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ARS Home » Northeast Area » Orono, Maine » National Cold Water Marine Aquaculture Center » Research » Research Project #438451

Research Project: Systematic Sampling of Fish and Systems for the Presence of ISAV HPR0

Location: National Cold Water Marine Aquaculture Center

Project Number: 8030-31000-005-018-I
Project Type: Interagency Reimbursable Agreement

Start Date: Jun 1, 2020
End Date: Mar 31, 2022

Infectious salmon anemia virus (ISAV) is a member of the Family Orthomyxoviridae and is the type species for the genus Isavirus. To date all viral isolates that are associated with clinical disease contain a deletion in the highly polymorphic region (HPR) of the gene (segment six) that encodes the haemagglutinin-esterease (HE) protein. These viruses are classified as ISAV HPR-deleted and considered to be pathogenic forms of the virus. Molecular testing has also resulted in the detection of a non-deleted HPR (HPR0) HE gene in fish tissues. To date HPRO virus has never been associated with clinical disease nor isolated in cell culture, thus it is considered a nonpathogenic form of ISAV. However, it is hypothesized that the non-deleted form has the potential to evolve into pathogenic strains of ISAV. This hypothesis resulted in listing of ISAV HPR-deleted and ISAV HPR0 by the World Organization for Animal Health (OIE), and implementation of testing requirements on Atlantic salmon or gamete transfers have been put into place. In an effort to address industry concerns the National Cold Water Marine Aquaculture Center (NCWMAC) began testing gill samples collected from broodstock at spawning. Subsequently, ISAV HPR0 was detected in gill samples collected in November of 2016 and 2017, and again in 2018 and 2019, suggesting that ISAV HPR0 is either being maintained somewhere in the NCWMAC hatchery or is being re-introduced on an annual basis. As the main source of genetics for the Maine industry, failure to determine and mitigate virus entry points at NCWMAC will ultimately impact Atlantic salmon industry growth, production, and trade. Therefore, the immediate objective of this project is to expand current NCWMAC testing to include (1) all life stages of Atlantic salmon held in the hatchery and (2) water, in order to find critical control points that will direct efforts to remove ISAV from the system and preclude its re-entry. The end goal is to prevent future recurrences of ISAV and ensure NCWMAC can deliver eggs from ISAV-free broodstock to maintain robust genetics for the U.S. Atlantic salmon industry.

A systematic monitoring and testing program of animals, incoming water supply, and rearing systems will be developed in collaboration with microbiological and epidemiological experts at Animal and Plant Health Inspection Service (APHIS) and staff at the National Cold Water Marine Aquaculture Center (NCWMAC). The staff of the NCWMAC will then carry out the monitoring and collection of samples. They will arrange for the samples to be tested by a commercial laboratory approved by APHIS. The systematic monitoring and sample plans will include biweekly testing of all incoming water sources over the course of a year, with increased sampling frequency suring periods of elevated concern. Samples of system microbiota will be collected in coordination with water samples. Finally tissue samples from fish within each of the 4 year classes held at the facility will be collected at suspected critical times to look for the presence of the virus at different points in the fishes life history and production cycle.