Field evaluation of diagnostic sensitivity (DSe) and specificity (DSp) of common tests for amoebic gill disease (AGD) and complex gill disease (CGD) in cultured Atlantic salmon (Salmo salar) in Scotland using Bayesian latent class models

• Published in: Preventive Veterinary Medicine
• Main Authors: Boerlage, AS, Ashby, Angela, Eze, JI, Gunn, GJ, Reeves, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: Gross gill score; Histopathology; Latent class models; Marine gill diseases; Sensitivity; Specificity; /dk/atira/pure/sustainabledevelopmentgoals/life_below_water; name=SDG 14 - Life Below Water; Atlantic salmon; Salmo salar
• Online Access: https://pure.sruc.ac.uk/en/publications/4155a6d2-6e95-405d-ae81-9a374b036336; https://doi.org/10.1016/j.prevetmed.2022.105654; https://pure.sruc.ac.uk/ws/files/46772553/1_s2.0_S0167587722000873_main.pdf; http://www.scopus.com/inward/record.url?scp=85131345130&partnerID=8YFLogxK

Amoebic gill disease (AGD) and complex gill disease (CGD) are the most significant marine gill diseases in salmon aquaculture in Scotland. Little is published about diagnostic performance of tests to detect these diseases, making it difficult to interpret test results. We estimated diagnostic sensitivity (DSe) and specificity (DSp) of common tests for AGD (gross AGD score, qPCR for Neoparamoeba perurans, histopathology) and CGD (gross proliferative gill disease (PGD) score, gross total gill score, histopathology). Because specifications in our sampling protocol implemented to encourage consistency across the farms might affect diagnostic performance of histopathology (historically the reference standard for gill diseases), we used Bayesian latent class models without reference standard. Cases and non-cases were based on less, medium, and severe stringent case definitions, representing different cut-off levels for the different tests. Gross gill scores for both diseases were excellent in designating non-diseased fish, DSps were generally around 1. To detect CGD, DSe of gross total gill score and gross PGD score were between respectively 0.81 (0.73 – 0.91 lower to upper 95% credible interval) and 0.53 (0.46 – 0.64) for medium stringent case definitions, and to detect AGD the DSe for the gross AGD score was between 0.53 (0.48–0.57) and 0.14 (0.07 – 0.22) for respectively the less and severe stringent case definition. Thus, gross gill scores were medium to good in designating truly diseased fish, implying some false negatives are expected. For CGD the DSe for gross total gill scores were the highest, for AGD it was the qPCR test at a DSe of 0.92 (0.86 – 0.99). For both diseases, DSe was lowest for histopathology, e.g. 0.23 (0.16 – 0.30) for AGD and 0.1 (0.07 – 0.14) for CGD under medium stringent case definitions, perhaps due to collecting the second gill arch on the right rather than the worst affected arch, whilst PCR sampling and gross gill scoring included multiple (PCR) or all (gross scoring) gill arches. The ...