Epizootic Ulcerative Syndrome (EUS) Technical Handbook

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Epizootic Ulcerative Syndrome (EUS) Technical Handbook(Roberts et al., 1993). These isolates were shown to be capable of reproducingtypical EUS lesions when injected below the dermis of susceptible fish. All ofthese pathogenic MG, RSD and EUS isolates were shown to be slow-growingand thermo-labile in culture. Similar isolates have also been obtained fromthe Philippines, Indonesia, Bangladesh (Lilley and Roberts, 1997) and India(I. Karunasagar, pers. comm.). Recently, pathogenic Aphanomyces culturesfrom most of these countries have been compared directly, and shown bymeans of protein banding profiles (Callinan et al., 1995b; Lilley et al., 1997b),growth characteristics (Lilley and Roberts, 1997) and chemical susceptibility(Lilley and Inglis, 1997) to be all the same species. Genetic fingerprintingtechniques have also been used to show that the various isolates weregenetically all very similar (Lilley et al., 1997a). This is proof that the isolatesare not long-term residents in each locality, as would be expected ofopportunistic fungi. Instead, they are part of one fungal strain that hascolonised much of Asia and Australia in a matter of decades, and resulted inthe spread of EUS.The pathogenic Aphanomyces has been named variously as Aphanomycespiscicida (Hatai, 1980), Aphanomyces invaderis (Willoughby et al., 1995) andERA (EUS-related Aphanomyces sp.: Lumanlan-Mayo et al., 1997). As isolatesin each case have been shown to be conspecific, however, one species nameis required to describe all these isolates. As A. invadans is the only valid taxonname according to the International Code of Botanical Nomenclature (ICBN),this is the name that will be adopted here.A. invadans is known to grow fastest in culture at temperatures between 26-30 o C (Hatai and Egusa, 1978; Fraser et al., 1992; Lilley and Roberts, 1997), andhas been shown to grow in snakehead muscle tissue between 19-31 o C(Chinabut et al., 1995). However, further investigation has revealed thatsnakeheads are able to recover from A. invadans infection at highertemperatures (26, 30 o C), but are unable to prevent fungal invasion andeventually succumb to the disease at lower temperatures (19 o C) (Chinabut etal., 1995). The humoral and cellular immune response of fish are known tobe supressed at low temperatures (Avtalion et al., 1980; Bly and Clem, 1991),which may explain why mortalities from EUS occur when water temperaturesare low. Naturally and artificially infected snakeheads have been shown toproduce an antibody response against A. invadans (Thompson et al., 1997), andthe cellular macrophage response is also considered to be important inenabling fish to resist infection (Wada et al., 1996).A summary of the various published descriptions of the characteristics of A.invadans from EUS, MG and RSD outbreaks is given in Table 3. Techniquesfor isolating A. invadans from fish and water, and identifying candidatecultures to the genus Aphanomyces are given in the Annex. As with othersaprolegniacean fungi, A. invadans, is aseptate and produces two zoosporeforms, the secondary form being free-swimming and laterally biflagellate. Nosexual reproductive structures have been observed in any of the isolates fromEUS, MG or RSD outbreaks. The lack of sexual structures is considered to bea particularly common phenomenon among the more pathogenic membersof the Saprolegniaceae (Alderman and Polglase, 1988).18
AetiologyFigure 2 SporulatingAphanomyces invadansculture showing clusters ofencysted primary zoosporesfollowing discharge fromlateral evacuation tubes (fromRoberts et al. 1993)19
Page 3 and 4: Epizootic Ulcerative Syndrome(EUS)T
Page 5 and 6: Copies of this publication are avai
Page 7 and 8: This handbook is one of a series of
Page 9 and 10: ContentsIntroduction ..............
Page 11 and 12: IntroductionEpizootic ulcerative sy
Page 13 and 14: HistoryFor over 25 years, outbreaks
Page 15 and 16: HistoryAlthough there were reports
Page 17 and 18: HistoryShresta, 1994). It is estima
Page 19 and 20: Species affectedMore than 100 fish
Page 21 and 22: Species AffectedTable 1 Species sus
Page 23 and 24: Socio-economicsThe most severe impa
Page 25 and 26: Public healthPrior to the initial E
Page 27: AetiologyDiseased fish, particularl
Page 31 and 32: AetiologyInvolvement of other sapro
Page 33 and 34: Aetiologysnakehead fry died when ch
Page 35 and 36: Environmental FactorsCurrent findin
Page 37 and 38: Environmental FactorsSite character
Page 39 and 40: DiagnosisCorrect diagnosis of EUS i
Page 41 and 42: DiagnosisDiseased striped snakehead
Page 43 and 44: EpidemiologyEpidemiology is the stu
Page 45 and 46: EpidemiologyACID excessSULFATE RAIN
Page 47 and 48: Control of EUSNow that research on
Page 49 and 50: Control of EUSSurveillanceIt is imp
Page 51 and 52: Epizootic Ulcerative Syndrome (EUS)
Page 53 and 54: Epizootic Ulcerative Syndrome (EUS)
Page 55 and 56: Annex 1 - Isolation of Aphanomycesi
Page 57 and 58: Annex 2 - Count method for Aphanomy
Page 63 and 64: Annex 3 - Maintenance of Aphanomyce
Page 65 and 66: Annex 4 - Inducing sporulation inAp
Page 67 and 68: Annex 5 - Identification of saprole
Page 69 and 70: Annex 6 - Isolation of virusesThe i
Page 71 and 72: Annex 7 - Investigation of EUS outb
Page 73 and 74: Investigationof EUS outbreakspatter
Page 75 and 76: Investigationof EUS outbreaksthat s
Page 77 and 78: Annex 8 - EUS Sampling DatasheetsTo
Page 79 and 80:
EUS Sampling DatasheetsEUS SAMPLING
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Annex 9 - Procedure for samplingfis
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AbbreviationsAAHRI - Aquatic Animal
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Glossaryachlyoid:acinar necrosis:ae
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Glossarylymphoid:melanomacrophagece
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ReferencesAAHRI, ACIAR, IoA and NAC
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ReferencesCallinan, R.B., Paclibare
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ReferencesFrerichs, G.N., Millar, S
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ReferencesLilley, J.H. and Frerichs
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ReferencesNoga, E.J., Wright, J.F.,
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ReferencesRodgers, L.J. and Burke,
Page 101 and 102:
ReferencesViswanath, T.S., Mohan, C
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Epizootic Ulcerative Syndrome (EUS) Technical Handbook

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