Improved 18S rDNA profiling of parasite communities in salmonid tissues using a host blocking primer

Sensitive screening of eukaryotic communities in aquaculture for research and management is limited by the availability of technologies that can detect invading pathogens in an unbiased manner. Amplicon sequencing of 18S ribosomal DNA (rDNA) provides a potential pan-diagnostic test to overcome these biases; however, this technique is limited by a swamping effect of host DNA on low abundance parasite DNA. In this study, we have adapted a host 18S rDNA blocking assay to amplify eukaryotic DNA from salmonid tissue for amplicon sequencing. We demonstrate that effective salmonid 18S rDNA blocking enables sensitive detection of parasite genera in salmonid gill swabs. Furthermore, 18S rDNA amplicon sequencing with host blocking identified enriched pathogen communities in gill swabs from Atlantic salmon suffering from severe clinical gill infections compared to those exhibiting no clinical signs of gill infection. Application of host 18S rDNA blocking in salmonid samples led to improved detection of the amoebic parasite Neoparamoeba perurans, a parasite of significant threat to the Atlantic salmon aquaculture industry. These results reveal host 18S rDNA blocking as an effective strategy to improve the profiling and detection of parasitic communities in aquaculture species. This assay can be readily adapted to any animal species for improved eukaryotic profiling across agricultural and veterinary industries.