Oncorhynchus Masou Virus (OMV) Epidemiology and its Control Strategy

Distribution of salmonid herpesvirus was known in USA and Japan. Herpesviruses isolated in USA were classified to serotype 1 (SaHV-1) and in Japan were serotype 2 (SaHV-2). The reference strain of SaHV-1 is Herpesvirus salmonis and SaHV-2 is Oncorhynchus masou virus (OMV) strain OO-7812. OMV disease (OMVD) causes oncogenic and skin ulcer conditions. The main susceptible fish species are kokanee salmon (Oncorhynchus nerka), masu salmon (O. masou), coho salmon (O. kisutch) and rainbow trout (O. mykiss). Economic losses caused by this virus were recognized among kokanee salmon, coho salmon and rainbow trout. At the beginning of the 1980s, OMV was distributed widely in the northern part of Japan. Since 1988, OMV was isolated from coho salmon and since 1991 this virus was found in rainbow trout. Recently, re-appearing OMVD has become a major problem in pond culture of rainbow trout in the central part of Japan. OMV is sensitive to ultraviolet irradiation and iodophore treatment. Although detection of OMV in carrier fish is difficult using polymerase chain reaction (PCR) and OMV replicates and appears in ovarian fluid at mature stage, it can be controlled by disinfection. OMVD was successfully controlled by disinfection of all facilities and eggs with iodophore just after fertilization and again at early-eyed stage

The Epidemiological Study of Furunculosis in Salmon Propagation

The authors attempted to determine the distribution and prevalence of Aeromonas salmonicida in mature chum (Oncorhynchus keta), pink (O. gorbuscha), and masu salmon (O. masou) in Hokkaido that showed no apparent clinical signs of furunculosis. From September 1979 to November 1989, a total of 12,891 chum, pink, and masu salmon were collected from 30 rivers. The changing pattern of the annual prevalence of A. salmonicida in salmon was closely related to changes in fish density in the holding ponds: the prevalence of A. salmonicida increased in proportion to the increase in the number of fish in the ponds. We concluded from the results of histological and bacteriological examinations that fish with A. salmonicida in the kidney were not diseased but were carriers of A. salmonicida. The agent could not be isolated from the immature fish examined. A. salmonicida was also isolated from the ovarian fluid of fish showing no apparent clinical sign of furunculosis. Few A. salmonicida were found on the surface of the eggs one hour after fertilization. A survey of agglutination titers against A. salmonicida in sera of chum, pink, and masu salmon showed great variability within the species. The isolated strains were identified as A. salmonicida subsp. salmonicida and were pathogenic to salmonids. We concluded that the A. salmonicida carrier state in fish poses a serious problem in the prevention of furunculosis and its reduction plays a key role in salmon propagation. Both maturation of fish under conditions of low density in ponds, and disinfection of their eggs, are necessary to prevent fish furunculosis during artificial propagation of salmon.Nineteenth U.S.-Japan Meeting on Aquaculture. 29-30 October and 2 November 1990. Ise, Japan

An Epidemiological Study of Furunculosis in Salmon Propagation

Oji International Symposium on Salmonid Diseases. 22-25 October 1991. Sapporo, Japa

Prevalence of Aeromonas salmonicida, the causative agent of Furunculosis, among salmonid fish in Japan from 1979-2002

This study was carried out for the purpose of establishing control methods for furunculosis affecting propagated salmon in Japan. We determined the distribution and prevalence of A. salmonicida among asymptomatic adult chum (Oncorhynchus keta), pink (O. gorbuscha) and masu salmon (O. masou) returning to rivers on the island of Hokkaido and on the mainland of Honshu. During 1979-2002, a total of 22,109 chum, pink and masu salmon were collected from the rivers in Hokkaido and Honshu. We isolated A. salmonicida from the chum salmon in 21 of the 34 rivers examined and the overall prevalence was 12.2 % in the infected stocks. The prevalence of the agent in pink salmon and masu salmon was 4.6 % and 1.4 % respectively. Using CBB medium, we also examined the chum salmon from the Chitose River catching site. The prevalence of the agent on gill surface was high (50%) at the catching site and decreased among fish in the holding pond in the river. The bacteria appear to be spread during fish migration in the river and during transportation of the fish from the capture site to the holding pond. Recently, the agent was isolated from the gill surface of chum salmon caught off the coast of the eastern part of Hokkaido, but the prevalence was low (1.7%). To control furunculosis in salmonids, the fish should be held for maturation in ponds under conditions of low density and the fish should be disinfected to prevent spread of furunculosis before placement in the holding pond.10th International Symposium for Veterinary Epidemiology and Economics. 17-21 November 2003. Vina Del Mar, Chile

Detection of antibody against Aeromonas salmonicida in the serum of salmonid fish by the enzyme linked immunosorbent assay

Enzyme linked immunosorbent assay (ELISA) using the anti-masu Ig rabbit serum was applied to detect the antibody against Aeromonas salmonicida in the sera or salmonid fish. This ELISA method could detect the antibody in sera of masu (Oncorhynchus masou), chum (O. keta) and coho salmon (O. kisutch) immunized by A. salmonicida and could be applied to detect the antibody against A. salmonicida in sera of matured masu, pink (O. gorbuscha), chum, and kokanee salmon (O. nerka). In 1989, 89 masu and 250 chum salmon, and 59 kokanee were examined to detect antibody against A. salmonicida by ELISA and agglutination test. The number of the fish showing the positive reaction by ELISA, agglutination test and isolation of A. salmonicida were 262, 48, and 33, respectively. In 1990, 200 masu and kokanee salmon fry released from hatchery to river were tested and antibody against A. salmonicida was detected from 111 fish by ELISA, and the incidence of the fish showing the positive reaction was ranged from 4 to 90%

山形県において分離された自発凝集性を示さないAeromonas salmonicida

Auto-agglutination, protein staining of colonies and protein pattern of A-layer in thirty three isolates of Aeromonas salmonicida from salmonids in various parts of Yamagata Prefecture and Hokkaido were studied. The strains isolated in Yamagata Prefecture did not showed auto-agglutination in broth, colony colour was mainly grey-white on TSA-C and NA-C medium, and there was no 50 kDa. major protein band in the A-layer with SDS-PAGE. It was revealed from the results that non-agglutinating A. salmonicida exist in the strains isolated in Yamagata Prefecture. While there were no strains isolated in Hokkaido which were non-agglutinating. We suspect that the reason for the existence of non-agglutinating strains in Yamagata Prefecture may depend on the temperature at which this bacterium was isolated.山形県で分離された23株および北海道で分離された10株のAeromonas salmonicidaについて，液体培地での自発凝集性，Coomassie brilliant blueを添加した寒天培地上に発育したコロニーへの色素の吸着およびSDS-PAGEによるA-layerのタンパク組成を検討した．山形県で分離した株中4株は液体培地中で弱い自発凝集性を示し，寒天培地に出現したコロニーは主として色素の吸着を示さないコロニーであったが，一部のコロニーは吸着を示した．他の19株は全て自発凝集性を示さず，出現コロニーに色素の吸着は認められなかった．SDS-PAGEでは山形県での分離株は，北海道での分離株に見られた50kDa.の主要なタンパク質の存在は認められないか，微量であった．以上の結果から山形県での分離株には自発凝集を示さないA. salmonicidaが存在することが明らかになった