Enterospora nucleophila (Microsporidia) in Gilthead Sea Bream (Sparus aurata): Pathological Effects and Cellular Immune Response in Natural Infections

Abstract

<jats:p> Enterospora nucleophila is a microsporidian responsible for an emaciative disease in gilthead sea bream ( Sparus aurata). Its intranuclear development and the lack of in vitro and in vivo models hinder its research. This study investigated the associated lesions, its detection by quantitative polymerase chain reaction, and the cellular immune response of naturally infected fish. The intensity of infection in the intestine was correlated with stunted growth and reduced body condition. At the beginning of the outbreaks, infection prevalence was highest in intestine and stomach, and in subsequent months, the prevalence decreased in the intestine and increased in hematopoietic organs and stomach. In heavy infections, the intestine had histologic lesions of enterocyte hypercellularity and proliferation of rodlet cells. Infected enterocytes had E. nucleophila spores in the cytoplasm, and a pyknotic nucleus, karyorhexis or karyolysis. Lymphocytes were present at the base of the mucosa, and eosinophilic granule cells were located between the enterocytes. In intestinal submucosa, macrophage aggregates containing spores were surrounded by lymphocytes and granulocytes, with submucosal infiltration of granulocytes. Macrophage aggregates appeared to develop into granulomata with necrotic areas containing parasite remnants. Immunohistochemistry revealed mast cells as the main type of granulocyte involved. Abundant IgM<jats:sup>+</jats:sup> and IgT<jats:sup>+</jats:sup> cells were identified by in situ hybridization in the submucosa when intracytoplasmic stages were present. This study describes the lesions of E. nucleophila in gilthead sea bream, an important aquaculture species. </jats:p>

Control of enteric parasitic diseases of farmed gilthead sea bream: New insights into Enteromyxum leei (Myxozoa) and Enterospora nucleophila (Microsporidia) infections

“…Upon arrival, a subsample was sacrificed by overexposure to the anaesthetic (MS-222, 0.1 g/L; Sigma), and tested for the presence of E. nucleophila in the intestine by qPCR or by histology (see more details below). Donors for each trial were selected from these infected fish stock according to the clinical signs described previously: cachexia, swollen abdominal cavity, and thinned intestinal walls in the necropsy Picard-Sánchez et al, 2020b), and these fish were generally positive for E. nucleophila by qPCR and histology.…”

“…Healthy GSB juveniles from a commercial nursery were used as recipient fish (R), and kept in the same facilities in 5 µm-filtered and UV-treated sea water (salinity 37.5 g/L) under natural temperature and photoperiod at our latitude (40°5'N; 0°10'E). The absence of E. nucleophila in R stocks was confirmed by qPCR according to Picard- Sánchez et al (2020b). Fish were fed ad libitum a commercial diet (BioMar, Palencia, Spain) and they were kept according to the Guidelines of the European Union Council (Directive 2010/63/EU), the Spanish RD 53/2013, and the CSIC National Committee on Bioethics under approval number 2018/VSC/PEA/0240.…”

“…Enterospora nucleophila is an enteric microsporidian that affects mainly the intestine of gilthead sea bream, provoking anorexia, cachexia, and even death . Recently, a negative correlation between the intensity of E. nucleophila infections and the condition factor (CF) of infected fish has been described (Picard-Sánchez et al, 2020b), which demonstrates the growth arrestment induced by the parasite. The microsporidium is located mainly in the epithelial layer of intestinal mucosa and in the submucosa, infecting the cytoplasm of enterocytes and macrophages and the nucleus of enterocytes and rodlet cells, although other organs can be infected Picard-Sánchez et al, 2020b).…”

“…Recently, a negative correlation between the intensity of E. nucleophila infections and the condition factor (CF) of infected fish has been described (Picard-Sánchez et al, 2020b), which demonstrates the growth arrestment induced by the parasite. The microsporidium is located mainly in the epithelial layer of intestinal mucosa and in the submucosa, infecting the cytoplasm of enterocytes and macrophages and the nucleus of enterocytes and rodlet cells, although other organs can be infected Picard-Sánchez et al, 2020b). The difficulty of diagnosing this disease, due to the very minute spore size and its intranuclear location, has recently been overcome by the development of qPCR and ISH diagnostic methods, which allow detecting very low infection levels that can be considered negative by histology Picard-Sánchez et al, 2020b).…”

“…The microsporidium is located mainly in the epithelial layer of intestinal mucosa and in the submucosa, infecting the cytoplasm of enterocytes and macrophages and the nucleus of enterocytes and rodlet cells, although other organs can be infected Picard-Sánchez et al, 2020b). The difficulty of diagnosing this disease, due to the very minute spore size and its intranuclear location, has recently been overcome by the development of qPCR and ISH diagnostic methods, which allow detecting very low infection levels that can be considered negative by histology Picard-Sánchez et al, 2020b). Another impediment to study this emerging disease is the difficulty to isolate the minute spores and to obtain an in vitro culture.…”