Estimation of the Relative Sensitivity of the Comparative Tuberculin Skin Test in Tuberculous Cattle Herds Subjected to Depopulation

Katerina Karolemeas,Andrew P Mitchell,Richard S Clifton-Hadley,Andrew J K Conlan,Roderick Cooper,Anthony V Goodchild,James L N Wood,R Glyn Hewinson,Trevelyan J Mckinley,Ricardo De La Rua-Domenech,Christl A Donnelly,Lionel G Filion

doi:10.1371/journal.pone.0043217

Katerina Karolemeas, Andrew P Mitchell + Show 10 more

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https://doi.org/10.1371/journal.pone.0043217

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Abstract

Bovine tuberculosis (bTB) is one of the most serious economic animal health problems affecting the cattle industry in Great Britain (GB), with incidence in cattle herds increasing since the mid-1980s. The single intradermal comparative cervical tuberculin (SICCT) test is the primary screening test in the bTB surveillance and control programme in GB and Ireland. The sensitivity (ability to detect infected cattle) of this test is central to the efficacy of the current testing regime, but most previous studies that have estimated test sensitivity (relative to the number of slaughtered cattle with visible lesions [VL] and/or positive culture results) lacked post-mortem data for SICCT test-negative cattle. The slaughter of entire herds (“whole herd slaughters” or “depopulations”) that are infected by bTB are occasionally conducted in GB as a last-resort control measure to resolve intractable bTB herd breakdowns. These provide additional post-mortem data for SICCT test-negative cattle, allowing a rare opportunity to calculate the animal-level sensitivity of the test relative to the total number of SICCT test-positive and negative VL animals identified post-mortem (rSe). In this study, data were analysed from 16 whole herd slaughters (748 SICCT test-positive and 1031 SICCT test-negative cattle) conducted in GB between 1988 and 2010, using a Bayesian hierarchical model. The overall rSe estimate of the SICCT test at the severe interpretation was 85% (95% credible interval [CI]: 78–91%), and at standard interpretation was 81% (95% CI: 70–89%). These estimates are more robust than those previously reported in GB due to inclusion of post-mortem data from SICCT test-negative cattle.

Highlights

Bovine tuberculosis, caused by Mycobacterium bovis, is a zoonotic disease that is endemic in many countries worldwide, impacting on animal health, welfare, productivity and trade
These animals, which represented between 1 and 8% of the number of animals slaughtered in each herd respectively, were excluded from the relative SICCT test sensitivity (rSe) calculations, as described in the Materials and Methods section
The results suggest that even with the increased sensitivity at the more severe interpretation, undetected infected cattle may remain in some breakdown herds that are officially released from movement restrictions

Summary

Introduction

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is a zoonotic disease that is endemic in many countries worldwide, impacting on animal health, welfare, productivity and trade. The intradermal tuberculin test is recognised by the World Organisation for Animal Health (OIE) and the European Commission as the primary screening test for detection of bTB in cattle [3,4]. The application of this test, supplemented with slaughterhouse surveillance and movement controls on infected and suspect herds, underpins many bTB control programmes worldwide and, in the absence of wildlife reservoirs for M. bovis, has led to the successful eradication of bTB in many countries [4,5,6]

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