The Status of Viral Diseases of Carp in Korea: Its Control and
Research Development

Mi-Young Cho¹, Sang-Kyu Shon² and Soo-II Park<sup>3

1</sup>Pathology Team, National Fisheries R & D Institute (NFRDI)
²Aquaculture and Environment Institute, NFRDI
³Department of Aquatic Life Medicine, Pukyoung National University

ABSTRACT

The carp (Cyprynus carpio) is the most common species of cultured fish, in particular, common carp and Israel carp have been cultured as an edible fish for several decades in Korea. Viral diseases of carp have never been reported until 1988 despite its long aquaculture history in Korea. However, mass mortality occurred in populations of cultured carp from 1988 to 1999 resulting in a drastic reduction of production in Korea. The infected fish showed dark coloration, excessive mucus secretion from the surface and gills and branchial necrosis. Several cases were reported that dermal ulcers were noticed due to secondary infection with bacteria or parasites. Oh et al. (2001) reported that the virions with 70-80nm in diameter were presumed to be a causative virus in the kidney and spleen tissues of infected fish. They also have reported that the artificial infection using a viral suspension of 103TCID50/mL obtained from the infected FHM cells, produced 80 to 100 percent mortality in carp. Kim et al. (2003), as a result of conducting gene cloning of the virus, suggested that the virus being a new species different from the known reported viruses of carps such as grass carp reovirus (GCRV), grass carp hemorrhage virus (GCHV), koi herpesvirus (KHV) and spring vireamia of carp virus (SVCV). Unlikely such findings, Choi et al. (2003) found a herpes-like virus of 82 nm size within the nucleus of spleen cells from infected carp.

During the past three years, the present study was established to develop the prevention technologies for epidemics in order to protect the carps from the viral disease. Two types of inactivated vaccines were prepared with the viral suspension that was obtained from the infected FHM cells: formalin-killed vaccine (FKV) and heat-killed vaccine (HKV). The lysozyme activity of serum and chemiluminescent responses of head-kidney leucocytes showed increasing in the vaccinated fish, and as measured by ELISA, vaccinated groups showed a significant increasing in the virus-specific serum antibodies. Results of the virus challenge showed that the fish vaccinated with FKV have induced protective immunity, while HKV injection hardly provided protection. And the antiviral activity of carp was examined using the interferon inducers such as poly inosinic: cytidylic acid (Poly I:C) and SVCV. The results showed that carp pretreated with Poly I:C developed an anti-viral protection, which resulted in lower cumulative mortality against SVCV when comparing to untreated fish.

Since 1998, many studies have been conducted in diversified aspects to find out the causative virus of the diseases and prevention measures against viral disease of carp in Korea. However, identification of the virus was not clear and effective control measures were not established so far. Therefore, further studies on the causative virus including characterization and infection mechanisms are required.