Abstract
Cormorant fishing is a traditional Japanese fishing method using captive Japanese cormorants (Phalacrocorax capillatus). Between June and July 2017, an avian pox outbreak was reported in captive cormorant populations throughout several distant cities in Japan. We examined the lesions obtained from two such affected cormorants, which were raised in distant cities. The affected cormorants were grossly characterized by the development of cutaneous nodules around the base of the beak. Histopathologically, these nodules consisted of marked epidermal hyperplasia with ballooning degeneration of spinous cells and eosinophilic intracytoplasmic inclusions (Bollinger bodies). The lesions displayed 4b core protein (P4b) of Avipoxvirus (APV) and DNA polymerase genes, which were detected by PCR. Moreover, the nucleotide sequences detected from both cormorants were found to be identical. No identical sequence was found in any international database. These findings suggest that both examined cormorants were infected with an identical APV, which has never been previously reported. According to the phylogenetic analysis, the detected sequences were observed to cluster in subclade A3, which consists mainly of the sequences detected from several marine birds, including other cormorant species. This observation suggests that the viruses might be maintained in Japanese cormorants in nature.