Viral hemorrhagic septicemia (VHS) is one of the most serious
viral diseases in rainbow trout (Oncorhynchus mykiss) in continental
European countries [1] and has been reported in several
other marine and freshwater fish species worldwide [2]. Moreover,
VHS is listed as a notifiable disease by the World Organization for
Animal Health (OIE) [3]. The causative agent of VHS, the VHS virus
(VHSV), is a member of the genus Novirhabdovirus in the family
Rhabdoviridae [4]. VHSV is classified into 4 genogroups (IeIV) based
on species and geographical distribution [4,5]. In Korea, VHSV was
first reported in juvenile olive flounder at an aquaculture farm in
2001 [6]. Since 2001, outbreaks have been reported often in olive
flounder farms throughout Korea.
Despite the importance of VHS from an economic standpoint, no
vaccine against VHSV is commercially available [3]. Research aimed
at developing a vaccine against VHSV has been conducted for
several years, resulting in killed and attenuated vaccines, recombinant
proteins, and DNA vaccines using VHSV glycoprotein [7e12].
Among commonly used types of vaccines, formalin-inactivated
* Corresponding author.
E-mail address: srkwon@sunmoon.ac.kr (S.R. Kwon).
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Fish & Shellfish Immunology
journal homepage: www.elsevier.com/locate/fsi
http://dx.doi.org/10.1016/j.fsi.2015.11.035
1050-4648/© 2015 Elsevier Ltd. All rights reserved.
Fish & Shellfish Immunology 48 (2016) 206e211
vaccines are frequently used due to the high safety offered by
formalin treatment, which kills the pathogen in the vaccine.
Recently, it was reported that inoculation with polyinosinicpolycytidylic
acid (Poly(I:C)) and a live pathogenic virus, a
method known as poly(I:C) immunization, produced a strong
protective effect against VHSV in fish and elicited a specific immune
response against the virus [13e19].
Induction of a specific antibody response against a target
pathogen may be confirmed by challenging vaccinated fish with the
pathogen of interest and detecting specific antibodies in the sera by
enzyme-linked immunosorbent assay (ELISA). However, antibody
detection by ELISA in fish has poor reproducibility due to various
factors, including the strong background signal caused by nonspecific
interactions between fish antibodies and antigens
[20e26]. Recently, an improved ELISA was developed, in which the
non-specific response in vaccinated fish was reduced using cell
culture supernatants [27,28].
In the present study, the efficacy of Poly(I:C) immunization with
a live vaccine against VHSV was compared with that of a formalinkilled
vaccine in olive flounder.