Pathogenicity and culture studies comparing the Aphanomyces involved in epizootic ulcerative syndrome (EUS) with other similar fungi

Abstract

Pathogenicity and cultural experiments described here provide futher evidence that a distinct species of Aphanomyces is responsible for much of the characteristic pathology of epizootic ulceration syndrome (EUS). Zoospores from 58 fungal isolates were injected intramuscularly in snakehead fish, Channa striata (Bloch). These fungi comprised: Aphanomyces strains isolated from EUS‐affected fish; saprophytic Aphanomyces, Achlya and Saprolegnia spp. from infected waters; and further saprolegniaceous fungi involved in other diseases of aquatic animals. Only the Aphanomyces strains isolated from fish affected by EUS, Australian red spot disease (already considered synonymous with EUS) or mycotic granulomatosis described from Japan were able to grow invasively through the fish muscle and produce the distinctive EUS lesions. In contrast to Aphanomyces astaci Schikora, the EUS‐Aphanomyces was shown to be unable to infect noble crayfish, Astacus astacus L. The snakehead‐pathogenic strains were further distinguished from all the other fungi under comparison by their characteristic temperature‐growth profile and inability to grow on certain selective fungal media.

Characterization of Aphanomyces invadans by electrophoretic and Western blot analysis

“…Furthermore, these techniques distinguished this group of pathogens from a variety of other Oomycete fungi that have been previously shown to be nonpathogenic to EUS-susceptible fish (Lilley & Roberts 1997). The results are consistent with other studies using random amplified polymorphic DNA (RAPDs) and pyrolysis mass spectrometry (PyMS) which also indicate that the EUS, RSD and MG isolates form a homogenous group and are probably conspecific (J.…”

“…A List of the fungi used in the present study is given in Table 1 and further details can be found in Lilley & Roberts (1997).…”

“…It was described by Willoughby et al (1995) under the name Aphanomyces invaderis, but is now listed in the Index of Fungi (1997) as A. invadans. Recent work has shown that this fungus appears to be pathogenically and culturally identical to similar Aphanomyces isolates from fish suffering from redspot disease (RSD) in Australia and mycotic granulomatosis (MG) in Japan (Lilley & Roberts 1997). Strains from the latter disease, however, have been generally referred to as Aphanomyces piscicida (Hatai 1980).…”

Skin ulcers in estuarine fishes: a comparative pathological evaluation of wild and laboratory-exposed fish.

“…The causative agent is now known to be an invasive, highly pathogenic Oomycete fungus called A. invadans (14,15). This fungus is also the cause of EUS in the IndoPacific region and has caused extensive losses to commercial fisheries there since the early 1970s (11)(12)(13). However, disease outbreaks are considered a multifactorial problem because a variety of predisposing factors may be involved, the only absolute requirement being the presence of the fungus.…”

“…Outbreaks have been referred to respectively as epizootic ulcerative syndrome (EUS) in Asia, red spot disease in Australia, and mycotic granulomatosis in Japan (12). This disease has devastated several major commercial fisheries, both wild and farmed, and is now collectively referred to as EUS (13). Aphanomyces invadans, an Oomycete fungus, was recently implicated as the etiologic agent of EUS.…”