Identification of envelope protein pORF81 of koi herpesvirus

Koi herpesvirus (KHV), an emerging pathogen causing mass mortality in koi and common carp, possesses the largest known herpesvirus genome of 295 kbp predicted to encode 156 different proteins. However, none of them has been identified or functionally characterized up to now. In this study, a rabbit antiserum was prepared against a bacterial fusion protein that permitted detection of the predicted type III membrane protein encoded by ORF81 of KHV. In Western blot analyses, the abundant ORF81 gene product of KHV exhibited an apparent mass of 26 kDa and appeared to be non-glycosylated. It could be localized in the cytoplasm of infected cells and in virion envelopes by indirect immunofluorescence and immunoelectron microscopy, respectively. The antiserum was also suitable for the detection of pORF81 in sections of gills, kidneys, hepatopancreas and skin of KHV-infected carp by immunohistochemistry.