Dissemination, identification and treatment of Aphanomyces invadans, the causative agent of epizootic ulcerative syndrome in fish

Epizootic Ulcerative Syndrome (EUS) is an emerging infectious disease of fish caused by the oomycete Aphanomyces invadans, which belongs to the class Oomyceta and the order Saprolegniales. It was first reported in the Indo-Pacific region and has been confirmed to affect 125 fish species. Clinical signs include red spots on the skin alongside necrotizing granulomatous dermatitis and myositis in association with A. invadans hyphae. In Europe, A. invadans has been detected in ornamental fish but no clinical cases have been reported. The presence of various bacterial and viral species isolated from A. invadans-infected fish indicates their possible role as opportunistic or predisposing factors. Several diagnostic approaches to detecting the presence of A. invadans have been described, such as monoclonal antibody (MAb)-based detection, flow through immunoassay (FTA) and pyrolysis mass spectrometry (PyMS). Techniques to discriminate strains of Aphanomyces species include Random Amplification of Polymorphic DNA (RAPD), PCR Amplification of ribosomal DNA (rDNA), rDNA Sequencing, Restriction Fragment Length Polymorphism (RFLP) and Fluorescent peptide nucleic acid In-Situ Hybridization (FISH) assays. No approved chemotherapeutics or vaccines are available, so strict biosecurity measures are necessary to prevent the spread of disease and to reduce the risk of outbreaks in aquaculture facilities.