Epizootic Ulcerative Syndrome (EUS) Technical Handbook

HistoryShresta, 1994). It is estimated that 20-30% of Nepalese pond fish production(about 3000 mt) is lost every year through EUS (Pantha, unpublished report).The country to be affected most recently by EUS was Pakistan, where EUS wasconfirmed in snakeheads from Punjab Province in April 1996, and in Cirrhinusmrigal from Sindh Province in January 1998 (DFID, 1998). The blotchedsnakehead or mud murrel (Channa punctata) was the most commonly affectedspecies; with Puntius spp., Labeo rohita and Cirrhinus reba also reportedlyaffected (N. Akhthar, pers. comm.). An estimated 20% of farms were affectedin Sialkot Division, Punjab with the incidence being higher in ponds that wereinundated by flooding in 1996 (AAHRI, ACIAR, IoA and NACA, 1997). Reportedlosses have not been high in the Punjab, possibly due to the extensive use oftube-well water for fish farms and elevated salinities (AAHRI, ACIAR, IoA andNACA, 1997), but EUS is now well established in parts of the Indus river, andgiven its apparent rapid spread across the country (DFID, 1998), there arefears of potentially serious future impacts to fisheries and aquaculturedevelopment.Other similar diseasesMention is made here of other similar ulcerative fish diseases, although theirrelationship with EUS is presently unknown.Ulcerative mycosis (UM)Noga (1994) postulated that ulcerative mycosis (UM) of coastal fish populationsof the western Atlantic may be part of the same syndrome as EUS, given thesimilarities in clinico-pathological features of both diseases and thatpredominantly Aphanomyces fungi are recovered from UM-diseased fish(Dykstra et al., 1986). However, fish challenged with these Aphanomycesisolates have failed to develop lesions consistent with UM (Noga, 1993; Lilleyand Roberts, 1997). Fish have developed UM when lesion material is used asan inoculum, suggesting that some other, unidentified agent, possibly anotherfungus, is required for infection (Noga, 1993).UM was first observed in April 1984, in menhaden (Brevoortia tyrannus) in thePamlico River, North Carolina and in November of that year a massive kill wasreported (Noga and Dykstra, 1986). Epidemics of similar diseases were laterrecognised in estuaries along the eastern seaboard of USA from Connecticut(Noga, 1993) to Florida (McGarey et al., 1990), although it is uncertain whetherthese were first occurrences and represented a spread in the disease. Severalfish species were shown to contract UM-like diseases in Pamlico river (Noga etal., 1991) but the prevalence in these species was markedly lower than inmenhaden (Levine et al., 1990a). In menhaden, a larger proportion of age-0 fishwere shown to be affected than age-1 fish (Levine et al., 1990b). Levine et al.(1990b) also provided evidence that specific regions of low salinity within theTar-Pamlico estuary harboured higher levels of diseased fish, and Noga (1993)observed that the most damaging outbreaks in the Pamlico River coincidedwith years of unusually high rainfall and reduced salinity (1984 and 1989).7