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

• Main Authors: Godoy, Marcos G, Kibenge, Molly JT, Suarez, Rudy, Lazo, Eduardo, Heisinger, Alejandro, Aguinaga, Javier, Bravo, Diego, Mendoza, Julio, Llegues, Katerina O, Avendaño-Herrera, Rubén, Vera, Cristian, Mardones, Fernando, Kibenge, Frederick SB
• Format: Other/Unknown Material
• Language: English
• Published: BioMed Central Ltd. 2013
• Subjects: Low pathogenic infectious salmon anaemia virus; ISAV-HPR0; Virulent ISAV; ISAV-HPR∆; Virulence; Salmo salar; Atlantic salmon
• Online Access: http://www.virologyj.com/content/10/1/344

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∆). 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 ( 360 PST 362 , 360 PAN 362 and 360 PAT 362 ) 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 360 PAT 362 , 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∆.