Epidemiology of Epizoootic Ulcerative Syndrome (EUS) on Fish in the Zambezi River System: A case study for Zambia

An epidemiological investigation was conducted from January to December 2011 in the Sesheke District of Zambia along the Zambezi River. The study aimed at determining factors associated with the outbreak of epizootic ulcerative syndrome (EUS), a newly confirmed disease in Southern Africa. The research also determined the prevalence, severity and distribution of EUS in the river. A total of 4,800 fish were inspected for gross EUS-like lesions while environmental factors were assessed to determined association with disease outbreak. Results of the study indicated that disease outbreak was preceded by heavy rains. The predominantly gleysol and arenosol soils of Zambezi river system resulted in low water pH (5.5 to 6.5); an ideal range for EUS causing agent to sporulate. Other factors significantly (P<0.05) associated with EUS outbreak were, low total alkalinity, water temperature, ambient temperature, month of sampling (June being significant) being associated with cold season, and site of sampling (lagoon and tributary being significant). Three percent of the smapled fish had typical characteristic lesions of EUS. Disease severity on fish ranged from mildness to healing wounds. Fifteen percent of the total sampled fish showed healing wounds while histopathological examinations showed mild infection by Brycinus lateralis, Serranochromis robustus and Sargochromis giardii. Participatory epidemiology revealed an upstream spread of EUS within the Zambezi river system.