Why has infectious hematopoietic necrosis virus been changing into more virulent? – identification of the factors causing the virus change

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H03046
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 40040:Aquatic life science-related
• Research Institution: Tokyo University of Marine Science and Technology
• Principal Investigator: SANO Motohiko 東京海洋大学, 学術研究院, 教授 (00372053)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: ニジマス養殖 / ウイルス病 / 伝染性造血器壊死症 / 強毒化 / 強毒化要因 / 持続感染 / 再活性化 / 親魚ウイルス保有

Outline of Final Research Achievements

The objective of this study is to elucidate the factors behind the recent increase of virulence of infectious hematopoietic necrosis (IHN) virus. Virus isolates from dead rainbow trout fry tended to show strong virulence to the fry strain from which they were isolated, and the virus might be less sensitive to interferon of the fish strain. Many isolates from ovarian fluid of spawning fish were low virulent. Persistent virus infection was more likely to occur in infected fish with a low mortality rate and blood antibodies against the virus can be involved in suppressing the persistent infection. Adult fish were found to be re-infected with the virus just before spawning when their immunity was suppressed. These results suggests that persistent infection occurs in the juvenile fish surviving in a primary infection with low virulent virus, resulting in appearance of virus diversity in the fish during the growing up period and consequently emerging of highly virulent viruses.

Free Research Field

水族病理学

Academic Significance and Societal Importance of the Research Achievements

近年、ニジマス海面養殖は、企業参入が相次ぎ、大きな期待が寄せられているが、依然として伝染性造血器壊死症（IHN）がニジマス養殖に大きな被害を与え続けている。以前は小さな稚魚だけの被害であったが、近年では100g以上の魚も死亡するようになり、ウイルスの強毒化が大きな脅威であり、ニジマス養殖振興にはこの抑制が喫緊の課題である。本研究の結果、今まで想像されていた親魚でのウイルスの変異・強毒化ではなく、死亡の少なかった稚魚群の育成期間にわたる持続感染によってウイルス変異が起きると推察された。これ以上の強毒化阻止には、稚魚期のウイルス接触を防止するとともに、ワクチン等の予防手段の開発が必要と考えられた。