Aphanomyces invadans is the main causative agent of epizootic
ulcerative syndrome (EUS), a seasonal epizootic condition,
which is associated with morbidity and mortality in farmed and
wild fish worldwide (Roberts and others 1993, Blazer and others
1999, Baldock and others 2005, Andrew and others 2008, Boys
and others 2012, Oidtmann 2012). EUS is now considered to be
indistinguishable from mycotic granulomatosis (MG), red spot disease
(RSD), ulcerative disease syndrome (UDS) or ulcerative mycosis
(UM) (Lilley and others 1998). Approximately 76 species of
fish have been confirmed by histological diagnosis to be naturally
affected by EUS (OIE 2009). Experimental infection revealed that
European catfish (Silurus glanis) were highly susceptible to A invadans
zoospores and rainbow trout (Oncorhynchus mykiss) had moderate to
low susceptibility, whereas European eels (Anguilla anguilla) appeared
largely unaffected (Oidtmann and others 2008). Some fish such as
common carp (Cyprinus carpio), Nile tilapia (Oreochromis niloticus) and
milk fish (Chanos chanos) seem to be resistant to EUS (Lilley and others
1998). A invadans is transmitted horizontally from fish to fish
through water, where the zoospores attach to the damaged fish skin
and germinate into fungal filaments or hyphae (OIE 2009). Infected
fish demonstrate petechiae, associated with distinct dermal lesions
appearing as red spots, blackish burn-like marks or deeper ulcers with
red centres and white rims (Pathiratne and others 1994, Lilley and
Roberts 1997). The disease has been reported in Australia, countries
in Asia, the USA and Africa (FAO 2009). Recently, EUS was confirmed
in wild brown bullhead (Ameiurus nebulosus) in Lake Ontario,
Canada (OIE 2011). No reports have yet been published showing the
presence of EUS in South America (European Food Safety Authority
(EFSA) 2011).
In recent years, iridoviruses have attracted much attention due to their ecological and economic impact in various parts of the world
(Caipang and others 2004). In aquaculture, iridoviruses have been
implicated as the cause of severe disease, mortality and economic