Mucosal health and microbiota during sea lice parasitism: effect of oral delivery of immunomodulants

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The mucosal surfaces (skin, intestine and gills) of fish are constantly interacting with a wide range of pathogens and, in concert with the resident mucosal microbiota, are the first line of host defence. Several immune factors have been described in fish mucus and their presence and abundance can be affected by pathogen infection. As a consequence, the mucosa-associated microbiota can be affected and this may lead to dysbiosis, a microbial imbalance on or inside the body, which reduces the beneficial role of microbiota on the innate immune system and may lead to secondary infections by opportunistic microbes. Sea lice (Lepeophtheirus salmonis and Caligus spp.) infections are the most economically important causative agents of disease in marine-farmed salmonids worldwide. Caligus rogercresseyi is the main ectoparasite affecting the Chilean salmon industry with estimated costs of up to $120 million annually. This parasite damages external surfaces of the integument providing portal of entry for secondary infectious pathogens, and infected fish also become stressed which leads to immunosuppression with consequent increased susceptibility to the secondary infections. Other Caligid parasites (Caligus rogercresseyi and other Caligus spp.) have detrimental impacts on mariculture operations in both developing and developed parts of the world which causes economic losses of US$ 100's millions annually. The development of novel methods to prevent or reduce sea lice infection is therefore a high priority for the industry. An essential prerequisite for improved treatments strategies is a better understanding of relationship between host-microbiome-parasite at the epidermal interface. Therefore, the aim of this research programme is to evaluate the influence of sea lice parasitism on mucosal health, including aspects of the immune response and host microbiota. We will evaluate the effect of immunomodulants on susceptibility to sea lice infection, and on gut and mucus quality by determining epidermal mucus proteomic responses, microbiota changes and mucosal transcriptomic changes. We will correlate the responses of the host and the sea lice during the early stages of parasitism in order to develop new strategies (i.e. identify antigens for vaccines, targets for RNAi, probiotics, prebiotics, immunomodulants) for sea ice control.