title: Epizootic ulcerative syndrome: exotic fish disease threatens Africa's aquatic ecosystems.
abstract: In late 2006 an unusual ulcerative condition in wild fish was reported for the first time in Africa  from the Chobe and upper Zambezi Rivers in Botswana and Namibia. Concern increased  with subsistence fishermen reporting large numbers of ulcerated fish in their catches. In April  2007 the condition was confirmed as an outbreak of epizootic ulcerative syndrome (EUS).  The causative agent, Aphanomyces invadans, is a pathogenic water mould of fish that shows  little host specificity. Ulcers follow infection of tissues by oomycete zoospores, resulting in  a granulomatous inflammation associated with invading oomycete hyphae. Granulomatous  tracts surrounding oomycete hyphae within the necrotic tissues characterise the diagnostic  histological picture. The upper Zambezi floodplain at the confluence with the Chobe River  spans the four countries of Botswana, Namibia, Zambia and Zimbabwe, making disease control  a challenge. The floodplain ecosystem supports a high fish diversity of around 80 species,  and is an important breeding and nursery ground. The annual cycle of flooding brings about  changes in water quality that are thought to favour the infectivity of A. invadans, with diseased  fish appearing soon after the plains become flooded. Since 2006 the disease has spread rapidly  upstream along the upper Zambezi and its tributaries. By 2010 the disease was reported from  the Okavango Delta in Botswana and in 2011 from the Western Cape Province of South Africa.  EUS has the potential to disrupt floodplain ecosystems elsewhere in Africa where high fish  diversity forms the basis of subsistence fisheries and local economies, and is a direct threat to  freshwater fish culture.
authors: Sterkspruit Veterinary Clinic, Lydenburg, South Africa. aquavet@telkomsa.net
authors: Karl D A
authors: KD
authors: Huchzermeyer
authors: Benjamin C W
authors: BC
authors: van der Waal
mesh_terms: D000349:Africa / Q000453:epidemiology; D000818:Animals; D044744:Aphanomyces; D004196:Disease Outbreaks; D004198:Disease Susceptibility; D017753:Ecosystem; D005393:Fish Diseases / Q000453:epidemiology*; D005399:Fishes; D007239:Infections / Q000453:epidemiology / Q000662:veterinary*; D045483:Rivers; D013045:Species Specificity