First report of carp oedema virus infection of koi (Cyprinus carpio haematopterus) in the Republic of Korea.

Twenty-five koi (Cyprinus carpio haematopterus) bought from a wholesale fish market in Korea, showed lethargic behaviour and 100% mortality within 20 days. Carp oedema virus (CEV) was detected by PCR in all 25 koi. Results of detailed histopathological and clinical examinations of 17 koi indicated loss of body balance, severe infiltration of inflammatory cells into the inter-lamellar spaces of the gills and vacuolization and inclusion bodies in gill epithelial cells. Sequence analysis of PCR products of these koi showed up to 99% identity to the previously reported sequences, suggesting that the observed mass mortality resulted from koi sleepy disease (KSD) due to CEV infection. To the best of our knowledge, this study is the first report of KSD in the Republic of Korea. Partial sequences of 4a protein from the virus indicated that the present CEV detected in koi from Korea is more closely related to that from the UK and Poland than from Japan. The present findings indicate that the prevalence and spread of KSD must be closely monitored in both European and Asian countries to avoid potential economic losses to the global koi industry.