The interaction of infectious salmon anaemia virus (ISAV) with the blue mussel,Mytilus edulis

Abstract

Integrated multi-trophic aquaculture (IMTA) is an alternative approach to mono-culture aquaculture that reduces environmental impacts of commercial aquaculture systems by combining the cultivation of fed species with extractive species. Shellfish play a critical role in IMTA systems by filter-feeding particulate-bound organic nutrients. They may also increase or decrease disease risk on farms by serving as reservoirs or barriers for important finfish pathogens such as infectious salmon anaemia virus (ISAV). This study aimed to optimize culture and molecular assays in shellfish tissues and to determine the fate of ISAV in mussels, Mytilus edulis. To determine detection limits, qRT-PCR and culture assays in both CHSE-and ASK cells were optimized in ISAV-inoculated mussel tissue homogenates. Both qRT-PCR and culture assays performed in ASK cells had comparable detection limits of 10 2.8 TCID 50 mL À1 . The ISAV RNA genome was consistently detected in digestive gland tissue of ISAVexposed mussels. Viable ISAV was not detected in mussel tissues by culture analysis in CHSE-and ASK cells. The fact that qRT-PCR analysis resulted in positive cycle threshold (CT) values that corresponded to the detectable range of ISAV in ASK culture assays suggests that little to no viable ISAV particles are present in the mussel tissues.

Experimental Transmission of Infectious Pancreatic Necrosis Virus from the Blue Mussel, Mytilus edulis, to Cohabitating Atlantic Salmon (Salmo salar) Smolts

“…The detection limit of the IPNV qRT-PCR assay in fish kidney homogenates was not determined; however, a decrease in sensitivities when performed on mussel digestive gland tissues compared to Atlantic salmon kidney tissues (5,37) was observed for other culture and qRT-PCR assays. This suggests that PCR inhibition in mussel digestive gland tissues is greater than that in fish kidney samples.…”

“…Fish pathogens, including IPNV, are known to persist in the digestive gland (hepatopancreas) tissues of shellfish (7,9). Culture-based and molecular detection of pathogens in mussel digestive gland tissues, however, is difficult due to cell cytotoxicity and PCR inhibitors present in the digestive gland tissues (5). It was therefore important to optimize and determine the detection limits of the assays used to measure viral load in these tissues.…”

“…Mussels are capable of concentrating the bacterial pathogen Vibrio anguillarum and releasing viable pathogen at high concentrations in feces (9). In contrast, the enveloped viral pathogen, infectious salmon anemia virus, and the sea louse, Lepeophtheirus salmonis, are taken up by mussels and inactivated (5,(10)(11)(12). The nonenveloped viral fish pathogen, infectious pancreatic necrosis virus (IPNV), can persist in scallop tissues; however, the fate of IPNV has not yet been determined in mussels (7).…”

“…Bivalves bioaccumulate both viral and bacterial finfish pathogens (5)(6)(7)(8)(9)(10). The physiology of the pathogen influences whether the pathogen remains viable in shellfish tissues and is shed back into the environment.…”

Challenges and emerging technical solutions in on-growing salmon farming

“…However, there may be another positive impact on salmon culture, which also could improve the overall production results. The inclusion within an IMTA system of blue mussels, which can feed on the early life stages of sea lice parasites and other disease organisms (Bartsch et al 2013;Molloy et al 2014) could significantly reduce the disease load on the salmon. In in this way the addition of bivalve culture to the farming system will function as a barrier for parasites passing through the sea cage farm.…”