A systematic surveillance programme for infectious salmon anaemia virus supports its absence in the Pacific Northwest of the United States

Abstract

In response to reported findings of infectious salmon anaemia virus (ISAV) in British Columbia (BC), Canada, in 2011, U.S. national, state and tribal fisheries managers and fish health specialists developed and implemented a collaborative ISAV surveillance plan for the Pacific Northwest region of the United States. Accordingly, over a 3-1/2-year period, 4,962 salmonids were sampled and successfully tested by real-time reverse-transcription PCR. The sample set included multiple tissues from free-ranging Pacific salmonids from coastal regions of Alaska and Washington and farmed Atlantic salmon (Salmo salar L.) from Washington, all representing fish exposed to marine environments. The survey design targeted physiologically compromised or moribund animals more vulnerable to infection as well as species considered susceptible to ISAV. Samples were handled with a documented chain of custody and testing protocols, and criteria for interpretation of test results were defined in advance. All 4,962 completed tests were negative for ISAV RNA. Results of this surveillance effort provide sound evidence to support the absence of ISAV in represented populations of free-ranging and marine-farmed salmonids on the northwest coast of the United States.

Molecular testing of adult Pacific salmon and trout (Oncorhynchus spp.) for several RNA viruses demonstrates widespread distribution of piscine orthoreovirus in Alaska and Washington

“…Fish sampling was conducted as described in the companion paper reporting the results of the U.S. surveillance plan (Gustafson et al., ). Briefly, adult salmon and anadromous trout were sampled over two spawning periods: study year 1 included adults returning in 2012–2013 and study year 2 included adults returning in 2013–2014 (Tables S1 and S2).…”

“…All surveillance samples were first screened for ISAV using the method approved by the U.S. Department of Agriculture—Animal and Plant Health Inspection Service (USDA‐APHIS) National Veterinary Services Laboratory (NVSL). All samples tested negative for ISAV RNA using the approved method (Gustafson et al., ). Once a sample was confirmed negative, the duplicate frozen tissue samples (WA samples) or the remaining frozen samples (AK samples) were submitted directly to the U.S. Geological Survey—Western Fisheries Research Center (WFRC) by the collecting agency for use in the present study.…”

“…Once a sample was confirmed negative, the duplicate frozen tissue samples (WA samples) or the remaining frozen samples (AK samples) were submitted directly to the U.S. Geological Survey—Western Fisheries Research Center (WFRC) by the collecting agency for use in the present study. While the companion surveillance study examined 4,962 fish for ISAV RNA (Gustafson et al., ), we conducted expanded testing on a randomly selected set of stock cohorts that included only 2,252 fish (45% of the total samples).…”

“…In response to the initial reports of ISAV in BC, the United States Congress directed the National Aquatic Animal Task Force to address the significance of these findings for native free‐ranging species of Pacific salmon and trout (Amos et al., ). As described in the accompanying paper (Gustafson et al., ), the U.S. response included a systematic ISAV surveillance effort in WA and AK with the primary screening conducted using an OIE‐recommended universal real‐time, reverse transcription PCR (rRT‐PCR) assay targeting segment 8 of the ISAV genome (Snow et al., ).…”

A molecular assessment of infectious agents carried by Atlantic salmon at sea and in three eastern Canadian rivers, including aquaculture escapees and North American and European origin wild stocks

“…The virus has been observed in wild and cultured salmon in eastern Canada and the USA (Bouchard et al 1999(Bouchard et al 2001Ritchie et al 2001;Olivier 2002) and detected at low prevalence (<1%) in escaped aquaculture fish in Norway (Madhun et al 2017). In wild fish, most if not all detections have shown no evidence of disease (including challenged hosts); therefore, it is assumed to be the avirulent HRP0 strain that is affecting asymptomatic wild hosts (Plarre et al 2005;Gustafson et al 2018). It is not known whether wild fish have been affected by virulent strains of ISAV, which can develop spontaneously from the avirulent strain through a deletion in segment 6 (Nylund et al 2003;Godoy et al 2013).…”