[Results]: The expression of the tight junction proteins Tjp-1 and Cldn3 was significantly lower in parasitized fish along all the intestine, while no differences were found in E-cadherin labeling. Some parasitized fish showed a significant increase in paracellular uptake measured by FITC-dextran detection in serum. Electrophysiology studies showed a decrease in transepithelial resistance in infected animals, which showed a diarrheic profile when compared to the normal absorptive profile of the control animals. Serum metabolomics revealed 3702 ions, from which the differential expression of 20 identified compounds significantly separated control from infected groups in multivariate analyses (PLS-DA), and even separated groups by intensity of infection. Of these compounds, inosine and creatine were identified as relevant and tested with commercial kits in serum samples.

[Introduction]: In animal production, enteritis is responsible for serious economic losses, being intestinal parasitism a major stress factor leading to malnutrition and lowered performance and production efficiency. The intestinal myxozoan parasite Enteromyxum leei dwells between gut epithelial cells and causes severe desquamative enteritis in gilthead sea bream (Sparus aurata) that impairs nutrient absorption causing anorexia, cachexia, growth impairment, reduced marketability and increased mortality. This study aimed to outline the gut failure produced in this fish-parasite model using a multifaceted approach and to find and validate serum non-lethal markers of gut barrier dysfunction.

[Methodology]: Intestinal integrity was studied in parasitized and non-parasitized fish by immunohistochemistry with specific markers for cellular adhesion (E-cadherin) and tight junctions (Tjp-1 and Cldn3) and by functional studies of permeability (oral administration of FITC-dextran) and electrophysiology (Ussing chambers). Serum samples from parasitized and non-parasitized fish were analyzed using non-targeted metabolomics and some significantly altered metabolites were selected to be validated using commercial kits.

[Conclusion]: This study demonstrates the loss of barrier function induced by the enteric parasite E. leei and underlines key markers to differentiate control and infected fish. The untargeted serum metabolomics approach did not reveal specific effects by the parasite, but more a profile typical of absorption dysfunction and anorexia, which are, of course, part of the disease signs.

Comunicación presentada en la 19th International Conference on Diseases of Fish and Shellfish, celebrada en Oporto (Portugal) del 9 al 12 de septiembre de 2019.

Funding: ParaFishControl H2020 project (634429), Aquaexcel2020 (652831, TNA AE10004-INTEBREAM), AGL2013-48560-R.