In the present study, we describe a natural outbreak of carp edema virus disease (CEVD) in koi carp, concentrating on clinical manifestation, gross and microscopic pathology, immunological parameters, viral diagnostics, and phylogenetic analysis. Examination of white blood cell parameters showed increased monocyte and decreased lymphocyte counts in CEV-affected fish compared to healthy control fish. Regarding immune system functioning, the present work shows, for the first time, enhanced phagocytic activity in CEV-affected fish. Respiratory burst of phagocytes was strongly increased in diseased fish, the increase being attributed to an increased phagocyte count rather than enhancement of their metabolic activity. The present work also newly shows histopathological changes in the pancreatic tissue of diseased koi.

Department of Botany and Zoology Faculty of Science Masaryk University Brno 625 00 Brno Czech Republic

Department of Ecology and Diseases of Zoo Animals Game Fish and Bees Faculty of Veterinary Hygiene and Ecology University of Veterinary Sciences Brno Palackého tř 1946 1 612 42 Brno Czech Republic

Department of Experimental Biology Masaryk University 625 00 Brno Czech Republic

Department of Infectious Diseases and Preventive Medicine Veterinary Research Institute Brno 621 00 Brno Medlánky Czech Republic

Department of Zoology Fisheries Hydrobiology and Apiculture Mendel University in Brno 613 00 Brno Czech Republic

University of South Bohemia in České Budějovice Faculty of Fisheries and Protection of Waters South Bohemian Research Centre of Aquaculture and Biodiversity of Hydrocenoses Zátiší 728 2 389 25 Vodňany Czech Republic

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