Abstract
BackgroundThe infectious pancreatic necrosis virus (IPNV) causes significant economic losses in Chilean salmon farming. For effective sanitary management, the IPNV strains present in Chile need to be fully studied, characterized, and constantly updated at the molecular level.MethodsIn this study, 36 Chilean IPNV isolates collected over 6 years (2006–2011) from Salmo salar, Oncorhynchus mykiss, and Oncorhynchus kisutch were genotypically characterized. Salmonid samples were obtained from freshwater, estuary, and seawater sources from central, southern, and the extreme-south of Chile (35° to 53°S).ResultsSequence analysis of the VP2 gene classified 10 IPNV isolates as genogroup 1 and 26 as genogroup 5. Analyses indicated a preferential, but not obligate, relationship between genogroup 5 isolates and S. salar infection. Fifteen genogroup 5 and nine genogroup 1 isolates presented VP2 gene residues associated with high virulence (i.e. Thr, Ala, and Thr at positions 217, 221, and 247, respectively). Four genogroup 5 isolates presented an oddly long VP5 deduced amino acid sequence (29.6 kDa). Analysis of the VP2 amino acid motifs associated with clinical and subclinical infections identified the clinical fingerprint in only genogroup 5 isolates; in contrast, the genogroup 1 isolates presented sequences predominantly associated with the subclinical fingerprint. Predictive analysis of VP5 showed an absence of transmembrane domains and plasma membrane tropism signals. WebLogo analysis of the VP5 BH domains revealed high identities with the marine birnavirus Y-6 and Japanese IPNV strain E1-S. Sequence analysis for putative 25 kDa proteins, coded by the ORF between VP2 and VP4, exhibited three putative nuclear localization sequences and signals of mitochondrial tropism in two isolates.ConclusionsThis study provides important advances in updating the characterizations of IPNV strains present in Chile. The results from this study will help in identifying epidemiological links and generating specific biotechnological tools for controlling IPNV outbreaks in Chilean salmon farming.
Highlights
The infectious pancreatic necrosis virus (IPNV) causes significant economic losses in Chilean salmon farming
10 of the 36 Chilean IPNV isolates were classified within genogroup 1, a group that includes the North American isolates Jasper and West
The remaining 26 IPNV isolates were classified within genogroup 5 (72%), close to the European isolate Sp
Summary
The infectious pancreatic necrosis virus (IPNV) causes significant economic losses in Chilean salmon farming. Infectious pancreatic necrosis virus (IPNV) is the causative agent of a contagious fish disease by the same name and is responsible for economic losses in the aquaculture industry worldwide. In 2015, this viral agent represented about 30% of disease diagnoses reported from Chilean salmon farming centers and caused about 8% of pathogenassociated mortalities [1]. The transfer of young salmon to saltwater is a stressful stage, and high mortalities associated with IPNV outbreaks are commonly reported. Infected fish that overcome IPN remain asymptomatic carriers, with some authors reporting that the virus continues replicating in hematopoietic tissues [3,4,5]. Carrier fish could possibly be the most important mechanism through which this virus is maintained and remains contagious
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