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NO47 - 4

Protective Efficacy of a Formalin-inactivated Vaccine against Viral Hemorrhagic Septicemia in Japanese Flounder Paralichthys olivaceus

Tadashi Isshiki1*, Takeya Morimoto1, Masahiro Iwasaki1, Masaaki Abe2, Taizou Nagano2, Takashi Hazama3,
Jun-Young Song3** and Shin-Ichi Kitamura3
1Graduate School of Bioresources, Mie University, Mie 514-8507, Japan
2Kagawa Prefectural Fisheries Experimental Station, Kagawa 761-0111, Japan
3Center for Marine Environmental Studies, Ehime University, Ehime 790-8577, Japan

(Received June 2, 2012)

ABSTRACT─We examined the effectiveness of a formalin-inactivated vaccine against viral hemorrhagic septicemia (VHS) in Japanese flounder Paralichthys olivaceus by the pathogen challenge. Japanese flounder (average weight, 10 g) kept at 12°C, 20°C and 28°C were vaccinated by intraperitoneal injection of a formalin-inactivated VHS virus (VHSV) and maintained at each temperature for 21, 19 and 17 days post vaccination (dpv), respectively. The fish vaccinated at 20°C and 28°C were acclimated to 12°C, and then all vaccinated fish were challenged with VHSV at 12°C at 21 dpv. Fish that received the vaccine at 20°C showed relative percent survival (RPS) of 48%, compared with 0% for those given the vaccine at 12°C and 28°C. In other experiment, efficient protection against VHSV lasted at least 7 mo in Japanese flounder (average weight, 100 g) vaccinated at 20°C and maintained at ambient temperature, where high RPS values (71-100%) were obtained after viral challenges at 18, 77, 98 and 213 dpv. We obtained promising results that a single immunization with the formalin-inactivated vaccine at the physiologically optimal temperature (20°C) provided significant protective and long-lasting immunity to Japanese flounder against VHS.

Key words: Viral hemorrhagic septicemia virus, VHSV, Paralichthys olivaceus, vaccination, formalin-inactivated vaccine, water temperature, long-lasting immunity

Surveillance of Type 1 Ostreid Herpesvirus (OsHV-1) Variants in Japan

Yoshiko Shimahara1, Jun Kurita1**, Ikunari Kiryu1, Toyohiro Nishioka1, Kei Yuasa1, Morihiko Kawana2, Takashi Kamaishi1 and Norihisa Oseko1*
1National Research Institute of Aquaculture, Fisheries Research Agency, Mie 519-0193, Japan
2Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Hokkaido 062-0992, Japan

(Received July 5, 2012)

ABSTRACT─Ostreid herpesvirus 1 (OsHV-1) μVar is a variant of OsHV-1 and suspected of being the causative agent of acute mass mortality events of Pacific oysters during summers in Europe since 2008. In this study, the distribution of OsHV-1 was surveyed in the six main oyster-producing areas of Japan, using PCR targeting a C2/C6 fragment including ORF4. PCR products were amplified from 123 out of 1,714 oysters of three species of Crassostrea (C. gigas, C. sikamea and C. ariakensis), and 23 different nucleotide sequences, showing 96% to 99% similarity to the reference OsHV-1, were obtained. Although 18 sequences among the 23 obtained possessed a microsatellite deletion unique to OsHV-1 μVar, all PCR products contained two conserved nucleotides that were shared with the reference OsHV-1 and not with OsHV-1 μVar. Here, we found variable types of OsHV-1 in oysters in Japan, but their nucleotide sequences were not identical to those of OsHV-1 μVar.

Key words: Ostreid herpesvirus, OsHV-1, OsHV-1 μVar, Crassostrea gigas, C. sikamea, C. ariakensis, Japan, Pacific oyster

RSIV is Probably Insensitive to the Transient Innate Immune Response Induced by Administration of Poly(I:C), a Synthetic Double-Stranded RNA

Jong-Oh Kim, So-Young Oh, Takanori Matsui, Myung-Joo Oh and Toyohiko Nishizawa*
Department of Aqualife Medicine, Chonnam National University, Yeosu 550-749, Republic of Korea

(Received September 8, 2012)

ABSTRACT─Red seabream iridovirus (RSIV) causes significant mortality in many marine fishes. Polyinosinic-polycytidylic acid [Poly(I:C)] immunization with a live virus confers protection of fishes from viral infection. Thus, we applied this immunization with live RSIV to rock bream Oplegnathus fasciatus, red seabream Pagrus major and yellowtail Seriola quinqueradiata. No significant difference was observed in mortalities due to RSIV infection between the fishes that did or did not receive Poly(I:C), indicating that fishes administered Poly(I:C) were not protected from RSIV infection. It was confirmed that the Mx gene, an indicator of induced interferon, was well expressed in rock bream that received Poly(I:C). The results suggest that RSIV is probably insensitive to the transient innate immune response induced by Poly(I:C).

Key words: red seabream iridovirus, megalocytivirus, interferon, Poly(I:C), RSIV, innate immune response

Ichthyodinium Infection in the Embryos and Yolk Sac Larvae of Pacific Bluefin Tuna Thunnus orientalis

Katsuya Ishimaru1*, Naoki Iida1, Takahiko Okada2 and Shigeru Miyashita1
1Fisheries Laboratory, Kinki University, Wakayama 649-2211, Japan
2Fish Nursery Center, Kinki University, Wakayama 649-2211, Japan

(Received May 9, 2012)

ABSTRACT─In July 2003, we observed abnormal opaqueness of both the yolk in the embryos and recently hatched larvae of Pacific bluefin tuna Thunnus orientalis spawned at the Ohshima Experimental Station in Wakayama, Japan. The yolks were infected with a number of a unicellular parasite. All the infected yolk sacs burst one day post-hatch. Consequently, all the host larvae died and the parasites were released into seawater. The infection rate of this disease was less than 16% in 2003 but spiked up to 98% in 2004. However, the disease has not been observed since 2006. The pathogen has been identified as Ichthyodinium sp. belonging to Alveolata.

Key words: Ichthyodinium chabelardi, endoparasite, Thunnus orientalis, Pacific bluefin tuna, yolk sac larvae