©FAO/D. Huchzermeyer, Rhodes University
How is epizootic ulcerative syndrome (EUS) diagnosed?
Figure 17. Serranochromis robustus – Nembwe. Note the deep ulcer containing white necrotic tissue in a fish affected by epizootic ulcerative syndrome (EUS), Luwombwa River, north Zambia, during 2014.
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ften the first indication of EUS is the presence of ulcerative skin lesions that are commonly found in freshwater and estuarine fishes in infected waters.
The presence of lesions often indicates a contaminated or stressed aquatic environment and may be associated with a variety of infections including parasites, bacteria, viruses and fungi, as well as non-infectious causes such as for example toxic algae. Intra-species aggression is believed to be a predisposing factor in some species such as snakehead fish. Presumptive diagnosis of EUS can be based on Level 1 diagnosis consisting of observation of gross appearance (red spots and open dermal ulcers) and Level II diagnosis using a microscope to detect aseptate branching hyphae in squashed preparations of the muscle underlying gross lesions. Confirmatory diagnosis requires: 1. histological demonstration of the typical granulomatous inflammation around invasive hyphae (Level II diagnosis) or, 2. isolation of Aphanomyces invadans from the underlying muscle (Level III diagnosis) or, 3. demonstration of genetic material belonging to A. invadans by molecular laboratory means (Level III diagnosis).
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