Serological test performance for bovine tuberculosis in cattle from herds with evidence of on-going infection in Northern Ireland

The ability to accurately identify infected hosts is the cornerstone of effective disease control and eradication programs. In the case of bovine tuberculosis, accurately identifying infected individual animals has been challenging as all available tests exhibit limited discriminatory ability. Here we assess the utility of two serological tests (IDEXX Mycobacterium bovis Ab test and Enfer multiplex antibody assay) and assess their performance relative to skin test (Single Intradermal Comparative Cervical Tuberculin; SICCT), gamma-interferon (IFNγ) and post-mortem results in a Northern Ireland setting. Furthermore, we describe a case-study where one test was used in conjunction with statutory testing. Serological tests using samples taken prior to SICCT disclosed low proportions of animals as test positive (mean 3% positive), despite the cohort having high proportions with positive SICCT test under standard interpretation (121/921; 13%) or IFNγ (365/922; 40%) results. Furthermore, for animals with a post-mortem record (n = 286), there was a high proportion with TB visible lesions (27%) or with laboratory confirmed infection (25%). As a result, apparent sensitivities within this cohort was very low (≤15%), however the tests succeeded in achieving very high specificities (96–100%). During the case-study, 7/670 (1.04%) samples from SICCT negative animals from a large chronically infected herd were serology positive, with a further 17 animals being borderline positive (17/670; 2.54%). Nine of the borderline animals were voluntarily removed, none of which were found to be infected post-mortem (no lesions/bacteriology negative). One serology test negative animal was subsequently found to have lesions at slaughter with M. bovis confirmed in the laboratory.

The ability to accurately identify infected hosts is the cornerstone of effective disease control and eradication programs. In the case of bovine tuberculosis, accurately identifying infected individual animals has been challenging as all available tests exhibit limited discriminatory ability. Here we assess the utility of two serological tests (IDEXX Mycobacterium bovis Ab test and Enfer multiplex antibody assay) and assess their performance relative to skin test (Single Intradermal Comparative Cervical Tuberculin; SICCT), gamma-interferon (IFNg) and post-mortem results in a Northern Ireland setting. Furthermore, we describe a case-study where one test was used in conjunction with statutory testing. Serological tests using samples taken prior to SICCT disclosed low proportions of animals as test positive (mean 3% positive), despite the cohort having high proportions with positive SICCT test under standard interpretation (121/921; 13%) or IFNg (365/922; 40%) results. Furthermore, for animals with a post-mortem record (n=286), there was a high proportion with TB visible lesions (27%) or with laboratory confirmed infection (25%). As a result, apparent sensitivities within this cohort was very low (≤15%), however the tests succeeded in achieving very high specificities (96-100%). During the case-study, 7/670 (1.04%) samples from SICCT negative animals from a large chronically infected herd were serology positive, with a further 17 animals being borderline positive (17/670; 2.54%). Nine of the borderline animals were voluntarily removed, none of which were found to be infected post-mortem (no lesions/bacteriology negative). One serology test negative animal was subsequently found to have lesions at slaughter with M. bovis confirmed in the laboratory.   manufacturer's instructions as follows: an S/P ratio greater or equal to 0.30 was considered 149 positive and a ratio less than 0.3 was negative.

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The Enfer provisioned antibody assay 151 An Enfer provisioned assay was carried out by Enfer staff at their Naas laboratories (Enfer 152 ltd, Naas, Co Kildare). All tests were blinded, with no information on the epidemiological 153 situation (e.g. within-herd prevalence) from which animals were selected provided to Enfer.

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It should be noted that this Enfer multiplex antibody assay is not a commercially available as  confirmation. In addition, we used a combination of IFN, SICCT, VL and culture 204 confirmation, to assess the relative performance of the serology tests.

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The relationship between the test status and the independent variables was modelled throughout 206 using binary logit regression models. A random effect for herd id (to account for potential 207 clustering effects) was included if significant and was tested using a likelihood ratio test. We 208 used χ 2 tests and binary logit models to assess whether there was any association between All data was provided through the APHIS dataset, for which the data controller is DAERA.

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All data from which inferences were made are provided within the paper, raw test data has 235 been deposited in an online repository (25). Additional information on these data is available 236 from DAERA, Northern Ireland (https://www.daera-ni.gov.uk/access-information-0; 237 daera.informationmanager@daera-ni.gov.uk) and would be subject to appropriate GDPR and

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There was a lack of evidence in support for an association between sex on the probability of

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In the current study, a small proportion of animals were disclosed as serology positive (mean 348 3% positive). However, during another study in Northern Ireland, we found a higher 349 proportion of animals were disclosed as positive when prevalence was higher (86% SICCT 350 test reactors) and testing occurred after skin testing (14). The proportion serology positive in       SICCT or IFN -0/6 0/6 0/6 (% serology positive) 0% 0% 0%