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NO57 - 1

Vaccine Development against Cryptocaryoniasis: A Review

Yuho Watanabe and Tomoyoshi Yoshinaga*

Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

(Received August 17, 2021)

ABSTRACTCryptocaryon irritans is an obligate parasitic ciliate of marine teleosts and is the causative agent of cryptocaryoniasis (marine white spot disease). The parasite infects the skin and gills of marine teleosts and often causes mass mortality in heavily infected fish. Therefore, this parasite is a major threat to marine aquaculture in tropical and subtropical waters, and effective control methods are required. Interestingly, it was reported that fish infected with the parasite acquired protective immunity against it, and it was suggested that a vaccine strategy could be realized. Since then, many researchers have attempted to develop vaccines against cryptocaryoniasis. This review presents the current research on vaccine development against cryptocaryoniasis to provide references for future experimental studies and propose future research directions.

Key words: Cryptocaryon irritans, cryptocaryoniasis, marine white spot disease, vaccinology, i-antigens

Asymptomatically Infected Broodstock are a Potential Infection Source for Aquareovirus Outbreaks in Hatchery-reared Japanese Flounder Paralichthys olivaceus

Yasuhiko Kawato1*, Tomoki Maeda2, Toyohiro Nishioka3, Ikunari Kiryu1, Tohru Mekata1, Tomomasa Matsuyama1, Kozue Tensha4, Isao Yamashita5, Yoshihiro Kawamura6, Atsushi Raku7, Kei Senbokuya8, Soetsu Yanagi9, Kyoji Hayashi10, Kyoji Hayashi11 and Koh-ichiro Mori12

1Pathology Division, Nansei Field Station, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Mie 519-0193, Japan
2Pathology Division, Tamaki Field Station, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Mie 519-0423, Japan
3Yashima Field Station, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Kagawa 761-0111, Japan
4Agriculture, Forestry and Fisheries Department, Yamaguchi Prefectural Government, Yamaguchi 753-8501, Japan
5Yamaguchi Prefectural Sea Farming Public Corporation, Yamaguchi 759-4107, Japan
6Hyogo Prefectural Agriculture, Forestry and Fishery Technology General Center, Hyogo 674-0093, Japan
7Hyogo Abundant Sea Association, Hyogo 674-0093, Japan
8Ishikawa Prefecture Fisheries Research Center, Ishikawa 927-0435, Japan
9Kagoshima Prefectural Fisheries Promotion Section, Kagoshima 890-8577, Japan
10Oita Prefectural Agriculture, Forestry and Fisheries Research Center, Oita 879-2602, Japan
11Miyagi Prefecture Fisheries Technology Institute, Miyagi 986-2135, Japan
12Nagasaki Field Station, Fisheries Technology Institute, Japan Fisheries Research and Education Agency, Nagasaki 851-2213, Japan

(Received July 6, 2021)

ABSTRACT―Aquareovirus infection by hirame aquareovirus (HAqRV) is fatal in hatchery-reared Japanese flounder Paralichthys olivaceus. In the present study, we investigated the transmission route of HAqRV in order to develop outbreak prevention measures. HAqRV was isolated from six cases of Japanese founder juveniles from different locations in 2015 and 2016 and compared by molecular epidemiology. For three of these cases, apparently healthy broodstock that were used for Japanese flounder production were subjected to virus carrier tests using real-time PCR and ELISA targeting the viral genome and antibody against HAqRV, respectively. The viral genome was detected in the intestine and/or liver, with a detection rate of approximately 60% (n = 143). For the ELISA test, antibodies against HAqRV were detected in 100% of the examined broodstock (n = 109). Sequencing analysis of the RNA-dependent RNA polymerase gene indicated that the nucleotide sequences of the isolated virus, diseased juveniles, and apparently healthy adults were identical within the same case, but distinct among different cases. These results suggest that asymptomatically infected broodstock are a potential infection source of HAqRV outbreaks in Japanese flounder juveniles.

Key words: Aquareovirus, HAqRV, flounder, Paralichthys olivaceus, broodstock, infection source, transmission route

The First Report of Loma salmonae (Microsporidia) in Cultured Yamame Trout Oncorhynchus masou masou in Japan

Ryo Inoue1* and Tetsuya Yanagida2

1Tokyo Metropolitan Islands Area Research and Development Center for Agriculture Forestry and Fisheries, Tokyo 105-0022, Japan
2Laboratory of Veterinary Parasitology, Joint Faculty of Veterinary Medicine, Yamaguchi University, Yamaguchi 753-8511, Japan

(Received August 3, 2021)

ABSTRACT―In 2019, a large number of microsporidian xenomas was confirmed in the gills of yamame trout (landlocked masu salmon), Oncorhynchus masou masou, cultured in Tokyo. The spore size was similar to that of the previously reported Loma salmonae, and the nucleotide sequence of the ribosomal RNA gene (1,839 bp) showed 99.9% similarity with that of L. salmonae from Oncorhynchus spp. in North America. Based on the morphological and molecular analyses, the microsporidian from yamame trout was identified as L. salmonae. During October 2019 to July 2021, four cases of L. salmonae infection in yamame trout were confirmed at three fish farms in Tokyo. Loma salmonae is the causative agent of microsporidial gill disease in salmonids, causing economic losses in salmonid aquaculture in North America and Europe. In Japan, Loma sp. was once reported from O. masou masou in Hokkaido, but it was not identified at the species level. This is the first confirmed report of L. salmonae infections in Japan, and also its new host record from O. masou masou.

Key words: new locality, Loma salmonae, new host, Oncorhynchus masou masou, case report

The Nasal Cavity of Red Sea Bream Pagrus major is an Important Entry Site for Edwardsiella anguillarum

Takumi Endo1, Shin-Ichi Kitamura1*, Hidemasa Kawakamii2 and Takaji Iida3

1Center for Marine Environmental Studies, Ehime University, Ehime 790-8577, Japan
2Ehime Fisheries Research Center, Ehime 798-0087, Japan
3Faculty of Veterinary Medicine, Okayama University of Science, Ehime 794-8555, Japan

(Received October 14, 2021)

ABSTRACT―The location Edwardsiella anguillarum causing edwardsiellosis in red sea bream Pagrus major enters the fish is hypothesized to be the nasal cavity because ulcers form on the head. To test this hypothesis, we conducted two infection experiments on red sea bream. Fish were inoculated with a bacterial suspension in each nasal cavity, the cumulative mortality plateaued at 60-70%. Fish had its nasal cavities obstructed were challenged by immersion infection, the cumulative mortality was significantly lower than control group. These results strongly suggest that the nasal cavity of fish is an important entry site for E. anguillarum.

Key words: nasal cavity, entry site, edwardsiellosis, Edwardsiella anguillarum, red sea bream