Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aquaculture Viral interference between infectious pancreatic necrosis virus and spring viremia of carp virus in zebraﬁsh Melissa Bello-Perez a,1 , Regla Medina-Gali a,1 , Julio Coll b , Luis Perez a, ⁎ a Instituto de Biología Molecular y Celular, Universidad Miguel Hernández de Elche, 03202 Elche, Spain b Instituto Nacional de Investigaciones Agrarias, 28040 Madrid, Spain ARTICLE INFO Keywords: Zebraﬁsh IPNV SVCV Zebraﬁsh Viral interference ABSTRACT Fish birnaviruses and rhabdoviruses are major causes of diseases that pose a threat to the ﬁsh farming industry. In this work we investigated the interaction between IPNV (birnavirus) and SVCV (rhabdovirus) in a zebraﬁsh model where SVCV is lethal while IPNV causes asymptomatic infection. Two situations were analyzed: 1) A primary IPNV infection followed by a second challenge with SVCV; 2) SVCV as the ﬁrst infection and a second challenge with IPNV. Irrespective of the order of infections, IPNV increased survival of SVCV-infected ﬁsh, reﬂecting viral interference that correlated with the inhibition of SVCV RNA synthesis. In contrast, in some instances a synergistic eﬀect occurred between SVCV and IPNV: IPNV replication was enhanced in mixed in- fections with SVCV compared to the single IPNV infection. Expression of host immune response genes il1b, mx and gig2 was modulated diﬀerently depending on the order of virus infections: while higher levels of expression of il1b, mx and gig2 were found in ﬁsh infected ﬁrst with IPNV, those three genes were down-regulated in ﬁsh infected with SVCV and then challenged with IPNV. This ﬁrst report of mixed birnavirus/rhabdovirus infections in zebraﬁsh may help to identify those factors associated to disease resistance and cross-protection in ﬁsh, with practical implications for the development of new strategies for virus control in aquaculture. 1. Introduction Double or even multiple viral infections have been reported in several species of ﬁsh (Alonso et al., 2003; Kotob et al., 2016; Lin et al., 2017; Tafalla et al., 2006; Wiik-Nielsen et al., 2016). The study of the interplay between two viruses and its impact on the severity of disease and development of mortality in ﬁsh has shed some practical in- formation on the host responses to viral challenge that correlate to disease resistance and vaccine eﬃcacy (Emmenegger et al., 2017). Spring viremia of carp virus (SVCV) is the causative agent of spring viremia of carp disease. It belongs to the Rhabdoviridae family of viruses with negative sense single stranded RNA genome (Ashraf et al., 2016). Natural outbreaks of spring viremia of carp have been recorded in common carp and other cyprinid species (OIE, 2017). Infectious pancreatic necrosis virus (IPNV) causes disease in salmon and rainbow trout and has the ability to establish persistent infections in a number of ﬁsh species (Julin et al., 2014). IPNV is a member of the family Bir- naviridae, viruses with double-stranded RNA genome. Both IPNV and SVCV are present endemic in continental Europe (OIE, 2017). Thus, there is a possibility of IPNV and SVCV coexistence in ﬁsh, although dual IPNV/SVCV infections have not been encountered so far, it is perfectly possible due to the overlapping temperature range of both viruses and the ability of IPNV to infect a wide range of species. SVCV infection of zebraﬁsh by bath immersion has been extensively studied before (Encinas et al., 2013; Medina-Gali et al., 2018b; Sanders et al., 2003). Experimental infection of IPNV on zebraﬁsh has also been re- ported (Lapatra et al., 2000). Thus, from a practical point of view double IPNV/SVCV challenge of zebraﬁsh can be a suitable experi- mental model to study potential viral interference and host immune response in ﬁsh. When two viruses coincide in a host they often compete for the cellular machinery resulting in what is called viral interference. In ﬁsh, there is a body of evidence on IPNV-induced interference over other viruses both in vitro and in vivo. In cell culture, primary IPNV persis- tent infection blocks the replication of VHSV rhabdovirus in a sub- sequent infection (Garcia et al., 2011; Parreño et al., 2017). In vivo, IPNV infection often leads to the suppression of the secondary virus challenge (Byrne et al., 2008; Johansen and Sommer, 2001; Lopez- https://doi.org/10.1016/j.aquaculture.2018.10.039 Received 10 July 2018; Received in revised form 13 September 2018; Accepted 21 October 2018 ⁎ Corresponding author. 1 Both authors contributed equally to this work. E-mail addresses: melissa.bello@goumh.umh.es (M. Bello-Perez), luis.perez@umh.es (L. Perez). Aquaculture 500 (2019) 370–377 Available online 22 October 2018 0044-8486/ © 2018 Elsevier B.V. All rights reserved. T