Developing tools for the characterisation of host-pathogen interactions in amoebic gill disease (AGD) of Atlantic salmon (Salmo salar)

Abstract

Atlantic salmon production (Salmo salar) has increased in-line with global population growth and changes in consumption patterns, causing the emergence of several infectious diseases. Gill disorders, such as amoebic gill disease (AGD), have posed a particular problem. Thus, limiting the levels of infection by its causative agent, Neoparamoeba perurans, is considered to be one of the main challenges for salmon producers worldwide. Current treatments often lead to re-infection and may eventually cause indirect and direct economic losses. Hence, the development of alternative treatments is required. Therefore, this study focused on the search and development of tools for the characterisation of host-pathogen interactions between Atlantic salmon and N. perurans. Firstly, an improved quantification of amoebae was accomplished through the comparison of different swab materials and the swabbing of different gill arches, showing a potential advantage by sampling the 4th gill arch and by using alginate-fibre tipped swabs in contrast to the other gill arches and swab materials. Additionally, the study of a better in-situ method for the preservation of mucus was explored through the use of a range of fixatives. Methacarn solution provided significantly greater retention of the mucus covering of the gill epithelium while aiding the preservation of amoeba trophozoites embedded in the mucus. In addition, the potential effect of the commonly applied hydrogen peroxide (H2O2) treatment was assessed through use of a range of molecular tools to examine the gills of H2O2-treated fish and of AGD-infected fish. Results suggested evidence of a T-cell response after treatment, while a possible immunomodulation by the parasite was found in the AGD-infected fish. Lastly, the in-silico screening and identification of potential vaccine candidates within the N. perurans transcriptome provided a final list of cell membrane proteins, enzymes and structural proteins which could potentially serve as ideal candidates for vaccine development.