Secretions may hold the secret to solve the salmon lice prolem
Researchers in Scotland have found protein differences between larval and adult stages that could help develop vaccines against the parasite
A first-of-its-kind University of Stirling study could better inform strategies to control salmon lice, after researchers uncovered major differences in the secretions the parasite produces as larvae.
Like other parasites, such as mosquitoes and ticks, salmon lice secrete substances from their glands which make it easier for them to feed or evade their host’s immune system.
The study, led by PhD researcher Alexander Dindial alongside colleagues Professor James Bron and Dr Sean Monaghan at Stirling’s Institute of Aquaculture, in collaboration with Kevin McLean of Moredun Research Institute near Edinburgh, compared secretory proteins released by infectious copepodid stage salmon lice (Lepeophtheirus salmonis) with those found in adult lice.
Early infection
They found considerable differences in proteins between the two life stages, which they believe could provide an important insight about successful early infection on susceptible hosts such as Atlantic salmon.
Salmon lice feed on the skin, mucus, and blood of the fish, causing open wounds that can lead to infection – reducing their market value, and increasing the chances of secondary infections and susceptibility to other diseases.
Various treatments have been developed to tackle sea lice infestations in aquaculture but medicinal treatments vary in effectiveness and can impact the environment, and mechanical treatments with wellboats - now the most common delousing method - are expensive and can negatively impact fish welfare if carried out frequently, although mortality has been significantly reduced as techniques have been refined.
143 proteins
In total, 143 secretory proteins were found in copepodid secretions that are absent in adults including many such as serpins, previously identified in land‑based terrestrial ectoparasites, that have been shown to play a role in limiting the host’s immune response.
Lead researcher Alexander Dindial said: “Because this is the very first stage of this parasite’s life cycle, it represents a vital linchpin in control strategies for this species. This work better helps us understand salmon louse biology and could play a vital role in informing future research into control of this parasite, such as through the identification of vaccine targets, which ultimately promote the sustainable production of healthy salmon and enhance global food security.”
The study involved researchers taking samples of larval salmon lice (over 100 copepodids per millilitre of liquid) and incubating them in either filtered seawater or a solution consisting of filtered seawater and isophorone, a chemical naturally found in Atlantic salmon mucus that is known to serve as an attractant for copepodids.
They then concentrated the secretion-containing solutions and analysed the good quality protein present.
Vaccine candidates
A technique called liquid chromatography tandem mass spectrometry was used to analyse the exact protein compositions of each of the samples. This involved the use of a state-of-the-art machine that separates the components of samples, breaks them into fragments, and weighs them - revealing the unique molecular make-up of each protein.
Researchers then filtered the data, identifying the proteins, determining which were secretory in origin, and comparing the compositions of each of the samples.
Dr Sean Monaghan, co-supervisor of the study, said: “This data provides key candidates for vaccines in the future. We are currently exploring the genes of these secreted proteins as part of a large BBSRC (Biotechnology and Biological Sciences Research Council) funded project, GeNoLice, to determine if they are influenced by interactions with the host.”
Investigation of proteins identified in the secretory and excretory products (SEPs) of the infectious copepodid stage of the salmon louse Lepeophtheirus salmonis is published in the journal Veterinary Parasitology.
It was led by the University of Stirling, working in collaboration with the Moredun Research Institute and funded by EastBio, a partnership of educational and research institutions along the East coast of Scotland that aims to deliver world-class interdisciplinary training to bioscience PhD students.
