Molecular characterization of the fish‐pathogenic fungus Aphanomyces invadans

Abstract

Aphanomyces invadans (Saprolegniaceae) is a peronosporomycete fungus associated with the serious fish disease, epizootic ulcerative syndrome (EUS), also known as mycotic granulomatosis. In this study, interspecific relationships were examined between A. invadans isolates and other aquatic animal pathogenic Saprolegniaceae, and saprophytic Saprolegniaceae from EUS-affected areas. Restriction fragment length polymorphisms and sequences of ribosomal DNA confirmed that A. invadans is distinct from all other species studied. A sequence from the internal transcribed spacer region ITS1, unique to A. invadans, was used to design primers for a PCR-based diagnostic test. Intraspecific relationships were also examined by random amplification of polymorphic DNA using 20 isolates of A. invadans from six countries. The isolates showed a high degree of genetic homogeneity using 14 random ten-mer primers. This provides evidence that the fungus has spread across Asia in one relatively rapid episode, which is consistent with reports of outbreaks of EUS. Physiological distinctions between A. invadans and other Aphanomyces species based on a data set of 16 growth parameters showed remarkable taxonomic congruence with the molecular phylogeny.

Molecular Assays for DetectingAphanomyces invadansin Ulcerative Mycotic Fish Lesions

“…The agreement between the FISH and PCR assays indicates that PCR alone could be used as a reliable diagnostic test for the presence of A. invadans infection. In addition to this assay, other A. invadans PCR assays are available (3,26,38). Blazer et al (3) used PCR to assay an unspecified number of naturally infected, formalin-preserved fish from 13 UM epidemics to demonstrate the broad geographic range of A. invadans extending from the Indian River in Delaware to a farm pond in Louisiana.…”

The Evolutionary Phylogeny of Oomycetes—Insights Gained from Studies of Holocarpic Parasites of Algae and Invertebrates

“…Aphanomyces is a genus that includes many important pathogens of crustacea (e.g., Aphanomyces astaci; Dykstra et al, 1986), fish (e.g., Aphanomyces invadans; Lilley et al, 2003), and plant roots (e.g., A. euteiches; Johnson et al, 2002), which together with several genera of little studied soil/root inhabiting oomycetes, Plectospira, Pachymetra (Reithmu¨ller et al, 1999), and Verrucalvus (Thines unpublished data) form a well-supported clade that is separate from other members of the Saprolegniaceae (Fig. 1.3).…”

Ecological diversity and economical importance of species from Aphanomyces genus

“…This phenomenon has been observed in two species of fishes from excavated earthen pond at the western shore of the Suez Canal, Egypt, during the winter of 1971 (Shaheen et al, 1999). According to Lilley et al (2003) this invasive Aphanomyces fish infection has been reported by Shaheen et al (1999) and has been caused by A. invadans species. It has also been observed on skin-muscles on aquarium species of Labeo bicolour Smith specimens and on the alevins of the Nile tilapia-Oerochromis niloticus L.…”