Parameter estimation and use of gamma interferon assay for the diagnosis of bovine tuberculosis in Brazil

Lopes L. B., Alves T. M., Stynen A. P. R., Mota P. M. P. C., Leite R. C. & Lage A. P. 2012. Parameter estimation and use of gamma interferon assay for the diagnosis of bovine tuberculosis in Brazil. Pesquisa Veterinaria Brasileira 32(4): 279-283. Embrapa Agrossilvipastoril, Rodovia MT 222, km 2,5, Caixa Postal 343, Sinop, MT 78.550-970, Brazil. E-mail: luciano.lopes@embrapa.br This study aimed to evaluate the interference of tuberculin test on the gamma-interferon (INF gamma) assay, to estimate the sensitivity and specificity of the INF gamma assay in Brazilian conditions, and to simulate multiple testing using the comparative tuberculin test and the INF gamma assay. Three hundred-fifty cattle from two TB-free and two TB-infected herds were submitted to the comparative tuberculin test and the INF gamma assay. The comparative tuberculin test was performed using avian and bovine PPD. The INF gamma assay was performed by the Bovigam (TM) kit (CSL Veterinary, Australia), according to the manufacturer's specifications. Sensitivity and specificity of the INF gamma assay were assessed by a Bayesian latent class model. These diagnostic parameters were also estimate for multiple testing. The results of INF gamma assay on D0 and D3 after the comparative tuberculin test were compared by the McNemar's test and kappa statistics. Results of mean optical density from INF gamma assay on both days were similar. Sensitivity and specificity of the INF gamma assay showed results varying (95% confidence intervals) from 72 to 100% and 74 to 100% respectively. Sensitivity of parallel testing was over 97.5%, while specificity of serial testing was over 99.7%. The INF gamma assay proved to be a very useful diagnostic method.