Epizootic ulcerative syndrome affecting fish in the Zambezi river system in southern Africa

Abstract

In late 2006, diseased fish of a variety of species began to appear in the Chobe and upper Zambezi rivers in southern Africa. In April 2007, investigations showed that the levels of pesticides and heavy metals in the tissues of the fish were very low, discounting pollution as an underlying cause for the disease. However, histological evidence showed that the disease closely resembled the epizootic ulcerative syndrome caused by the oomycete Aphanomyces invadans, a serious aquatic pathogen that has been isolated from freshwater and estuarine fish in Japan, south-east Asia, Australia and the usa since the 1970s, but not previously recorded in Africa.

Aphanomyces sinensis sp. nov., isolated from juvenile soft-shelled turtle, Pelodiscus sinensis, in Japan

“…Later, A. invadans Willoughby, Roberts & Chniabut was reported as the causative agent of epizootic ulcerative syndrome (EUS) in Thailand (Willoughby et al 1998). Furthermore, some diseases caused by the same fungus were found in some fishes from Southeast Asian countries (Willoughby and Roberts 1994;Lilley et al 1998) and in sand whiting Sillago ciliate from South Africa (Andrew et al 2008). Similarly, A. invadans was found to cause ulcerative mycosis in Atlantic menhaden Brevoortia tyrannus from the United States (Dykstra et al 1986) and red spot disease (RSD) in sea mullet Mugil cephalus and yellowfin bream Acanthopagrus australis from Australia (Fraser et al 1992).…”

A new species, Aphanomyces salsuginosus sp. nov., isolated from ice fish Salangichthys microdon

“…invadans Willoughby, R.J. Roberts & Chinabut (also called A. piscicida Hatai) was first reported as the pathogen causing mycotic granulomatosis in ayu Plecoglossus altivelis in Japan (Hatai 1980). Later, A. invadans was identified as the cause of epizootic ulcerative syndrome (eEUS) in some fishes from Southeast Asian countries (Willoughby and Roberts 1994;Lilley et al 1998) and in sand whiting Sillago ciliate from South Africa (Andrew et al 2008). Similarly, A. invadans was found to cause ulcerative mycosis in Atlantic menhaden Brevoortia tyrannus from the USA ) and red spot disease (RSD) in sea mullet Mugil cephalus and yellowfin bream Acanthopagrus australis from Australia (Fraser et al 1992).…”

Scientific Opinion on Epizootic Ulcerative Syndrome

“…An ulcerative mycosis was observed in estuarine fish along the east coast of the United States in 1978 (and perhaps before) (Noga and Dykstra, 1986) and since then the disease has been repeatedly reported from the USA in a wide range of species. EUS was found on the African continent for the first time in 2006 (Andrew et al, 2008;FAO, 2009). No reports are yet published showing the presence of the disease in Europe or South America.…”