Grant: Strategic Projects - Group

Considerable debate discusses the interactions of sea lice and wild and farmed salmon in British Columbia. Within this debate, the role of ectoparasitic sea lice in disease propagation (as a vector) or progression (impacts on the host's immunology) has not been described. Many models examine vector-pathogen relationships (e.g., pathogens transmitted by mosquitoes or ticks). However, these models focus on humans or agriculture animals and none exist for a marine ecosystem using fish. Few reports have isolated viral and bacterial pathogens from sea lice, but pathogen transmission has never been tested; thus, the role of sea lice as a vector remains undefined. In other words, when (seasonally) and where (geographically), could sea lice carry important pathogens of salmon? Such information is critical to the salmon farming industry. In a pilot study in British Columbia, Canada, we repeatedly isolated three pathogenic bacterial species from sea lice and their farmed Atlantic salmon hosts. Such results partly support the vector hypothesis but certainly warrant a comprehensive, long-term study. Thus, the proposed research will be conducted in two phases: (1.) we will experimentally test the vector transmission potential of sea lice in a controlled setting to examine their role in disease propagation. (2a.) If transmission occurs, we will analyse seasonal and geographic patterns in pathogen abundance on sea lice from farmed and wild salmonids within an ecological context. Ultimately, we hope to use sea lice as a sentinel species to indicate the presence of pathogens and thereby identify high risk zones. (2b.) If there is no transmission, we will study the effect of sea lice feeding at the microhabitat of the fish's skin. In these experiments, we will test the hypothesis that the feeding activities of lice promote small, localised patches of reduced immune response, thus serving as portals of pathogen entry and replication. This research is topical, yet novel, in that it presents a unique opportunity to study the direct and indirect contribution to disease progression by a commercially important parasite of salmon. It is anticipated that our results will directly assist salmon farmers in the development of effective disease prevention strategies at netpens.