It was recently reported that prophylaxis against infectious hematopoietic necrosis virus (IHNV) in fish was induced by pre-exposure to the infectious pancreatic necrosis virus (IPNV). Here the establishment of IHNV immunity in rainbow trout Oncorhynchus mykiss was investigated by IHNV challenge following non-lethal pre-infection with IPNV. Also, synthetic double-stranded RNA polyinosinic polycytidylic acid, Poly(I:C), an inducer for interferon (IFN), was evaluated as a substitute for IPNV induction of the non-specific antiviral state and subsequent IHNV-specific immunity in fish. Rainbow trout pre-infected with IPNV were protected from IHNV challenge 7 d later (relative percentage survival, RPS: 68.8%), and IHNV-specific antibodies were detected in sera from the survivors. Moreover, these surviving fish showed 91.6% RPS when re-challenged with IHNV 28 d after the primary IHNV challenge. Thus, fish appear to acquire IHNV-specific immunity through the IHNV challenge following pre-injection with IPNV. Fish pre-injected with Poly(I:C) were also highly protected from IHNV challenge 2 d later (RPS: 95.2%), and IHNV-specific antibodies were also detected amongst survivors. The survivors showed a 100% survival rate following re-challenge with IHNV both 21 and 49 d after the primary IHNV challenge. Thus, IHNV immunity in rainbow trout is induced by challenge with live IHNV following pre-injection with either IPNV or Poly(I:C). The use of Poly(I:C) to induce an anti-viral state protecting rainbow trout from an otherwise lethal vaccination dose of IHNV may have application to a wider range of fish species and fish pathogenic viruses.
KEY WORDS: Immunization · Infectious hematopoietic necrosis virus · IHNV · Poly(I:C) · Interferon · Antiviral state · Dual infection · Vaccine
Resale or republication not permitted without written consent of the publisherDis Aquat Org 83: [105][106][107][108][109][110][111][112][113] 2009 be more pathogenic in juveniles. The evolutionary divergence of IHNV influences its pathogenicity, but this has not been elucidated scientifically (Nishizawa et al. 2006a).In seed production facilities for salmonids, stable production of specific-pathogen-free (SPF) fish has been accomplished by measures for the prevention of IHNV transmission, such as disinfection of eggs with iodine, and sterilization of rearing water and facilities. Furthermore, maintenance of SPF-spawners monitored by antibody detection (ELISA) is also important and helpful to prevent vertical transmission of IHNV (Yoshimizu 1996(Yoshimizu , 2003. However, it is still difficult to prevent horizontal transmission of IHNV through water flow in rainbow trout farms. Therefore, development of an IHNV vaccine is essential, and several kinds of efficacious IHNV vaccines have been developed, e.g. killed or attenuated vaccines (Winton 1997, Biering et al. 2005, recombinant vaccines with IHNV G protein (Xu et al. 1991, Cain et al. 1999) and DNA vaccines with IHNV G gene (Anderson et al. 1996, Kim et al. 2000, Lorenzen et al. 2002.Prot...
