Contents lists available at ScienceDirect Preventive Veterinary Medicine journal homepage: www.elsevier.com/locate/prevetmed Accuracy of PCR, mycobacterial culture and interferon-γ assays for detection of Mycobacterium bovis in blood and milk samples from Egyptian dairy cows using Bayesian modelling Ibrahim Elsohaby a,b, *, Yasser S. Mahmmod a,c , Marshal M. Mweu d , Heba A. Ahmed e , Mohamed M. El-Diasty f , Attia A. Elgedawy g , Eman Mahrous g , Fatma I. El Hofy h a Department of Animal Medicine, Division of Infectious Diseases, Faculty of Veterinary Medicine, Zagazig University, Egypt b Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Canada c Section of Veterinary Sciences, Health Sciences Division, Al Ain Men’s College, Higher Colleges of Technology, United Arab Emirates d School of Public Health, College of Health Sciences, University of Nairobi, Nairobi, Kenya e Department of Zoonoses, Faculty of Veterinary Medicine, Zagazig University, Egypt f Animal Health Research Institute, Mansoura Provincial Lab., Egypt g Animal Health Research Institute, Dokki, 12618, Giza, Egypt h Department of Bacteriology, Immunology and Mycology, Faculty of Veterinary Medicine, Benha University, Egypt ARTICLE INFO Keywords: Bovine tuberculosis Dairy cows Sensitivity and specificity Bayesian modelling PCR Interferon-γ Mycobacterial culture ABSTRACT The number of bovine tuberculosis (bTB) infected dairy herds in Egypt is growing and this calls for accurate and reliable diagnostic methods at cow level for cost-effective bTB eradication as culling of the whole herd is not economically sustainable. The present study aimed to estimate the sensitivity (Se) and specificity (Sp) of PCR, mycobacterial culture and interferon-γ (IFN-γ) assays for Mycobacterium bovis (M. bovis) detection in blood and milk samples from dairy cows in Egyptian dairy herds within a Bayesian framework. As a secondary objective, the distribution of true within-herd prevalence of M. bovis infection was estimated. Blood and milk samples were collected from 245 Holstein dairy cows in 11 Egyptian dairy herds and subjected to PCR, mycobacterial culture and IFN-γ testing. With respect to the detection of M. bovis in blood, IFN-γ recorded higher Se [0.97 (95% Posterior Credible Interval (PCI): 0.87–1.00)] than PCR [0.68 (95% PCI: 0.53–0.95)] and culture [0.22 (95% PCI: 0.13–0.37)]. However, Sp estimates of PCR [0.98 (95% PCI: 0.95–1.00)], culture [0.99 (95% PCI: 0.98–1.00)] and IFN-γ [0.97 (95% PCI: 0.88–1.00)] were comparable. As for milk samples, Se estimate of PCR [0.29 (95% PCI: 0.01–0.60)] was higher than that of culture [0.08 (95% PCI: 0.001–0.23)]. However, the Sp estimates of both tests were statistically similar. The estimated true within-herd prevalences of M. bovis varied across the tested bovine subpopulations and ranged between 0.06 and 0.66. In conclusion, IFN-γ registered a similar overall performance to PCR but was superior to mycobacterial culture. With its good accuracy and wide applicability, IFN-γ lends itself to use in the Egyptian bTB eradication program. 1. Introduction Bovine tuberculosis (bTB) is a chronic zoonotic disease caused by Mycobacterium bovis (M. bovis)(Michel et al., 2010). Cattle are the primary hosts for M. bovis and infected cattle remain subclinical for a long time until clinical symptoms of bTB exhibited (Allen et al., 2010). M. bovis is globally distributed and has significant implications on an- imal and human health and international trade (Collins, 2006; Zinsstag et al., 2006; Good et al., 2011). Therefore, accurate, reliable and cost- effective diagnostics are essential for effective detection and subsequent eradication of bTB from cattle populations (de la Rua-Domenech et al., 2006; Pucken et al., 2017). Currently, several diagnostic tools are available for M. bovis infec- tion detection in cattle. These tools can be broadly categorized into direct (targeting the bacterium or its debris) and indirect (measuring the host’s immune response to infection) tests. The single intradermal tuberculin test is the most commonly used indirect method for early detection of cattle infected with M. bovis (Monaghan et al., 1994). It https://doi.org/10.1016/j.prevetmed.2020.105054 Received 28 March 2020; Received in revised form 5 June 2020; Accepted 5 June 2020 ⁎ Corresponding author at: Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, C1A 4P3, Canada. E-mail address: ielsohaby@upei.ca (I. Elsohaby). Preventive Veterinary Medicine 181 (2020) 105054 0167-5877/ © 2020 Elsevier B.V. All rights reserved. T