The Outbreak of Koi Herpesvirus (KHV) in Koi (Cyprinus carpio koi) from Chiang Mai Province, Thailand

Twenty-two sick koi with cumulative mortality showed clinical signs of depression, brachial hemorrhage and necrosis, focal hemorrhage, pale patches and ulcers on the skin. Clinical examination showed the heavy infection by opportunistic organisms such as Dactylogyrus sp., Gyrodactylus sp. and Saprolegnia sp. of the skin, gill and fins. Histopathologically, the gill showed severe acute diffuse necrosis of the branchial epithelial cells and severe diffuse lymphocytic-monocytic interstitial nephritis with necrosis of the tubular epithelial cells were predominantly found in most sick fish. The presence of homogeneous pale basophilic intranuclear viral inclusions was observed. Transmission electron microscopy showed herpesvirus-like particles in the nuclei of gill epithelium. The positive result at 290 base pairs DNA product of KHV was confirmed from the gill samples using the polymerase chain reaction (PCR). In conclusion, this report confirmed the evidence of the outbreak of KHV in koi from Chiang Mai using pathology and molecular method.