Physiological and Biochemical Characteristics of Rainbow Trout with Severe, Moderate and Asymptomatic Course of Vibrio anguillarum Infection

Abstract

This article describes the clinical manifestation of natural Vibrio anguillarum infection in rainbow trout (Oncorhynchus mykiss) during an outbreak on a fish farm. (i) Using an integrated approach, we characterized the pathogenesis of vibriosis from the morphological, hematological, and biochemical points of view. The molecular mechanisms associated with the host immune response were investigated using mass spectrometric analysis of trout plasma proteins. (ii) According to the severity of infection (the extent of tissue damage, the level of expression of pro-inflammatory genes, and changes in the leukocyte profile) three fish populations were identified among infected trout: fish with severe lesions (SL), fish with the moderate infectious process (IP) and asymptomatic fish (AS). (iii) Lymphopenia, granulocytosis, and splenomegaly were strong trends during the progression of infection and informative indicators of severe manifestation of disease, associated with hemorrhagic shock, metabolic acidosis, and massive tissue damage. (iv) As expected, pro-inflammatory interleukins, complement components, acute phase proteins, and antimicrobial peptides were implicated in the acute pathogenesis. Systemic coagulopathy was accompanied by increased antithrombotic reactions. (v) Reconstruction of metabolic pathways also revealed a high energy requirement for the immune response in severely affected fish. (vi) An unexpected result was a small difference between fish with moderate symptoms and fish with no or minor external signs of pathology (putatively resistant to infection). Increased production of antiproteases and enhanced blood coagulation cascade were observed in healthier fish, which may underlie the mechanisms of a controlled, non-self-damaging immune response to infection. (vii) Depending on the progression of the disease and the presence of the pathogen, a stepwise or linear change in the abundance of some plasma proteins was revealed. These proteins could be proposed as molecular markers for diagnosing the health and immune status of trout when cultured in fish farms.

Antibacterial Activity of Rainbow Trout Plasma: In Vitro Assays and Proteomic Analysis

“…In addition to the immunoglobulins, it was expected that complement components and acute phase proteins would be present in abundance in the fish plasma with high antimicrobial activity [1]. Indeed, the increased levels of complement components C4 and C1q (precerebellin) observed in the AP plasma were consistent with the inflammatory state of fish in the presence of foreign invaders [15,38,70]. However, the levels of other key membrane attack complex (MAC) components C1r, C3, C5, and C7, as well as certain PAMP recognition proteins (C-reactive protein, intelectin, etc.)…”

“…Plasma proteins can exert bacteriostatic effects without direct contact with pathogens by inhibiting the activity of bacterial secretions or reducing the availability of growth factors. For example, protease inhibitors such as alpha-1-antiproteinase and alpha-2-macroglobulin are known to effectively suppress bacterial digestion and dissemination [13][14][15], whereas metal-binding proteins deplete available iron, which is essential for bacterial growth [16,17].…”

SSU rRNA sequencing data for bacterial communities associated with Vibrio-infected rainbow trout (Oncorhynchus mykiss)

“…A total of 19 fish were sampled, of which 4 were asymptomatic, 9 moderately infected and 6 severely injured. The physiological state of fish specimens was estimated according to a number of parameters, documented in [3] .…”