Bayesian Receiver Operating Characteristic Estimation of Multiple Tests for Diagnosis of Bovine Tuberculosis in Chadian Cattle

Abstract

BackgroundBovine tuberculosis (BTB) today primarily affects developing countries. In Africa, the disease is present essentially on the whole continent; however, little accurate information on its distribution and prevalence is available. Also, attempts to evaluate diagnostic tests for BTB in naturally infected cattle are scarce and mostly complicated by the absence of knowledge of the true disease status of the tested animals. However, diagnostic test evaluation in a given setting is a prerequisite for the implementation of local surveillance schemes and control measures.Methodology/Principal FindingsWe subjected a slaughterhouse population of 954 Chadian cattle to single intra-dermal comparative cervical tuberculin (SICCT) testing and two recently developed fluorescence polarization assays (FPA). Using a Bayesian modeling approach we computed the receiver operating characteristic (ROC) curve of each diagnostic test, the true disease prevalence in the sampled population and the disease status of all sampled animals in the absence of knowledge of the true disease status of the sampled animals. In our Chadian setting, SICCT performed better if the cut-off for positive test interpretation was lowered from >4 mm (OIE standard cut-off) to >2 mm. Using this cut-off, SICCT showed a sensitivity and specificity of 66% and 89%, respectively. Both FPA tests showed sensitivities below 50% but specificities above 90%. The true disease prevalence was estimated at 8%. Altogether, 11% of the sampled animals showed gross visible tuberculous lesions. However, modeling of the BTB disease status of the sampled animals indicated that 72% of the suspected tuberculosis lesions detected during standard meat inspections were due to other pathogens than Mycobacterium bovis.Conclusions/SignificanceOur results have important implications for BTB diagnosis in a high incidence sub-Saharan African setting and demonstrate the practicability of our Bayesian approach for diagnostic test evaluation.

Association between microsatellite markers and bovine tuberculosis in Chadian Zebu cattle

“…The BTB incidence estimates in the present study were higher than previously reported in the original dataset (954 animals) by [15,16]. This may be due to the difference in the number of animals tested in the original dataset and our subsample dataset.…”

“…A total of 251 animals were sampled during three intervals of approximately one month between July and November 2005 at abattoirs in Southern Chad, approximately 500 km from N'Djamena, the capital of Chad. Details of the resource population can be found in [15,16]. Briefly, animals belonged to two indigenous cattle breeds known as "Arab" and "Mbororo" of zebu origin.…”

“…Under the BM estimate, animals were designated either non-diseased = 0 or diseased = 1. A detailed BM and the mathematical description are provided in [15]. …”

The Accuracy of the Single Intradermal Comparative Skin Test for the Diagnosis of Bovine Tuberculosis-Estimated from a Systematic Literature Search

“…To our knowledge only one paper uses a latent class approach in order to estimate sensitivity and specificity of the single intradermal comparative cervical skin test at different cut-offs (for zebu cattle in Chad) [29] and another paper uses a latent class approach to estimate test accuracies of the single intradermal test used in Spain [21]. Different cut-offs for skin thickness used in different countries clearly shows that there is no unambiguous interpretation of the test's results.…”

Isolation and characterization of non tuberculous mycobacteria from humans and animals in Namwala District of Zambia

“…This is in view of the fact that tuberculosis like lesions in wildlife and livestock is highly associated with Mycobacterium bovis [26] and human tuberculosis is also associated with Mycobacterium tuberculosis [27]. This hypothesis is supported by a study done in Chad which suggested that 72% of the tuberculosis lesions in cattle carcasses detected through standard meat inspection were caused by pathogens other than M. bovis [28]. …”