Massachusetts; Germany; United States > US; Italy; host immune response; Midichloria-like organism; Oncorhynchus mykiss; Red Mark syndrome; Quantitative PCR; gene expression
• ISSN: 2076-2615; 2076-2615
• DOI: 10.3390/ani13061103

Red mark syndrome (RMS) is a widespread skin disorder of rainbow trout in freshwater aquaculture, believed to be caused by a -like organism (MLO). Here, we aimed to study the pathologic mechanisms at the origin of RMS by analyzing field samples from a recent outbreak through gene expression, MLO PCR, quantitative PCR, and a histopathological scoring system proposed for RMS lesions. Statistical analyses included a One-Way Analysis of Variance (ANOVA) with a Dunnett's multiple comparisons test to assess differences among gene expression groups and a nonparametric Spearman correlation between various categories of skin lesions and PCR results. In short, the results confirmed the presence of a high quantity of 16S gene copy numbers of -like organisms in diseased skin tissues. However, the number of -like organisms detected was not correlated to the degree of severity of skin disease. -like organism DNA was found in the spleen and head kidney. The spleen showed pathologic changes mainly of hyperplastic type, reflecting its direct involvement during infection. The most severe skin lesions were characterized by a high level of inflammatory cytokines sustaining and modulating the severe inflammatory process. IL-1 β, IL-6, IL-10, MHC-II, and TCR were upregulated in severe skin lesions, while IL-10 was highly expressed in moderate to severe ones. In the moderate form, the response was driven to produce immunoglobulins, which appeared crucial in controlling the skin disease's severity. Altogether our results illustrated a complex immune interaction between the host and -like organism.