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Title: Increased susceptibility to infectious salmon anemia virus (ISAv) in Lepeophtheirus salmonis – infected Atlantic salmon

item BARKER, SARAH - University Of Maine
item COVELLO, JENNIFER - Atlantic Veterinary College
item BOUCHARD, DEBBIE - University Of Maine
item Wolters, William
item PRUCELL, SARA - Atlantic Veterinary College
item FAST, MARK - Atlantic Veterinary College
item BRICKNELL, IAN - University Of Maine

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 6/10/2014
Publication Date: 8/14/2014
Citation: Barker, S., Covello, J., Bouchard, D., Wolters, W.R., Prucell, S., Fast, M., Bricknell, I. 2014. Increased susceptibility to infectious salmon anemia virus (ISAv) in Lepeophtheirus salmonis – infected Atlantic salmon. [Abstract]. Th 10th International Sea Lice Conference, Portland, Maine, U.S.A. 1:1.

Interpretive Summary:

Technical Abstract: The salmon louse and infectious salmon anemia virus (ISAv) are the two most significant pathogens of concern to the Atlantic salmon (Salmo salar) aquaculture industry. However, the interactions between sea lice and ISAv, as well as the impact of a prior sea lice infection on the susceptibility of the host to ISAv are still poorly understood. Therefore, this project aimed to determine a) whether sea lice take ISAv up from infected hosts, b) do sea lice remain infectious following host re-assortment, and c) are Atlantic salmon infected with sea lice more susceptible to ISAv and the impact(s) on their ability to respond to ISAv infection. The data show that L. salmonis do appear to ‘take up’ viable ISAv when feeding on / infecting an ISAv positive Atlantic salmon host. L. salmonis were found to be positive for detectable viable ISAv at 16, 37 and 51 days post-exposure of the host fish to ISAv via a cohabitation challenge. They were found to be positive for viable ISAv up to four hours post-removal from the fish. Adult L. salmonis also appear capable of transmitting viable ISAv from an ISAv-infected Atlantic salmon to a naïve Atlantic salmon. When ISAv naïve salmon were infected with four adult lice per fish that had been removed from an ISAv-infected fish, 36.7% of naïve fish, were found to be positive for viable ISAv 30 days post-exposure (d.p.e.). Finally, salmon pre-infected with late chalimus and pre-adult L. salmonis prior to ISAv exposure appear more susceptible to ISAv infection. Viable ISAv was detected earlier in cohabitee fish with a prior lice infection at 16 d.p.e. to ISAv compared to 37 d.p.e. to ISAv in the cohabitee fish without sea lice, and significantly lower survival was observed. Previous infection with sea lice appears to have some negative effects on the ability of Atlantic salmon to mount an appropriate early immune response to subsequent ISAv exposure, which will be discussed further. It is hypothesized that this may be due to the fact that the immune response is already geared towards responding to the sea lice infection, potentially leading to delayed viral recognition and activation of an appropriate early immune response to ISAv.