DAO 65:9-16 (2005)  -  doi:10.3354/dao065009

Validation of in situ hybridisation and histology assays for the detection of the oyster parasite Marteilia refringens

A. Thébault1, S. Bergman2, R. Pouillot1, F. Le Roux3, F. C. J. Berthe4,*

1Agence Française de Sécurité Sanitaire des Aliments – La Direction de l‘Évaluation des Risques Nutritionnels etSanitares (AFSSA-DERNS), Unité d'Appui Epidémiologique à l'Analyse du Risque, 27-31 Avenue du Général Leclerc, BP 19, 94701 Maisons-Alfort, France
2Federal Research Centre for Virus Diseases of Animals, National Reference Laboratory for Mussel Diseases,Boddenblick 5 a, 17498 Insel Riems, Germany
3Ifremer, Laboratoire de Génétique et Pathologie, Community Reference Laboratory for Mollusc Diseases, Reference Laboratory for Bonamiosis and Marteiliosis, BP 133, 17390 La Tremblade, France
4Department of Pathology & Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Ave., Charlottetown, Prince Edward Island C1A 4P3, Canada
*Corresponding author. Email: fberthe@upei.ca

ABSTRACT: An in situ hybridisation technique has been developed for the detection of infection in oysters with Marteilia refringens with particular emphasis on light infections or confirmation of suspected cases by means of histology. Although validation of new diagnostic methods is usually achieved by comparison with standard techniques, in our case the sensitivity and specificity of the standard (histology) had not previously been established. Another point to consider is that surveillance and monitoring frequently target populations displaying different levels of prevalence under different field conditions. The objective of our study was to evaluate the sensitivity and specificity values of in situ hybridisation and histology for the detection of M. refringens, based on 3 populations of flat oysters, free of the disease and with mild and high levels of prevalence. A blind assay of 200 individuals from each population was performed using both techniques. Results were analysed by means of the classical approach and latent models (maximum likehood and Bayesian approach). Assumptions and results were found to vary slightly with the different statistical approaches. The more realistic estimate by the Bayesian approach shows a link between the level of prevalence and the sensitivity of the techniques. Values of sensitivity and specificity for histology were 0.7 and 0.99 respectively, and 0.9 and 0.99 respectively in the case of in situ hybridisation. Some uncertainty remains regarding these values because the study does not take into account the severity of infection or the developmental stages of the parasite actually present in each individual. This work provides valuable information with regard to the choice and potential use of those 2 diagnostic methods currently recommended by international standards.

KEY WORDS: Diagnostic · Validation · Sensitivity · Specificity · Latent models · Marteilia refringens · Ostrea edulis

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