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Peredikksyre som behandling av amøbegjellesykdom (AGD) i laks (PERAGILL) / Peracetic acid as a potential treatment for amoebic gill disease (AGD) in Atlantic salmon

AGD is a significant health and disease problem in Atlantic salmon aquaculture. Since the first documented case of AGD in Norway, the threats have been quite persistent and the number of reported cases is showing an upward trajectory trend. The industry must be kept abreast with sustainable treatment options to combat this emerging threat. The use of freshwater and oxidative disinfectant bathing are the two strategies being applied in commercial production. Peracetic acid (PAA), an organic peroxide, is being considered as a more sustainable disinfectant in aquaculture compared with other conventional disinfectants. PAA offers some advantages that may address the challenges in the currently available treatments for AGD. Given the escalating threat that AGD is posing to the Norwegian salmon aquaculture industry, there is indeed a big challenge to develop alternative methods that have the potential in addressing issues on efficacy, practicality and most importantly, sustainability. The documented features of PAA make it a good candidate to be explored as a treatment for AGD. The exploration of this potential must be provided with a complementary toolbox that will assess treatment impacts and success through insights from different biological perspectives.

Main objective
To explore the potential of peracetic acid (PAA) as an alternative and sustainable treatment to amoebic gill disease.
Sub-objectives STAGE I (Funded 2017–2019)
• To investigate the amoebicidal activity of PAA and identify influencing factors (work package 1).
• To assess the impact of PAA treatment on fish health and welfare (WP1).
• To determine the potential environmental risk of PAA treatment (WP2).
• To develop integrative assessment toolbox to evaluate treatment impacts and efficacy (WP3).
Sub-objectives STAGE II (Provided funding from 2019)
• To characterise the different factors affecting the dynamics of PAA treatment in AGD-infected fish (WP4).
• To compare conventional AGD treatments with PAA application (WP5).
Expected project outcome
The project will attempt to offer the salmon aquaculture industry an effective and eco-friendly therapeutic measure for AGD. The expected results will provide the industry significant long-term benefits because a new alternative solution to an existing problem is to be developed, especially that it may offer practical advantages in cases where the current treatments for AGD are hampered with logistical concerns. Lastly, fundamental knowledge will be generated, such as the identification of markers for treatment assessment that may be utilised in future endeavors, especially in the development of diagnostic tools and therapeutics for AGD.
Project design and implementation
The project is organised into five work packages (WPs). 
WPs 1–3 constitute activities for STAGE I, which are funded from 2017–2019.
Depending on the outcomes of STAGE I, further funding of WPs 4–5 (STAGE II) will be considered.
WP1 is the backbone of the project and together with WP2, will lay the foundation for WPs 4–5. WP1 will explore the effects of PAA on the causative agent and on the host. WP2 will evaluate the environmental risk associated with PAA treatment. WP4 will investigate different PAA application strategies to treat AGD infection. WP5 will compare the efficacy of PAA with the two conventional AGD treatments. WP3 constitutes the toolbox that will be used to assess the effects and efficacy of the treatment and will bridge STAGES I and II.
STAGE I (funded 2017–2019)
WP1 – Amoebicidal activity and health-related impacts
This WP will explore the amoebicidal activity of different peracetic acid based disinfectants against several Norwegian isolates of N. perurans. Several factors will be tested to understand the susceptibility of the amoeba and the mechanisms of actions of PAA. The health-related impacts of PAA exposure will likewise be investigated.
WP2 – Environmental impacts 
Based on literature review and PAA residual measurements in seawater exposure trials, degradation time (DT50) and half-lives of PAA will be identified. Degradation products will be quantified and the levels will be compared with existing data concerning safe limits in Norwegian setting. The work package will also include recommendations for solutions to minimise discharge of PAA residuals under different treatment scenarios.
WP 3 – Integrative assessment toolbox
WP3 will provide the tools and techniques to assess the effects and the efficacy of PAA treatments. The integration of traditional and modern approaches and tools would facilitate the development of a toolbox that will be valuable in future research concerning AGD treatments, especially with the use of oxidative disinfectants. At the end of the project, the predictive nature of the tools will be assessed.
STAGE II (provided funding from 2019)
WP4 – Treatment of AGD-infected salmon
AGD will be experimentally induced in salmon using an established AGD challenge model. PAA treatment will be performed either during the early or later stage of infection. Several factors that are expected to influence the efficacy of treatment will be investigated, such as temperature, duration of exposure, time of treatment and stress status of fish. The potential risk to develop resistance against PAA will be explored in this work package.
WP 5 – Comparative study of different AGD treatments
This work package will compare PAA application with two of the existing AGD treatments, i.e., freshwater and H2O2 bathing. Treatment protocol for PAA identified in WP4 will be employed in the comparative study. 
Project organization
Nofima will lead the project and will carry out most of the experimental works involved. DTU Aqua will carry out part of WP1 and will lead WP2. Quantidoc AS will perform the histological examination of all samples collected. Lilleborg AS will provide all the disinfectants that will be used in the experiment.

Dissemination of project results
The results of the study will be made available through print and online communication channels. All peer-reviewed publications will be distributed under Open Access scheme. Popular science articles, both in Norwegian and English, will be published in communication media that are highly relevant to the industry. The dissemination and communication channels of Nofima and of the partner institutions will be maximised.

The results are expected to be presented at national and international conferences/symposia as poster and/or oral presentations. Conferences organised by FHF and the Research Council of Norway (e.g., Havbruk and Friskfisk) are excellent opportunities to establish the credential of the project at a national level. At the international scene, conferences with close connection with the industry (i.e., Aquaculture Europe, World Aquaculture) are priorities for result dissemination.