Food and Agriculture Organization of the United Nations
What you need to know about
EPIZOOTIC ULCERATIVE SYNDROME (EUS) An extension brochure for Africa
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he designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned.
Aphanomyces sporangia, Philippine isolates,1999 ©FAO/M.B. Reantaso
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What you need to know about
EPIZOOTIC ULCERATIVE SYNDROME (EUS) An extension brochure for Africa
Food and Agriculture Organization of the United Nations Rome, 2020
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Required citation: FAO. 2020. What you need to know about epizootic ulcerative syndrome (EUS) – An extension brochure for Africa. Rome.
The designations employed and the presentation of material in this information product do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations (FAO) concerning the legal or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned. The views expressed in this information product are those of the author(s) and do not necessarily reflect the views or policies of FAO. © FAO, 2020
Some rights reserved. This work is made available under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 IGO licence (CC BY-NC-SA 3.0 IGO; https://creativecommons.org/licenses/by-nc-sa/3.0/igo/legalcode). Under the terms of this licence, this work may be copied, redistributed and adapted for non-commercial purposes, provided that the work is appropriately cited. In any use of this work, there should be no suggestion that FAO endorses any specific organization, products or services. The use of the FAO logo is not permitted. If the work is adapted, then it must be licensed under the same or equivalent Creative Commons licence. If a translation of this work is created, it must include the following disclaimer along with the required citation: “This translation was not created by the Food and Agriculture Organization of the United Nations (FAO). FAO is not responsible for the content or accuracy of this translation. The original [Language] edition shall be the authoritative edition.” Disputes arising under the licence that cannot be settled amicably will be resolved by mediation and arbitration as described in Article 8 of the licence except as otherwise provided herein. The applicable mediation rules will be the mediation rules of the World Intellectual Property Organization http://www.wipo.int/amc/en/mediation/rules and any arbitration will be conducted in accordance with the Arbitration Rules of the United Nations Commission on International Trade Law (UNCITRAL). Third-party materials. Users wishing to reuse material from this work that is attributed to a third party, such as tables, figures or images, are responsible for determining whether permission is needed for that reuse and for obtaining permission from the copyright holder. The risk of claims resulting from infringement of any third-party-owned component in the work rests solely with the user. Sales, rights and licensing. FAO information products are available on the FAO website (www.fao.org/publications) and can be purchased through publications-sales@fao.org. Requests for commercial use should be submitted via: www.fao.org/contact-us/licence-request. Queries regarding rights and licensing should be submitted to: copyright@fao.org. Cover photographs: ©FAO/D. Huchzermeyer, Rhodes University.
Preparation of this document
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his extension brochure – What you need to know about epizootic ulcerative syndrome (EUS) – provides simple facts or answers to frequently asked questions about EUS. This brochure is intended to address a wide range of audience from fish farmers and fishermen to extension officers as well as policymakers as a public information campaign to make available factual information about the disease so that awareness may be raised for better understanding of its potential impact. The original brochure, an outcome of FAO’s Technical Cooperation Project TCP/RAF/3111 Emergency Assistance to Combat Epizootic Ulcerative Syndrome in the Chobe/Zambezi River System, was prepared under the technical supervision of Dr Melba B. Reantaso (FAO) and Dr Rohana P. Subasinghe (FAO retiree). The current version of the extension brochure is focused on Africa. This was prepared by Dr Melba Reantaso and Dr David Huchzermeyer (South Africa).
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Contents Preparation of this document
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Acknowledgements vi What is epizootic ulcerative syndrome (EUS)?
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What does epizootic ulcerative syndrome (EUS) do to the fish?
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History of epizootic ulcerative syndrome (EUS) in Africa
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Location of the first recorded occurrence in Africa
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How does epizootic ulcerative syndrome (EUS) occur?
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How is epizootic ulcerative syndrome (EUS) diagnosed?
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Which species are susceptible or affected?
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Which species are not susceptible or affected by epizootic ulcerative syndrome (EUS)?
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How is epizootic ulcerative syndrome (EUS) spread? What factors cause the fish to become infected with EUS?
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Why and where is epizootic ulcerative syndrome (EUS) a problem today?
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Is it safe to eat epizootic ulcerative syndrome (EUS) fish?
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Can epizootic ulcerative syndrome (EUS)-affected fish be treated?
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Can infection be prevented?
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What can one do in the event of a disease outbreak?
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Can I collect epizootic ulcerative syndrome (EUS) samples for laboratory examination?
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References 30 Glossary 31
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Acknowledgements
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he FAO Fisheries Division (NFI) of the Food and Agriculture Organization of the United Nations (FAO), the FAO project GCP/GLO/979/NOR: “Improving Biosecurity Governance and Legal Framework for Efficient and Sustainable Aquaculture Production” funded by the Norwegian Agency for Development Cooperation and UTF/ZAM/077/ZAM: Technical Assistance to the Zambia Aquaculture Enterprise Development (ZAED): Output 4: Improving Aquatic Animal Health funded by the African Development Bank, and FAO’s Strategic Programme 5, are gratefully acknowledged for support in the preparation and compilation of this publication. Translation, printing and distribution costs were shouldered by the Southern African Development Community under the leadership of Dr Motseki Hlatshwayo. We also appreciate Prof Kishio Hatai, Dr Gilson Njunga, Dr Ben Van der Waal for providing photos.
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What is epizootic ulcerative syndrome (EUS)?
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pizootic ulcerative syndrome or EUS is the name given to a disease caused by an infection with the oomycete fungus known as Aphanomyces invadans or A. piscicida. Aphanomyces is a member of a group of organisms commonly known as water moulds; they are currently recognized asbbelonging, with diatoms and brown algae, to the group of Stramenopiles (OIE, 2019).This group of organisms contains a number of pathogens of plants and animals that have had devastating effects on agriculture and aquaculture throughout the world. In contrast to free-living saprophytic water moulds, Aphanomyces invadans is an obligate pathogen.
a
EUS is an epizootic condition affecting wild and farmed freshwater and estuarine finfish since it was first reported in 1971. In affected areas, the disease often occurs seasonally and may be worse in some years.
©FAO/B. Van der Waal, Namibia
EUS is also known by other names such as red spot disease (RSD), mycotic granulomatosis (MG), ulcerative mycosis (UM) and in 2005 it was suggested to rename EUS as epizootic granulomatous aphanomycosis (EGA) (Baldock et al. 2005). However the name EUS is most frequently used to describe the disease.
Figure 1. Enteromius paludinosus – Straightfin barb showing typical epizootic ulcerative syndrome (EUS) lesion. Caprivi Region, Namibia, 2007.
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©FAO/D. Huchzermeyer, Rhodes University ©FAO/D. Huchzermeyer, Rhodes University
Figure 2. Invading hyphae of Aphanomyces invadans (short arrows) with development of typical mycotic granulomas (long arrows) in a histological section of muscle from of an epizootic ulcerative syndrome (EUS)-affected fish (Serranochromis robustus), north Zambia, 2014 (Grocott’s methenamine stain, x40 magnification).
Figure 3. Epizootic ulcerative syndrome (EUS)-affected fish amongst small species (kasepa) harvested by fishermen and laid out onto drying racks in the sun, Bangweulu swamps, north Zambia, 2014.
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(All photos PLATE courtesy6 of AAHRI)
Histopathology of EUS-infected Thamalakane barb, Barbus thamalakanensis, collected by scoopnet on 22 May 2007 in the shallow waters of Chobe-Zambezi PLATE 1Botswana River in Kasane,
Histopathology of epizootic ulcerative syndrome (EUS)-affected Thamalakane barb, (All photos courtesy of AAHRI) Histopathology of EUS-infected dashtailonbarb Enteromius thamalakanensis, collected by scoopnet 22 May Histopathology 2007 in the shallow of EUS-infected waters of Chobe-Zambezi River in Kasane, Botswana showing typical mycotic showing typical mycotic granulomas
da
Histopathology EUS-infected da Histopathology of fungal EUS-infected the of invasive fung surrounding the invasive hyphaedashtail (whitebarbsurrounding A Histopathology ofB EUS-infected dash Histopathology of EUS-infected dashtail barb (stained showing typical mycotic showing typical mycotic granulomas Histopathology of EUS-infected das black, black arrows) in the Histopathology of EUS-infected dashtail barb arrows)Histopathology in the skin layer (H&E) Histopathology of dashtail barb barb Histopathology Histopathology of of EUS-infected dashtaildash barb EUS-infected ofEUS-infected EUS-infected dashtail showing typical mycotic gra showing typical mycotic surrounding the invasive fung surrounding the invasive fungalgranulomas hyphae (white showing typical mycotic granulomas surrounding showing typical mycotic granulomas showing typical mycoticsurroun gr showing typical mycotic granulomas (Grocott’s silver stain) showing typical mycotic gra showing typical mycotic granulomas surrounding the invasive fungal
©FAO/AAHRI
B B
©FAO/AAHRI
A A
surrounding invasive fungal hyphae the invasive fungal hyphae (white arrows) (white in the the invasive black, fungal hyphae (stained black, b (stained black arrows)fungal in the arrows) inthe the skin layer (H&E) surrounding the invasive fungal surrounding the invasive fungal hyphae (white surrounding the invasive surrounding the invasive fungal hyphae (white skin in layer (H&E) arrows) black, in the skin layer (Grocott’sin silver stai (stained black arrows) the sk arrows) the skin layer (H&E) (Grocott’s silver stain) (stained black, black arrows) inin the the ss arrows)ininthe theskin skinlayer layer(H&E) (H&E) (stained black, black arrows) arrows) (Grocott’s silver stain) (Grocott’s silver stain) (Grocott’s silver stain)
PLATE 7 21 Results Histopathology of EUS-infected dashtail barb, Barbus poechii (Steindachner, 1911), collected by scoop net on 22 May 2007 in the shallow waters of Chobe-Zambezi A A
B B
River in Kasane, 1911), collected byscoop scoop net on22 22 May 2007 theshallow shallow waters ofChobe-Zambezi Chobe-Zambezi 1911), collected net May 2007 ininthe waters of collected by by scoopnet on 22on May 2007 in the Botswana shallow waters of Chobe-Zambezi River inKasane, Kasane, Botswana River Botswana River inin Kasane, Botswana (All photos courtesy of AAHRI)
©FAO/AAHRI
©FAO/AAHRI
C D River in Kasane, Botswana PLATE 7 PLATE 7 Histopathology of EUS-infected dashtail barb, Barbus poechii (Steindachner, Histopathology of EUS-infected dashtail poechii (Steindachner, PLATE PLATE 77in theBarbus 7 barb, 1911), collected by scoop net on 22 PLATE May 2007 shallow waters of Chobe-Zambezi 1911), collected by scoop net on 22 May 2007 in the shallow waters of(Steindachner, Chobe-Zambezi Barbus poechii (Steindachner, Histopathology of EUS-infected dashtail barb, Barbus poechii Histopathology of EUS-infected dashtail barb, Histopathology of EUS-infected dashtail barb, Barbus poechii (Steindachner, 1911), River in Kasane, Botswana
ofofEUS-infected da Histopathology EUS-infected da Histopathology of EUS-infected dashtail barbbarbHistopathology Histopathology of of EUS-infected dashtail barb Histopathology of EUS-infected dashtail barb Histopathology EUS-infected dashtail Histopathology of EUS-infected das showing typical mycotic Histopathology of EUS-infected dash showing typical mycotic granulomas surrounding showing typical mycotic granulomas surround showing typical mycotic dash Histopathology of EUS-infected dashtail barb Histopathology of EUS-infected Histopathology of of EUS-infected dashtail barb showing typical typical mycotic granulomas showing mycotic granulomas Histopathology EUS-infected dashtail barb found mycotic C D CTypical mycotic granulomas D showing typical mycotic gra invasive(indicated fungaltypical hyphae (white arrows) invasive fungal hyphae (stained black, hyph black by black arrow) inpenetrating the muscle tissue of fish sample No. 1 showing typical gra surrounding invasive fungal surrounding invasive fungal hyph showing mycotic granulomas showing typical mycotic gra showing typical mycotic granulomas surrounding invasive fungal hyphae (white surrounding invasive fungal hyphae (white showing typical mycotic granulomas into the(Thamalakane muscle layer barb). (H&E) penetrating into invasive the muscle fungal layer (Grocott’s s Enteromius thamalakanensis (A) muscle tissues with mycotic granulomas (H&E); surrounding hyphae surrounding invasive fungal hyphae surrounding invasive fungal hyphae (white black, black arrows) penetrating black, black arrows) penetrating surrounding invasive fungal hyphae surrounding invasive hyphae (white arrows) penetrating into the layer (B) oomycete hyphae penetrated into theinto brainfungal ofthe the found fish; (B), (C) and (D)tissue are stained Grocott’s stain. Typical mycotic granulomas (indicated by black arrow) in the of fish sample No. surrounding invasive fungal hyphae (white arrows) penetrating muscle layer Typical mycotic granulomas (indicated by black arrow) found in muscle the muscle muscle tissue ofstain) fishwith sample No. 11 Barbus Barbus black, black arrows) penetrating black arrows) arrows) penetrating into the muscle layerblack, muscle layer (Grocott’s silverstain). stain)i black, black arrows) penetrating penetrating thamalakanensis (Thamalakane barb). (A) tissues with mycotic granulomas (H&E); (B) oomycete thamalakanensis (Thamalakane barb). (A) muscle muscle tissues with mycotic granulomas (H&E); (B)layer oomycete (Grocott’s silver arrows) penetrating into thethe muscle layer (H&E). arrows) penetrating into muscle layer muscle (H&E). muscle layer (Grocott’ssilver silverstain). stain). hyphae the stain hyphae penetrated penetrated into into the brain brain of of the the fish; fish; (B), (B), (C) (C) and and (D) (D) are are stained stained with with Grocott’s Grocott’s stain muscle layer (Grocott’s (H&E). muscle layer (Grocott’s (H&E). silver stain). (H&E). C C D D
©FAO/AAHRI
©FAO/AAHRI
©FAO/AAHRI
PLATE 2 Histopathology of epizootic ulcerative Typical Typical mycotic mycotic granulomas granulomas (indicated (indicated by by black black arrow) arrow) found found in in the the muscle muscle tissue tissue of of fish fish sample sample No. No. 11 Barbus Barbus syndrome (EUS)-affected dashtail thamalakanensis thamalakanensis (Thamalakane (Thamalakane barb). barb). (A) (A) barb, muscle muscle tissues tissues with with mycotic mycotic granulomas granulomas (H&E); (H&E); (B) (B) oomycete oomycete hyphae hyphae penetrated penetrated into into Chobe the the brain brain of of the thein fish; fish; (B), (B), (C) (C)Histopathology and and (D) (D) are are stained stained with with Grocott’s stain stain Enteromius poechii. River Kasane, of Grocott’s EUS-infected dashtail barb Histopathology of EUS-infected dashtail barb typical mycotic granulomas showing Botswana, typical2007.mycotic granulomas showing Histopathology EUS-infected dashtail barb Histopathology of fungal EUS-infected the of invasive fungal hyphae surrounding the invasive hyphaedashtail (whitebarbsurrounding Histopathology of EUS-infected dashtail barb Histopathology of EUS-infected dashtail barb (stained showing typical mycotic granulomas showing typical mycotic granulomas Histopathology of EUS-infected dashtail barb black, black arrows) in the skin layer Histopathology of EUS-infected dashtail barb arrows)Histopathology in the skin layer (H&E) Histopathology of EUS-infected dashtail barb Histopathology of EUS-infected dashtail barb Dashtail barb, Barbus poechii (Steindachner, (Steindachner, 1911),exhibiting exhibiting haemorrhagicderm der Histopathology of EUS-infected dashtail barb of EUS-infected dashtail barb showing typical mycotic granulomas showing typical mycotic granulomas Dashtail barb, Barbus poechii 1911), haemorrhagic surrounding the invasive fungal hyphae surrounding the invasive fungalbarb, hyphae (white showing typical mycotic granulomas surrounding showing typical mycotic granulomas surrounding showing typical mycotic granulomas showing typical mycotic granulomas (Grocott’s silver stain) showing typical mycotic granulomas Dashtail barb, Enteromius poechii, exhibiting Dashtail Barbus poechii (Steindachner, 1911), exhibiting haemorrhagic derma showing typical mycotic granulomas Dashtail barb, Barbus poechii (Steindachner, 1911), exhibiting haemorrhagic derma Dashtail barb, Barbus poechii (Steindachner, 1911), exhibiting haemorrhagic der Dashtail barb, Barbus poechii (Steindachner, 1911), posterior to anus and towards the caudal peduncle. surrounding the invasive fungal hyphae surrounding the invasive fungal hyphae (white the invasive fungal hyphae (white arrows) in the posterior the invasive fungal hyphae (stained black, black tohaemorrhagic anus and towards the caudal peduncle. (stained black, black arrows) in the skin layer arrows) in the skin layerfungal (H&E) surrounding the invasive hyphae surrounding the invasive fungal hyphae(white (white haemorrhagic dermatitis posterior tofungal anus and surrounding the invasive fungal hyphae exhibiting dermatitis posterior to surrounding the invasive hyphae posterior toanus anus and towards the caudal peduncle. skin in layer (H&E) posterior toanus and towards caudal peduncle. arrows) in the skin layer (Grocott’s silver stain) (stained black, black arrows) in the skin layer posterior to and towards the caudal peduncle. arrows) the skin layer (H&E) (Grocott’s silver stain) (stained black, black arrows) in the skin layer arrows) in the skin layer (H&E) towards the caudal peduncle. anus and towards the caudal peduncle (stained black, black arrows) in the skin layer arrows) in the skin layer (H&E) (Grocott’s silver stain) (Grocott’s silver stain) (Grocott’s silver stain)
ofofEUS-infected dashtail barb Histopathology EUS-infected dashtail barb Histopathology of EUS-infected dashtail barbbarbHistopathology Histopathology ofof EUS-infected dashtail barb Histopathology ofofEUS-infected dashtail barb Histopathology of EUS-infected dashtail Histopathology epizootic ulcerative syndrome Histopathology epizootic ulcerative syndromebarb Histopathology of EUS-infected dashtail showing typical mycotic granulomas Histopathology of EUS-infected dashtail barb showing typical granulomas surrounding showing typical mycotic granulomas surrounding showing typical mycotic granulomas Histopathology of EUS-infected dashtail barb Histopathology of EUS-infected dashtail barb Histopathology ofmycotic EUS-infected dashtail barb showing typical mycotic granulomas (EUS)-affected dashtail barb showing typical (EUS)-affected dashtail barb showing typical showing typical mycotic granulomas Histopathology of EUS-infected dashtail barb showing typical mycotic granulomas invasive fungaltypical hyphae (white arrows) penetrating invasive fungal hyphae (stained black, hyphae black arrows) showing typical mycotic granulomas surrounding invasive fungal (stained surrounding invasive fungal hyphae (stained showing mycotic granulomas showing typical mycotic granulomas mycotic granulomas surrounding invasive fungal mycotic granulomas surrounding invasive fungal showing typical mycotic granulomas surrounding invasive fungal hyphae (white surrounding invasive fungal hyphae (white showing typical mycotic granulomas penetrating into the muscle layer (H&E) into invasive the muscle fungal layer (Grocott’s surrounding hyphaesilver (stained surrounding invasive fungal hyphae (stained surrounding invasive fungal hyphae (white black,black black arrows) penetrating into black, arrows) penetrating into the the surrounding invasive fungal hyphae (stained hyphae (white arrow) penetrating into the muscle hyphae (stained black, black arrow) penetrating surrounding invasive hyphae (white stain) arrows) penetrating into thehyphae muscle layer surrounding invasive fungal (white arrows) penetrating intofungal the muscle layer black, black arrows) penetrating into the black, black arrows) penetrating into the arrows) penetrating into the muscle layer muscle layer (Grocott’s silver stain). layer (H&E). into the muscle layer (Grocott´s silver stain). black, black arrows) penetrating into the muscle layer (Grocott’s silver stain). arrows) penetrating into the muscle layer (H&E). penetrating into the muscle layer muscle layer (Grocott’s silver stain). (H&E).arrows) muscle layer (Grocott’s silver stain). (H&E). (H&E). (H&E).
muscle layer (Grocott’s silver stain).
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What does epizootic ulcerative syndrome (EUS) do to the fish? Clinical signs of EUS in affected fish showing the range of lesions
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©FAO/D. Huchzermeyer, Rhodes University
US causes unsightly lesions in affected fish. EUS-affected fish may swim slowly, show abnormal swimming movements, and in rivers may be observed near the riverbanks swimming with the current where healthy fish swim against the current. Sick fish will also seek out shallow vegetated areas of still waters.
©FAO/D. Huchzermeyer, Rhodes University
Figure 5. Labeo lunatus – upper Zambezi labeo with early lesion of epizootic ulcerative syndrome (EUS). Note red appearance of the lesions and swelling of the surrounding tissue, Chobe River, Botswana, 2007 (Andrew et al., 2008).
Figure 6. Clarias gariepinus – Sharptooth catfish affected by epizootic ulcerative syndrome (EUS) showing both the red spots that are typical of early infection and the large, deep ulcers that develop later. Fish sampled during an EUS outbreak, Bangweulu swamps, north Zambia, 2014.
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Lesions can range from small pinpoint red spots, haemorrhagic spots, localized swelling and localized raised areas on the body surface with protruding scales or scale loss to skin erosion, exposure of underlying musculature and extensive ulceration. Ulcers or ‘wounds’ can be found over a broad area of the body with the center of the lesions containing dead tissue.
©FAO/R. Bills, South African Institute of Aquatic Biodiversity
Lesions are observed most often on the lateral surface but can also occur on any part of the body.
©FAO/D. Huchzermeyer, Rhodes University
Figure 7. Enteromius poechii – Dashtail barb with typical early lesion of epizootic ulcerative syndrome (EUS), Kabompo River, upper Zambezi, 2010 (Huchzermeyer and Van der Waal, 2012).
Figure 8. Marcusenius macrolepidotus – Northern bulldog. Note the unilateral ulcerating lesion typical of epizootic ulcerative syndrome (EUS) at the base of the pectoral fin, Equateur Province, Democratic Republic of Congo (DRC), 2015.
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©FAO/O. Weyl South African Institute of Aquatic Biodiversity ©FAO/B. Van der Waal, Namibia
Figure 9. Hydrocynus vittatus – Tigerfish. Extensive dermal ulceration typical of epizootic ulcerative syndrome (EUS), Okavango River, 2010 (Huchzermeyer and Van der Waal, 2012).
©FAO/B. Van der Waal, Namibia
Figure 10. Brycinus lateralis - silver robber with early lesions typical of epizootic ulcerative syndrome (EUS) possibly associated with preceding predator injury to the skin, Kafue River, Zambia, 2007.
©FAO/D. Huchzermeyer, Rhodes University
Figure 11. Serranochromis macrocephalus - purpleface largemouth with an advanced lesion typical of epizootic ulcerative syndrome (EUS) showing extensive ulceration, fish farm, Caprivi, Namibia, 2008.
Figure 12. Parachanna obscura – Snakehead. Note ulcerating lesions typical of epizootic ulcerative syndrome (EUS) in the tail region of a fish sampled, Equateur Province, Democratic Republic of Congo (DRC), 2015.
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History of epizootic ulcerative syndrome (EUS) in Africa
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ollowing on reports of large numbers of fish with ulcers in the Chobe River on the border between Botswana and Namibia in 2006 (Figure 13), surveys initiated in February 2007 revealed the condition to be present in fish in the Chobe River in the vicinity of the Chobe Game Reserve in Botswana, the Caprivi Region of Namibia and on the Zambian side of the Zambezi River above Victoria Falls.The disease was subsequently confirmed as the first outbreak of EUS on the African continent. In this area, EUS-infected fish have been observed seasonally at the end of subsequent summers, but with a lower prevalence. Reports from Zambia have indicated a rapid spread upstream in the Zambezi River and some of its tributaries, in some cases associated with large-scale fish mortality, as well as in the Kafue River. In 2010, outbreaks of EUS in fish were reported from the Okavango Delta in Botswana, and in 2011, from Lake Liambezi in Namibia. Three outbreaks of EUS were reported from Western Cape Province of South Africa in 2011 and 2012. The disease was first noticed affecting a number of fish species in an artificial impoundment on the Palmiet River, and in a farm dam on the Eerste River. A further outbreak in the Limpopo catchment in the North West Province of South Africa was reported in 2014. Other cases were reported from estuarine fish in the Western Cape Province in 2015, and in 2016 from a river in the Western Cape Province and from an impoundment in the Northern Cape Province. A single case was reported from the Kruger National Park in Limpopo Province in 2017. The first occurrence of EUS in the headwaters of the Congo River was reported from the Bangweulu Wetlands in the north of Zambia in 2014, where in subsequent years, the disease reappeared annually at the end of the rainy season. The first outbreak of EUS in the Democratic Republic of Congo, affecting the Equateur Province in the north west of that country, was confirmed and reported in 2015. Zimbabwe reported two outbreaks of EUS for the first time in 2016 from Mashonaland East and Midlands Provinces with further outbreaks reported subsequently. Reports of EUS from Malawi were made for the first time in July 2020 from the Bua River in the Central Province. Following no reports of disease from Botswana since 2010, an outbreak of EUS associated with high mortality was again reported from the Chobe River in July 2020. In Southern Africa, EUS has had its greatest impact on floodplains, and flood plain fisheries have been particularly hard hit. The annual flooding cycle in the floodplains of the Zambezi system and elsewhere creates conditions particularly favourable to outbreaks of EUS.
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Location of the first recorded occurrence in Africa
Map conforms to United Nations Map No. 4170 Rev. 18.1 UNITED NATIONS February 2020.
©FAO/C. Huchzermeyer, Bangweulu Wetlands, African Parks
Figure 13. First recorded occurrence of epizootic ulcerative syndrome (EUS) in the Chobe River on the border between Botswana and Namibia, 2006.
Figure 14. Climbing perch, Ctenopoma multispine, a species frequently affected by epizootic ulcerative syndrome (EUS) during the annual outbreaks of epizootic ulcerative syndrome (EUS) that have occurred in the Bangweulu swamps, north Zambia, since 2014 (Huchzermeyer et al., 2018).
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How does epizootic ulcerative syndrome (EUS) occur?
S
easonal climatic conditions can create environments that favour occurrence of EUS. In many parts of Africa, for instance, the drop in temperature at the end of the rainy season, seasonal draining of floodplains during the winter months and flood-drought cycles that favour acidification of surface waters have been associated with outbreaks of EUS. Infection in fish leading to EUS occurs when motile spores (zoospores) of A. invadans are released into the water from infected fish or other carriers/vectors. The zoospores are attracted to the skin of the fish. ©FAO/K. Hatai and FAO Fisheries Technical Paper 402/2
The spores penetrate compromised areas of skin and germinate, forming fungal filaments or hyphae. The hyphae invade widely into the surrounding skin and deeply into the underlying muscle, resulting in extensive destruction of tissues leading to ulceration. The hyphae will produce sporangia that eventually release further motile spores. The sporangia are narrow, with diameters similar to that of the hyphae.
Figure 15. Typical characteristic of Aphanomyces sporangium (Japanese isolate).
©S. Kanchanakhan (June 2007)
A single row of primary zoospores formed within a zoosporangium are then released through the sporangium to encyst at the apical tip of the sporangium to form achlyoid clusters. From here, the main freeswimming stage of Aphanomyces spp., the secondary zoospore, is discharged into the water to seek out a further fish to infect.
Figure 16. Sporulation of the Botswana oomycete isolate successfully identified as Aphanomyces by the Aquatic Animal Health Research Institute (AAHRI), Thailand, June 2007.
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©FAO/D. Huchzermeyer, Rhodes University
How is epizootic ulcerative syndrome (EUS) diagnosed?
Figure 17. Serranochromis robustus – Nembwe. Note the deep ulcer containing white necrotic tissue in a fish affected by epizootic ulcerative syndrome (EUS), Luwombwa River, north Zambia, during 2014.
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ften the first indication of EUS is the presence of ulcerative skin lesions that are commonly found in freshwater and estuarine fishes in infected waters.
The presence of lesions often indicates a contaminated or stressed aquatic environment and may be associated with a variety of infections including parasites, bacteria, viruses and fungi, as well as non-infectious causes such as for example toxic algae. Intra-species aggression is believed to be a predisposing factor in some species such as snakehead fish. Presumptive diagnosis of EUS can be based on Level 1 diagnosis consisting of observation of gross appearance (red spots and open dermal ulcers) and Level II diagnosis using a microscope to detect aseptate branching hyphae in squashed preparations of the muscle underlying gross lesions. Confirmatory diagnosis requires: 1. histological demonstration of the typical granulomatous inflammation around invasive hyphae (Level II diagnosis) or, 2. isolation of Aphanomyces invadans from the underlying muscle (Level III diagnosis) or, 3. demonstration of genetic material belonging to A. invadans by molecular laboratory means (Level III diagnosis).
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©FAO/D. Huchzermeyer, Rhodes University
©FAO/D. Huchzermeyer, Rhodes University
Figure 19. Appearance of hyphae of Aphanomyces invadans in a histological section of muscle stained with Grocott’s methenamine stain (x400 magnification). Note that the walls of the hyphae stain almost black and are surrounded by a sheath of macrophages (arrows) within necrotic muscle tissue. The sample was collected from Labeo lunatus during the 2007 outbreak of epizootic ulcerative syndrome (EUS), Chobe River, Botswana.
©FAO/R. Bills, South African Institute of Aquatic Biodiversity
Figure 18. Appearance of hyphae of Aphanomyces invadans within sheaths of macrophages within an area of necrotic muscle in a histological section stained with haematoxylin and eosin (x400 magnification). The sample was collected from a Labeo lunatus suffering from epizootic ulcerative syndrome (EUS), Botswana, 2007 outbreak period. Long arrows point to hyphae in longitudinal section, short arrows point to hyphae in cross section.
©G. Njunga
Figure 20. Hepsetus odoe – African pike. Note the ulcerative lesion typical of epizootic ulcerative syndrome (EUS) near the anal fin, Kabompo River, upper Zambezi, 2010.
Figure 21. Enteromius paludinosus with epizootic ulcerative syndrome (EUS) lesions, Kasungu Water Board reservoir dam, Malawi, 2020.
11
Which species are susceptible or affected?
M
©FAO/D. Huchzermeyer, Rhodes University
ore than 160 species, worldwide, are susceptible to EUS, including farmed, wild, freshwater and estuarine fish. Many of these have been reported from the Zambezi floodplains.
©FAO/R. Peel, Department of Ichthyology and fisheries Science, Rhodes University
Figure 22. Clarias gariepinus – Sharptooth catfish with multiple deep ulcers caused by infection with Aphanomyces invadans, from the Bangweulu swamps, north Zambia, 2014.
Figure 23. Serranochromis robustus – Nembwe with a deep ulceration typical of epizootic ulcerative syndrome (EUS), below Popa Falls, Okavango River, Nambia, July 2010 (Huchzermeyer and Van der Waal, 2012).
12
Table 1. Fish species from which infection with Aphanomyces invadans has been reported in Southern and Central Africa (updated from FAO, 2009) Scientific name
Common name
Sources: Country with confirmed diagnosis (year)
Brycinus lateralis
Striped robber
Namibia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Caffrogobius nudiceps
Barehead goby
South Africa (2015)
Clarias sp.
Catfish
Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Clarias gariepinus
Sharptooth catfish
Namibia (2007) – FAO (2009) Zambia (2008) – FAO (2009) Caprivi, Zambezi (2007)* South Africa (2011) Zimbabwe (2018) Botswana (2020)
Clarias ngamensis
Blunttooth catfish
Namibia (2007) – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)* Zimbabwe (2018) Botswana (2020)
Clarias theodorae
Snake catfish
Democratic Republic of Congo (2015) – FAO (2017)
Coptodon rendalli
Redbreast tilapia
Namibia (2008) – FAO (2009) Caprivi, Zambezi (2007)*, Zimbabwe (2016) Botswana (2020)
Ctenopoma multispine
Climbing perch
Zambia (2014)
Enteromius haasianus
Sickle-fin barb
Namibia (2014)
Enteromius paludinosus
Straightfin barb
Namibia (2007) – FAO (2009) Caprivi, Zambezi (2007)*, Zambia (2014), Zimbabwe (2016) Zimbabwe (2018)
Enteromius poechii
Dashtail barb
Botswana (2007) – FAO (2009) Namibia (2007) – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)* Zimbabwe (2018)
Enteromius thamalakanensis
Thamalakane barb
Botswana (2007) – FAO (2009)
Enteromius trimaculatus
Threespot barb
Zambia (2014)
Enteromius unitaeniatus
Longbeard barb/slender barb
Namibia (2008) – FAO (2009) Caprivi, Zambezi (2007)* Namibia (2014)
Hepsetus odoe
African pike
Namibia (2007) – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)* Botswana (2010)
Hydrocynus vittatus
Tigerfish
Namibia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Labeo capensis
Orange River mudfish
South Africa (2016)
Labeo cylindricus
Redeye labeo
Namibia (2008) – FAO (2009) Caprivi, Zambezi (2007)*
Labeo lunatus
Upper Zambezi labeo
Botswana (2007) – FAO (2009) Namibia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Lepomis macrochirus
Bluegill sunfish
South Africa (2011)
Marcusenius macrolepidotus
Northern bulldog
Namibia (2007) – FAO (2009) Caprivi, Zambesi (2007)*
Micralestes acutidens
Sharptooth tetra/silver robber
Namibia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
13
Table 1. (Continued) Scientific name
Common name
Micropterus salmoides
Largemouth bass
South Africa (2011) Zimbabwe (2018)
Micropterus dolomieu
Smallmouth bass
South Africa (2016)
Mormyrus lacerda
Western bottlenose
Onchorhynchus mykiss
Rainbow trout
South Africa (2011)
Oreochromis andersonii
Threespot tilapia
Namibia (2007) – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)* Zimbabwe (2018)
Oreochromis macrochir
Greenhead tilapia
Namibia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Oreochromis mossambicus
Mozambique tilapia
Zimbabwe (2016)
Oreochromis shiranus
Shire tilapia
Malawi (2020)
Parachana obscura
Snakehead
Democratic Republic of Congo (2015) – FAO (2017)
Petrocephalus catostoma
Northern Churchill
Botswana (2008) – FAO (2009) Caprivi, Zambezi (2007)* Democratic Republic of Congo (2015) – FAO (2017)
Pharyngochromis acuticeps
Zambezi happy/Zambezi river bream
Namibia (2008), suspected – FAO (2009) Caprivi, Zambezi (2007)*, Zambia (2007-2008)
Pollimyrus isidori
Elephantfish
Zambia (2014)
Protopterus annectens
Lungfish
Democratic Republic of Congo (2015) – (2017)
Sargochromis carlottae
Rainbow bream/happy
Namibia (2008) – FAO (2009)
Sargochromis codringtonii
Green bream
Namibia (2008) – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Sargochromis giardi
Pink bream
Namibia (2008) – FAO (2009) Caprivi, Zambezi (2007)*
Schilbe intermedius
Silver catfish/butter barbel
Namibia (2007) – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)* Botswana (2010)
Serranochromis angusticeps
Thinface largemouth
Namibia (2008), suspected – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)*
Serranochromis macrocephalus
Purpleface largemouth
Namibia (2008), suspected – FAO (2009) Caprivi, Zambezi (2007)*
Serranochromis robustus
Nembwe/Tsungwa
Namibia (2007), suspected – FAO (2009) Zambia (2007) – FAO (2009) Caprivi, Zambezi (2007)* Zimbabwe (2018)
Synodontis sp.
Squeaker
Democratic Republic of Congo (2015) – FAO (2017) Botswana (2020)
Tilapia ruweti
Okavango tilapia
Tilapia sparmanii
Banded tilapia
* Caprivi, Zambezi (2007) from Huchzermeyer and Van der Waal (2012).
14
Sources: Country with confirmed diagnosis (year)
Namibia (2008) – FAO (2009) Caprivi, Zambezi (2007)* Botswana (2020)
©G. Njunga
©FAO/D. Huchzermeyer, Rhodes University
Figure 24. Clarias gariepinus, Enteromius paludinosus and Petrocephalus catostoma with multiple lesions of epizootic ulcerative syndrome (EUS), Bua River, Mchinji District, Malawi, July 2020.
©FAO/D. Huchzermeyer, Rhodes University
Figure 25. Parachanna obscura – Snakehead. Note deeply ulcerating lesions associated with epizootic ulcerative syndrome (EUS) extending into the bony structures of the head, Equateur Province, Democratic Republic of Congo (DRC), 2015.
Figure 26. Enteromius paludinosus – Straightfin barb with an early lesion typical of epizootic ulcerative syndrome (EUS), Bangweulu swamps, north Zambia, 2014.
15
©FAO/C. Huchzermeyer, Bangweulu Wetlands, African Parks ©G. Njunga
©G. Njunga
Figure 27. Clarias gariepinus – Sharptooth catfish. Note the deeply ulcerative lesion exposing underlying dead muscle tissue typical of epizootic ulcerative syndrome (EUS), Bangweulu swamps, north Zambia, 2014.
16
Figure 28. Clarias gariepinus with lesions of epizootic ulcerative syndrome (EUS), Lusa River, Mchinji District, Malawi, July 2020.
Figure 29. Clarias gariepinus with lesions of epizootic ulcerative syndrome (EUS), Lusa River, Mchinji District, Malawi, July 2020.
Which species are not susceptible or affected by EUS?
N
ile tilapia (Oreochromis niloticus), common carp (Cyprinus carpio) and milk fish (Chanos chanos) are believed to be naturally resistant to infection with Aphanomyces invadans.
©FAO/D. Huchzermeyer, Rhodes University
Nile tilapia and common carp are frequently farmed species in Africa and feral populations are widespread in some natural waters.
©FAO/T. Sinclair, Lydenburg, South Africa
Figure 30. Oreochromis niloticus – Nile tilapia. Farmed fish such as this one from a farm on Lake Kariba, Zimbabwe, have been extensively introduced for aquaculture in Zambia and Zimbabwe.
Figure 31. Cyprinus carpio – Common carp. An introduced species that has become feral in some freshwater systems in Southern and Central Africa and is popular with recreational fishermen.
17
How is epizootic ulcerative syndrome (EUS) spread? What factors cause the fish to become infected with EUS?
S
uccessful invasion and establishment of EUS in fish requires epithelial tissue damage, a susceptible fish species and environmental conditions which favour sporulation of A. invadans. In some countries, outbreaks occur in wild fish first and then spread into fish ponds. A number of risk factors are associated with EUS occurrence; some are predisposing factors, others are environmental conditions and biological factors that contribute to the occurrence of EUS. Shipping movements, ballast water, fish migrations and ocean currents are potential pathways by which the pathogen can spread between water bodies. Cross border movement of fish for aquaculture and the ornamental fish trade are proven pathways by which the disease spreads. Some EUS outbreaks follow heavy rainfall and flood events; reductions in water temperature, alkalinity and salinity; and acidified run-off water from acid sulphate soil areas have been associated with outbreaks of disease.
©FAO/D. Huchzermeyer, Rhodes University
Parasites and rhabdoviruses have also been associated with particular outbreaks, and secondary gram-negative bacteria invariably infect EUS lesions.
Figure 32. Fishing nets may be infected with spores of Aphanomyces invadans and should be dried immediately after use, and not be left where they remain wet as in this picture, Bangweulu swamps, north Zambia, 2014 outbreak of epizootic ulcerative syndrome (EUS).
18
©FAO/D. Huchzermeyer, Rhodes University ©D. K. Hatai ©D. K. Hatai
©D. K. Hatai
Figure 33. The ornamental variety of the common carp (koi) is a popular and often valuable fish that is imported into many countries for ornamental purposes. Some varieties of koi have been shown to be susceptible to epizootic ulcerative syndrome (EUS).
Gold carassius is theand susceptibility Aphanomyces Figure 34.fish, GoldCarassius fish, Carassius auratus,auratus is a popular widely tradedtoornamental fish that is known to be susceptible to epizootic ulcerative syndrome (EUS). piscicida. (Hatai, 1980) Gold fish, Carassius carassius auratus is the susceptibility to Aphanomyces
piscicida. (Hatai, 1980) auratus is the susceptibility to Aphanomyces Gold fish, Carassius carassius piscicida. (Hatai, 1980)
19
©FAO/D. K. Hatai
©FAO/D. K. Hatai
Figure 35. Aphanomyces invadans infection in dwarf gourami, another popular ornamental fish species susceptible to epizootic ulcerative syndrome (EUS), (K. Hatai et al., 1994).
©FAO/D. K. Hatai ©FAO/D. K. Hatai
©FAO/D. K. Hatai
©FAO/D. K. Hatai
Aphanomyces invadans infection in dwarf gourami (Hatai et 1994) al., 1994) Aphanomyces invadans infection in dwarf gourami (Hatai et al.,
Figure 36. Hyphae in muscle squash preprations of lesions of ayu Plecoglossus altivelis with mycotic granulomatosis (Arrow: granuloma).
20
Why and where is epizootic ulcerative syndrome (EUS) a problem today?
E
US is one of the most serious aquatic diseases known to affect finfish.
The disease causes high losses to fish farmers and fishermen through mortalities and reduced productivity of all susceptible fish species. Market rejection and public health concerns due to the presence of unsightly lesions provide for further losses. EUS has been reported from at least 28 countries and from four continents (North America, Africa, Asia and Australia). More than 160 species of finfish are susceptible to EUS. Almost a third of these occur in Southern and Central Africa. Other indirect long-term effects include the threat to the environment and aquatic biodiversity through, for example, declining fish numbers and irreversible ecological damage. EUS has the potential to financially decimate those who rely on fishing for income. In addition, and perhaps more importantly, EUS outbreaks threaten food security for subsistence fishers and fish farmers and consequently people’s physical health, as fish forms an important source of animal protein for people in many affected countries. The spread of EUS across Asia from Japan and Australia where it was first identified in the early 1970s to Pakistan in 1996 and to southern Africa in 2006 is a major epizootiological phenomenon. EUS is an OIE-listed disease, and notification to the World Organization for Animal Health (or OIE) is required in the event of an outbreak.
21
Map showing the current global distribution of epizootic ulcerative syndrome (1971 to 2020)
150
Figure 37. Chronology of global occurrence of EUS; dates with question mark indicate outbreaks of ulcerative fish disease and/or unconfirmed EUS outbreaks; dates without question mark indicate year of EUS confirmation (Lilley et al., 1998; Baldock et al., 2005; FAO, 2009). Japan (1971); Australia (Queensland – 1972, New South Wales – 1989, Northern Territory – 1990 and Western Australia – 1994); Papua New Guinea (1975 –1976?; 1982–1983?; 1986); Indonesia (1980?; 1993–1994); Singapore (1977?); Malaysia (1979?; 1980); Thailand (1981); Myanmar, Lao People’s Democratic Republic and
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Cambodia (1983 or 1984); Viet Nam (1983?); China (1982?; 1987–1988?; 1989?); China, Hong Kong SAR (1988?); Philippines (1985); Sri Lanka (1987); Bangladesh (1988); India (1988); Bhutan and Nepal (1989); Pakistan (1996); United States of America (North Carolina, Florida and Connecticut – 1984); Botswana (2006?; 2007; 2010; 2020); Namibia (2006?; 2007); Zambia (2007?; 2008; 2014); Canada (2010); Zimbabwe (2016); South Africa (2011; 2014; 2015; 2016; 2017); Democratic Republic of Congo (2015); Malawi (2020).
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LAO PEOPLE'S MYANMAR DEM. REP.
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23
Is it safe to eat epizootic ulcerative syndrome (EUS) fish?
T
he agent causing EUS does not pose any direct human health risk.
The deep ulcerations and tissue decay in fish infected with EUS may harbour secondary pathogens which may have health implications to humans consuming such fish.
©FAO/D. Huchzermeyer, Rhodes University
Thorough cooking may destroy pathogens, such as A. invadans. However, fish tissues compromised by EUS may spoil rapidly and render a product of inferior nutritional value. It is therefore advisable to avoid eating fish showing gross lesions of EUS.
Figure 38. It is believed that traditional methods such as smoking used to preserve fish products, as in the case of these fish in the Democratic Republic of Congo (DRC) in 2015, will destroy the agent of epizootic ulcerative syndrome (EUS).
24
Can epizootic ulcerative syndrome (EUS)-affected fish be treated?
T
here is no known treatment by which EUS-affected fish can be treated. Control of EUS in natural waters (e.g. rivers) is impossible.
Fish farmers whose farmed fish have been affected with EUS are encouraged to culture, where possible, non-EUS susceptible species or avoid farming susceptible species during the season when EUS is prevalent, i.e. high rainfall period and low temperature season. A strict ban on the movement of fish from infected waterways or river systems, especially those with lesions of EUS, to other waterways or river systems is recommended; diseased fish should not be moved from one fish farm to another. Particular care should be taken when moving resistant species, such as Nile tilapia, from hatcheries situated on potentially infected waters. Fish species susceptible to EUS may inhabit the water source of a hatchery and shed infectious spores of Aphanomyces invadans into the water. These can be readily transferred with transport water in which fry and fingerlings are sold.
©FAO/D. Huchzermeyer, Rhodes University
Properly dried, salted and iced fish have not been reported as potential carriers of EUS, therefore trade of these products can be allowed to continue.
Figure 39. Clarias gariepinus – African sharptooth catfish showing early and advanced lesions of epizootic ulcerative syndrome (EUS), Bangweulu swamps, north Zambia, 2014.
25
Can infection be prevented?
A
number of important biosecurity measures can minimize or prevent the spread of EUS. These include:
➔ All possible carriers or vectors such as freshly dead fish, birds or terrestrial animals as well as contaminated fishing gears/nets and fish transport containers should be prevented from getting into water bodies or fish ponds. ➔ In outbreaks occurring in small, closed water bodies, disinfection of destocked ponds by liming and improvement of water quality, together with removal of infected fish, are often effective in reducing mortality. ➔ Increasing salinity in holding waters to above 2 parts per thousand may also prevent outbreaks of EUS in aquaculture ponds. ➔ During dry and cold seasons, close observation of wild fish should be made to determine the presence of EUS–diseased fish in neighbouring tanks or canals, in which case, exchange of water should be avoided.
©FAO/D. Huchzermeyer, Rhodes University
➔ EUS infected fish should never be thrown back into open waters and should be disposed of properly by burying them into the ground or through incineration (burning).
Figure 40. Fish that have died as a result of epizootic ulcerative syndrome (EUS), such as this Clarias gariepinus, should be removed from the water. As the fish decays large numbers of Aphanomyces invadans spores can be released into the water, Bangweulu swamps, north Zambia, 2014.
26
➔ Additional practical aquaculture biosecurity measures should be implemented, including: – improved farm hygiene (e.g. handwashing between tanks, separation of nets/tanks/stocks, regular and correct disinfection procedures, etc.) – optimal husbandry practices – optimal water quality management – proper handling of fish – regular monitoring of fish health – good record keeping (gross and environmental observations and stocking records including movement records of fish in and out of the aquaculture facility, etc.) ➔ Early reporting or notification to concerned authorities of a disease outbreak or suspicion of any abnormal appearance, behaviour or other observations in fish stocks.
27
What can one do in the event of a disease outbreak? ➔ Immediately stop all live fish movements (quarantine). ➔ Dry and disinfect all fishing gear and boats before moving to another water body. ➔ Report immediately a suspected outbreak to concerned authorities (nearest fisheries or veterinary authority) and ask for guidance concerning collection of samples (see page 29). ➔ The abnormal congregation of aquatic birds feeding on fish has been typical of some outbreaks of EUS observed in Botswana and Zambia and may draw attention to presence of large numbers of sick fish. ➔ Taking note of simple observations that deviate from the normal will assist in Level I diagnosis and surveillance and will help to alert to presence of EUS. Abnormal swimming behavior such as swimming near the surface, swimming with the current, sinking to the bottom, loss of balance, flashing and cork-screw swimming and in non-airbreathing fish gulping at the surface are all indications of sick fish. If any of these observations are noted together with presence of red spots and ulcers/wounds on the fish this will be a strong indication of EUS. ➔ It is important to note the date and time of observed disease outbreaks to determine annual patterns during which fishermen and aquaculturists should be alert for the dangers of EUS. ➔ Further important information to record is the species of fish affected, an estimate of mortality (numbers of fish found dead) and the pattern of mortality (small number of fish dying each day, large number of fish dying at one time, etc.). ➔ Adverse climatic events such as flooding following on drought, sudden cold spells and the presence of disturbed soils that might cause acid leaching into waters should be recorded. ➔ Anticipation of outbreaks and early warning allow containment measures to be instituted timeously. These may include the need for additional disinfection of fishing equipment, discouraging fishermen from moving between EUSaffected and non-affected waters with their fishing gear, avoiding sourcing water for fish farms from water ways that might be contaminated with the zoospores of Aphanomyces invadans during an outbreak of EUS and avoiding moving fingerlings for fish farming from hatcheries on EUS-affected water sources. During an EUS outbreak, a ban on trade in fish across provincial and national borders and between catchments may be instituted by the authorities to reduce the spread of EUS.
28
Can I collect epizootic ulcerative syndrome (EUS) samples for laboratory examination? ➔ Live samples, if available, are best for laboratory examination. The fish should be packed in double plastic bags, filled with water to one third of their capacity with the remaining 2/3 volume inflated with air/oxygen. Bags should be tightly sealed (with rubber band or tape) and protected from temperature fluctuation. ➔ If live fish that can be transported to the laboratory are not available, freshly dead or moribund/sick fish with clinical lesions can be used. ➔ Using a scalpel or a blade, take samples of skin/muscle sections (<1 cm3), including the edge of the lesion and the surrounding tissue. Parts of internal organs may also be collected by dissecting the whole fish. ➔ Fix the tissue samples immediately in 10 percent formalin (10 ml of formalin in 90 ml of water, preferably phosphate-buffered saline made up in distilled water) in a plastic or bottled container. The amount of formalin should be 10 times the volume of the tissue to be fixed. Tissues should be fixed for at least 24 hours before processing. ➔ After 24 hours, fixed tissues can be wrapped into formalin-moistened tissue paper and placed into small plastic bags to prevent leakage or smell during transport. ➔ Using a scalpel or a blade, collect a second smaller sample of muscle (<0.5 cm3) from the edge of the lesion. ➔ Fix the muscle tissue immediately in 90-100 percent ethanol.
➔ Samples can be packed into a padded envelope or container and sent by mail if no courier services exist. ➔ Call the laboratory to inform of the kind of samples collected and when they are expected to arrive or to be delivered.
©FAO/D. Huchzermeyer, Rhodes University
➔ Make sure that samples are properly labelled with the following information: date of sampling, type of tissue samples (e.g. skin, muscle, gills, kidney, other internal organs), collection locality (place of collection), species of fish (weight and length measurements if possible), name of collector, type of fixative used (10 percent formalin, etc.). Figure 41. Positions relative to a typical epizootic ulcerative syndrome (EUS) lesion in Clarias gariepinus from which suitable samples can be dissected for fixation in (a) 10% formalin - sample should include skin and muscle and extend from the ulcer into surrounding healthy appearing tissue, and (b) 90-100% ethanol - the skin is removed and the underlying muscle is sampled adjacent to the edge of the ulcer or below the ulcer), Bangweulu swamps, north Zambia, 2014.
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References Andrew, T.G., Huchzermeyer, K.D.A., Mbeha, B.C. & Nengu, S.M. 2008. Epizootic ulcerative syndrome affecting fish in the Zambezi River system in southern Africa, Veterinary Record 163: 629–632. (also available at http://dx.doi.org/10.1136/vr.163.21.629,PMid:19029110). Baldock, F.C., Blazer, V., Callinan, R., Hatai, K., Karunasagar, I. Mohan, C.V. & Bondad-Reantaso, M.G. 2005. Outcomes of a short expert consultation on epizootic ulcerative syndrome (EUS): re-examination of causal factors, case definition and nomenclature. In P. Walker, R. Lester and M.G. Bondad-Reantaso (eds). Diseases in Asian Aquaculture V, pp. 555–585. Fish Health Section, Asian Fisheries Society, Manila. Blazer, V., Bondad-Reantaso, M.G., Callinan, R.B., Chinabut, S., Hatai, K., Lilley, J.H. & Mohan, C.V. 2005. Aphanomyces invadans (A. piscicida): A Serious Pathogen of Estuarine and Freshwater Fishes, pp. 24–41. In Cipriano, R.C., Shchelkunov, I.S. and Faisal, M. (editors). Health and Diseases of Aquatic Organisms: Bilateral Perspectives. Proceedings of the Second Bilateral Conference Between Russia and the United States. 21–18 September 2003. Sheperdstown, West Virginia. Michigan State University, East Lansing, Michigan. Bondad-Reantaso, M.G., McGladdery, S., East, I. & Subasinghe, R.P. (eds). 2001. Asia diagnostic guide to aquatic animal diseases. FAO Fisheries Technical Paper No. 402. Supplement 2. Rome, FAO. 240p. Choongo, K., Hang’ombe, B., Samui, K.L., Syachaba, M., Phiri, H. & Maguswi, C. 2009. Environmental and climatic factors associated with epizootic ulcerative syndrome (EUS) in fish from the Zambezi floodplains, Zambia. Bulletin of Environmental Contamination and Toxicology, 83: 474–478. (also available at http://dx.doi.org/10.1007/s00128-009-9799-0, PMid:19565173). FAO. 2009. Report of the international emergency disease investigation task force on a serious fish disease in Southern Africa, 18-26 May 2007. Rome, Italy. (also available at http://www.fao.org/ docrep/012/i0778e00.htm). FAO. 2017. Report of the International Emergency Fish Disease Investigation Mission on a Suspected Outbreak of Epizootic Ulcerative Syndrome (EUS) in the Democratic Republic of the Congo, 13–19 March 2015. Rome, Italy. (also available at http://www.fao.org/3/a-i6596e.pdf). Hatai, K., Nakamura, K., An Rha, S., Yuasa, K. & Wada, S. 1994. Aphanomyces infection in dwarf gourami (Colisa lalia). Fish Pathology., 29, 95–99 Huchzermeyer, K.D.A. & Van der Waal, B.C.W. 2012. Epizootic ulcerative syndrome: Exotic fish disease threatens Africa’s aquatic ecosystems. Journal of the South African Veterinary Association 83(1), Art. #204, 6 pages. (also available at http://dx.doi.org/10.4102/jsava.v83i1.204). Huchzermeyer, C.F., Huchzermeyer, K.D.A., Christison, K.W, Macey, B.M, Colly, P.A., Hangombe, B.M. & Songe M.M. 2017. First-record of epizootic ulcerative syndrome from the Upper Congo catchment: an outbreak in the Bangweulu swamps, Zambia. Journal of Fish Diseases. 41(1): 87-94, DOI:10.1111/jfd.12680 Kaphuka, B., Njunga, G. R., Kamwendo, G. & Chirwa, B. B. 2020. Active surveillance of infection caused by Aphanomyces invadans in Malawi. International Journal of Fisheries and Aquaculture (12) 1-5 (also available at http://doi: 10.5897/IJFA2019.0728). Lilley, J.H., Callinan, R.B., Chinabut, S., Kanchanakhan, S., MacRae, I.H. & Phillips, M.J. 1998. EUS Technical Handbook. AAHRI, Bangkok. 88pp. OIE. 2019. Manual of Diagnostic Tests for Aquatic Animals. World Organization for Animal Health, Paris. Malherbe, W., Christison, K.W., Wepener, V. & Smit, N.J. 2019. Epizootic ulcerative syndrome – First report of evidence from South Africa’s largest and premier conservation area, the Kruger National Park IJP: Parasites and Wildlife (10) 207-210 (also available at https://doi.org/10.1016/j. ijppaw.2019.08.007) McHugh, K.J., Christison, K.W., Weyl, O.L.F. & Smit, N.J. 2014. Histological confirmation of epizootic ulcerative syndrome in two cyprinid species from Lake Liambezi, Zambezi Region, Namibia. African Zoology 49(2), 311–316. Nsonga, A., Mfitilodze, W., Samui, K.L. & Sikawa, D. 2012. Epidemiology of epizootic ulcerative syndrome in the Zambezi River system. A case study for Zambia.Human and Veterinary Medicine. International Journal of the Bioflux Society, 5(1):1-8. Sibanda, S., Pfukenyi, D. M., Barson, M., Hang’ombe, B. & Matope, G. 2018. Emergence of infection with Aphanomyces invadans in fish in some main aquatic ecosystems in Zimbabwe: A threat to national fisheries production. Transboundary and Emerging Diseases: 1–9.DOI: 10.1111/ tbed.12922 Songe, M.M., Hang’ombe, M.B., Phiri, H., Mwase, M., Choongo, K., Van der Waal, B., Kanchanakhan, S., Reantaso, M. B. & Subasinghe, R. P. 2012. Field observations of fish species susceptible to epizootic ulcerative syndrome in the Zambezi River basin in Sesheke District of Zambia. Tropical Animal Health and Production, 44:179–183 DOI 10.1007/s11250-011-9906-1
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Glossary Disease
Any deviation from or interruption of the normal structure or function of any part, organ, or system (or combination thereof) of the body that is manifested by a characteristic set of symptoms and signs and whose aetiology, pathology and prognosis may be known or unknown.
Epidemiology
Science concerned with the study of the factors determining and influencing the frequency and distribution of disease or other health related events and their causes in a defined population for the purpose of establishing programmes to prevent and control their development and spread.
Epizootic
Affecting many animals at the same time; widely diffused and rapidly spreading disease (syn. Epidemic – used for human disease).
Epizootiology
The study of factors influencing infection by a pathogenic agent.
Fungi
Heterotrophic organisms possessing a chitinous* wall, with the majority of fungal species growing as multicellular filaments called hyphae forming a mycelium. Fungi are more closely related to animals than plants, yet the discipline of biology dedicated to the study of fungi, known as mycology, often falls under a branch of botany. * Note that in contrast to the true fungi, the oomycetes, of which Aphanomyces is a member, have a cellulose cell wall.
Granulomas
Any small nodular delimited aggregation of inflammatory cells, or modified macrophages resembling epithelial cells (epithelioid cells) formed by the body to ward off an infection or foreign substance.
Granulomatosis
Any condition characterized by the formation of multiple granulomas.
Heterokonts
Or stramenopiles are a major line of eukaryotes presently containing about 10 500 known species; includes the group oomycetes to which Aphanomyces invadans belongs. As opposed to higher fungi, the oomycetes have a cell wall composed of cellulose.
Infection
Invasion and multiplication of an infectious organism within host tissues. May be clinically benign (cf subclinical or carrier) or result in cell or tissue damage. The infection may remain localized, subclinical and temporary if the host defensive mechanisms are effective or it may spread to form an acute, subacute or chronic clinical infection (disease).
Lesion
Any pathological or traumatic change in tissue form or function.
Mycology
The study of fungi (Mycota).
Mycosis
Any disease resulting from infection by a fungus.
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Glossary
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Oomycetes
A group of filamentous, unicellular heterokonts or stramenopiles physically resembling fungi; they are microscopic, absorptive organisms that reproduce both sexually and asexually and are composed of mycelia. The genus Aphanomyces is known to produce only by asexual means.
Outbreak
The sudden onset of disease in epizootic proportions.
Pathogen
An infectious agent capable of causing disease.
Predispose
To make susceptible to a disease that may be activated by certain conditions, as by stress.
Sporangium
(Mycology) hyphal swelling which contains motile or non-motile zoospores; release is via a pore or breakdown of the sporangial wall (syn. zoosporangium).
Spore
Infective stage of an organism that is usually protected from the environment by one or more protective membranes (syn. zoospores).
Sporogenesis
Formation of or reproduction by spores; sporulation.
Stress
The sum of biological reactions to any adverse stimuli (physical, internal or external) that disturb the organism’s optimum operating status.
Susceptible
An organism which has no immunity or resistance to infection by another organism.
Syndrome
An assembly of clinical signs which when manifest together are indicative of a distinct disease or abnormality (syn. pathognomic/ pathognomonic).
Ulcer
Excavation of the surface of an organ or tissue, involving sloughing of necrotic inflammatory tissue.
©FAO/D. Huchzermeyer, Rhodes University
©FAO/D. Huchzermeyer, Rhodes University
Figure 44. Shallow vegetated areas of wetlands often harbour sick fish during an epizootic ulcerative syndrome (EUS) outbreak. Scoop nets are ideal for sampling such areas, Bangweulu swamps, north Zambia, 2014.
Figure 45. Bemba speaking fishermen with a seasonal catch of small flood plain fish being preserved by drying in the sun (traded as kasepa). During epizootic ulcerative syndrome (EUS) outbreaks, infected fish can readily be observed on drying racks, Bangweulu swamps, north Zambia, 2014.
©FAO/D. Huchzermeyer, Rhodes University
Figure 43. Typical catch of small fish species in a gill net left over night during surveillance for epizootic ulcerative syndrome (EUS)-affected fish, Chobe River, Botswana, 2007.
©FAO/D. Huchzermeyer, Rhodes University
Figure 42. Use of a sturdy scoop net is ideal for sampling small sick fish from the shallows along a river’s edge during an epizootic ulcerative syndrome (EUS) outbreak, Chobe River, Botswana, 2007.
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©FAO/D. Huchzermeyer, Rhodes University
©FAO/D. Huchzermeyer, Rhodes University
Figure 48. Searching for fish showing signs of epizootic ulcerative syndrome (EUS) in the shallows along a river bank. Note the red-brown colour of the water associated with low pH typical of waters draining from tropical rain forests, Equateur Province, Democratic Republic of Congo (DRC), 2015.
Figure 49. Rivers draining tropical rain forests in Africa often have a low pH of 4.5 favouring outbreaks of epizootic ulcerative syndrome (EUS), Equateur Province, Democratic Republic of Congo (DRC), 2015.
©FAO/D. Huchzermeyer, Rhodes University
Figure 47. Fishermen searching for epizootic ulcerative syndrome (EUS)-affected fish from a pirogue during an EUS investigation, Equateur Province, Democratic Republic of Congo (DRC), 2015.
©FAO/D. Huchzermeyer, Rhodes University
Figure 46. Inspecting live air-breathing fish for signs of epizootic ulcerative syndrome (EUS) at a fish market, Equateur Province, Democratic Republic of Congo (DRC), 2015.
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Fisheries - Natural Resources and Sustainable Production E-mail: Melba.Reantaso@fao.org www.fao.org/fishery
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