title: Infectious salmon anaemia virus (ISAV) in Chilean Atlantic salmon (Salmo salar) aquaculture: emergence of low pathogenic ISAV-HPR0 and re-emergence of virulent ISAV-HPR∆: HPR3 and HPR14.
abstract: Infectious salmon anaemia (ISA) is a serious disease of marine-farmed Atlantic salmon (Salmo salar) caused by ISA virus (ISAV), which belongs to the genus Isavirus, family Orthomyxoviridae. ISA is caused by virulent ISAV strains with deletions in a highly polymorphic region (HPR) of the hemagglutinin-esterase (HE) protein (designated virulent ISAV-HPR∆). This study shows the historic dynamics of ISAV-HPR∆ and ISAV-HPR0 in Chile, the genetic relationship among ISAV-HPR0 reported worldwide and between ISAV-HPR0 and ISAV-HPR∆ in Chile, and reports the 2013 ISA outbreak in Chile. The first ISA outbreak in Chile occurred from mid-June 2007 to 2010 and involved the virulent ISAV-HPR7b, which was then replaced by a low pathogenic ISAV-HPR0 variant. We analyzed this variant in 66 laboratory-confirmed ISAV-HPR0 cases in Chile in comparison to virulent ISAV-HPR∆ that caused two new ISA outbreaks in April 2013. Multiple alignment and phylogenetic analysis of HE sequences from all ISAV-HPR0 viruses allowed us to identify three genomic clusters, which correlated with three residue patterns of ISAV-HPR0 (360PST362, 360PAN362 and 360PAT362) in HPR. The virus responsible for the 2013 ISAV-HPR∆ cases in Chile belonged to ISAV-HPR3 and ISAV-HPR14, and in phylogenetic analyses, both clustered with the ISAV-HPR0 found in Chile. The ISAV-HPR14 had the ISAV-HPR0 residue pattern 360PAT362, which is the only type of ISAV-HPR0 variant found in Chile. This suggested to us that the 2013 ISAV-HPR∆ re-emerged from ISAV-HPR0 that is enzootic in Chilean salmon aquaculture and were not new introductions of virulent ISAV-HPR∆ to Chile. The clinical presentations and diagnostic evidence of the 2013 ISA cases indicated a mixed infection of ISAV with the ectoparasite Caligus rogercresseyi and the bacterium Piscirickettsia salmonis, which underscores the need for active ISAV surveillance in areas where ISAV-HPR0 is enzootic, to ensure early detection and control of new ISA outbreaks, as it is considered a risk factor. This is the first report of ISA linked directly to the presence of ISAV-HPR0, and provides strong evidence supporting the contention that ISAV-HPR0 shows a strong relationship to virulent ISAV-HPR∆ viruses and the possibility that it could mutate to virulent ISAV-HPR∆.
authors.forename: Marcos G
authors.initials: MG
authors.lastname: Godoy
authors.forename: Molly J T
authors.initials: MJ
authors.lastname: Kibenge
authors.forename: Rudy
authors.initials: R
authors.lastname: Suarez
authors.forename: Eduardo
authors.initials: E
authors.lastname: Lazo
authors.forename: Alejandro
authors.initials: A
authors.lastname: Heisinger
authors.forename: Javier
authors.initials: J
authors.lastname: Aguinaga
authors.forename: Diego
authors.initials: D
authors.lastname: Bravo
authors.forename: Julio
authors.initials: J
authors.lastname: Mendoza
authors.forename: Katerina O
authors.initials: KO
authors.lastname: Llegues
authors.forename: Rubén
authors.initials: R
authors.lastname: Avendaño-Herrera
authors.forename: Cristian
authors.initials: C
authors.lastname: Vera
authors.forename: Fernando
authors.initials: F
authors.lastname: Mardones
authors.affiliation: Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Ave, Charlottetown, P,E,I,, C1A 4P3, Canada. kibenge@upei.ca.
authors.forename: Frederick S B
authors.initials: FS
authors.lastname: Kibenge
mesh_terms: D000818:Animals; D017756:Aquaculture; D002677:Chile / Q000453:epidemiology; D016000:Cluster Analysis; D005393:Fish Diseases / Q000453:epidemiology / Q000821:virology*; D005838:Genotype; D046829:Isavirus / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D017720:Molecular Epidemiology; D008969:Molecular Sequence Data; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000662:veterinary* / Q000821:virology; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics; D020317:Salmo salar / Q000821:virology*; D017422:Sequence Analysis, DNA
chemical_list: D012367:RNA, Viral