Infectious salmon anaemia virus aquaculture: emergence of low pathogenic ISAV-HPR0 and re-emergence of virulent ISAV-HPR[DELA]: HPR3 and HPR14

• Published in: Virology journal Vol. 10
• Main Authors: Godoy, Marcos G, Kibenge, Molly JT, Suarez, Rudy, Lazo, Eduardo, Heisinger, Alejandro, Aguinaga, Javier, Bravo, Diego, Mendoza, Julio, Llegues, Katerina O, Avendaéo-Herrera, Rubñn, Vera, Cristian, Mardones, Fernando, Kibenge, Frederick SB
• Format: Journal Article
• Language: English
• Published: BioMed Central Ltd 23-11-2013
• Subjects: Analysis; Anemia; Atlantic salmon; Care and treatment; Genetic aspects; Phylogeny; Risk factors; Salmon; Virulence (Microbiology); Virus diseases
• ISSN: 1743-422X; 1743-422X
• DOI: 10.1186/1743-422X-10-344

Abstact 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[DELA]). This study shows the historic dynamics of ISAV-HPR[DELA] and ISAV-HPR0 in Chile, the genetic relationship among ISAV-HPR0 reported worldwide and between ISAV-HPR0 and ISAV-HPR[DELA] 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[DELA] 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 (.sup.360PST.sup.362, .sup.360PAN.sup.362 and .sup.360PAT.sup.362) in HPR. The virus responsible for the 2013 ISAV-HPR[DELA] 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 .sup.360PAT.sup.362, which is the only type of ISAV-HPR0 variant found in Chile. This suggested to us that the 2013 ISAV-HPR[DELA] re-emerged from ISAV-HPR0 that is enzootic in Chilean salmon aquaculture and were not new introductions of virulent ISAV-HPR[DELA] 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[DELA] viruses and the possibility that it could mutate to virulent ISAV-HPR[DELA]. Keywords: Low pathogenic infectious salmon anaemia virus, ISAV-HPR0, Virulent ISAV, ISAV-HPR[DELA], Virulence, Salmo salar