Abstract
BackgroundMost of the studies on fish diseases focus on single infections, although in nature co-infections occur more often. The two freshwater myxozoan parasites of salmonids, having high economic and ecologic relevance are Tetracapsuloides bryosalmonae (Malacosporea), the etiological agent of proliferative kidney disease, and Myxobolus cerebralis (Myxosporea), the etiological agent of whirling disease. The present study aims to investigate immune modulation in rainbow trouts (Oncorhynchus mykiss) during single and co-infections by these parasites.MethodsFish were initially infected with T. bryosalmonae (one group) and M. cerebralis (another group) separately. At 30 days post-exposure (dpe), both the single species infected groups were co-infected, respectively, with the other parasite. Posterior kidney and cartilage cranium samples were collected at 30, 60, 90 and 120 dpe and RT-qPCR was performed on them to assess the transcription of suppressors of cytokine signaling (SOCS) -1 and -3, Janus kinase-1 (JAK-1) and signal transducer and activator of transcription-3 (STAT-3) genes.ResultsKidney samples from the T. bryosalmonae-infected group showed upregulation of all immune genes tested between 60–120 dpe. Crania from the single M. cerebralis-infected group and the M. cerebralis and T. bryosalmonae co-infected group exhibited upregulation of SOCS-1 and JAK-1 between 60–120 dpe and SOCS-3 at 120 dpe. However, only in the single M. cerebralis-infected group, was a statistically significant expression of STAT-3 observed at 30 and 60 dpe.ConclusionsThe results of this study indicate that both T. bryosalmonae and M. cerebralis induce overexpression of SOCS-1 and SOCS-3 genes and modulate the host immune response during the development of parasite to cause immunosuppression.
Highlights
Most of the studies on fish diseases focus on single infections, in nature co-infections occur more often
Immune gene expression in the posterior kidneys during single and co-infections Kidneys of the single Myxobolus cerebralis (Mc)-infected group displayed no significant differences in the expression of suppressors of cytokine signaling (SOCS)-1, Janus kinase-1 (JAK-1) and signal transducer and activator of transcription-3 (STAT-3) genes at all the time points, when compared to the uninfected control (F(1, 4) = 2.670, P > 0.05)
Despite the upregulation of all immune tested genes observed in this study, we found that the relative gene expressions of SOCS-1 and SOCS-3 in the posterior kidney were much higher than Janus kinase (JAK)-1 and signal transducer and activator of transcription (STAT)-3
Summary
Most of the studies on fish diseases focus on single infections, in nature co-infections occur more often. The two freshwater myxozoan parasites of salmonids, having high economic and ecologic relevance are Tetracapsuloides bryosalmonae (Malacosporea), the etiological agent of proliferative kidney disease, and Myxobolus cerebralis (Myxosporea), the etiological agent of whirling disease. Proliferative kidney disease (PKD) is caused by the myxozoan parasite, Tetracapsuloides bryosalmonae that belongs to the class Malacosprea and phylum Myxozoa [1, 2]. PKD targets the kidney and induces chronic immunopathology, granulomatous-like lesions and lymphocytic hyperplasia of the interstitial kidney tissue, along with hyperimmunoglobulinemia [7, 8]. Since this disease is temperature-dependent, climate change plays a crucial role in its pathogenesis [5]. During PKD the mortality rate can range from less than 20%, to 95–100% in serious outbreaks that are complicated by secondary infections and unfavorable farming or environmental conditions [5, 12, 13]
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