Emergence of Epizootic Ulcerative Syndrome in Native Fish of the Murray-Darling River System, Australia: Hosts, Distribution and Possible Vectors

Craig A. Boys,Ian B. Marsh,Steven Hum,Les Gabor,Melinda Gabor,Stuart J. Rowland,Richard B. Callinan,Brian Gratwicke

doi:10.1371/journal.pone.0035568

Craig A. Boys, Ian B. Marsh + Show 6 more

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https://doi.org/10.1371/journal.pone.0035568

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Abstract

Epizootic ulcerative syndrome (EUS) is a fish disease of international significance and reportable to the Office International des Epizootics. In June 2010, bony herring Nematalosa erebi, golden perch Macquaria ambigua, Murray cod Maccullochella peelii and spangled perch Leiopotherapon unicolor with severe ulcers were sampled from the Murray-Darling River System (MDRS) between Bourke and Brewarrina, New South Wales Australia. Histopathology and polymerase chain reaction identified the fungus-like oomycete Aphanomyces invadans, the causative agent of EUS. Apart from one previous record in N. erebi, EUS has been recorded in the wild only from coastal drainages in Australia. This study is the first published account of A. invadans in the wild fish populations of the MDRS, and is the first confirmed record of EUS in M. ambigua, M. peelii and L. unicolor. Ulcerated carp Cyprinus carpio collected at the time of the same epizootic were not found to be infected by EUS, supporting previous accounts of resistance against the disease by this species. The lack of previous clinical evidence, the large number of new hosts (n = 3), the geographic extent (200 km) of this epizootic, the severity of ulceration and apparent high pathogenicity suggest a relatively recent invasion by A. invadans. The epizootic and associated environmental factors are documented and discussed within the context of possible vectors for its entry into the MDRS and recommendations regarding continued surveillance, research and biosecurity are made.

Highlights

The emergence and spread of aquatic freshwater diseases are a major conservation concern [1]
Aphanomyces invadans was detect as being present in N. erebi, M. ambigua, M. peelii and L. unicolor using histopathology, and the diagnosis was further confirmed in N. erebi and M. ambigua using PCR
A small number of C. carpio and C. auratus were sampled with distinct haemorrhagic, dermal lesions, histopathology and PCR (PCR performed on C. carpio only) confirmed that these were not consistent with the case definition of A. invadans [2,6,20]

Summary

Introduction

The emergence and spread of aquatic freshwater diseases are a major conservation concern [1]. One aquatic disease implicated in mass mortalities of cultured and wild fish in many countries is epizootic ulcerative syndrome (EUS) [2]. Described in cultured ayu Plecoglossus altivelis in Japan [5], within three decades EUS had been reported in more than 100 fish species [6] in both freshwater and estuarine environments throughout south, south-eastern and western Asia [7,8,9], the east coast of North America [10,11], in distinct regions of Australia: including New South Wales (NSW), Northern Territory, Queensland and Western Australia [3] and recently in Africa [12]. Referred to as Bundaberg Fish Disease, EUS was first reported in Australia in 1972 [14], and subsequently there have been numerous outbreaks reported in wild freshwater and estuarine fishes in the eastern, northern and western coastal drainages [15,16,17,18]

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