Approaches towards optimising the gamma interferon assay for diagnosing Mycobacterium bovis infection in African buffalo (Syncerus caffer)

Abstract

Please cite this article in press as: Michel, A.L., et al., Approaches towards optimising the gamma interferon assay for diagnosing Mycobacterium bovis infection in African buffalo (Syncerus caffer). PREVET (2010) b s t r a c tThe application of diagnostic tests for bovine tuberculosis in wildlife poses formidable technical difficulties and the use of the gamma interferon assay offers a simplified approach to testing wild animal species. We compared the performance of the gamma interferon assay in African buffalo (Syncerus caffer) under the recommended guidelines for interpretation of test results and found a high sensitivity (92.1%) at the cost of a greatly reduced specificity (68.3%). The optimised cut-off value for positive test results under local conditions was identified at an optical density of 0.385 at wavelength 450 nm as the preferred compromise between sensitivity and specificity. Additional optimisation approaches to improve test performance were examined and showed that the application of 'a priori exclusions' of test results on the basis of reactivity to fortuitum PPD (sensitin produced from Mycobacterium fortuitum) and to a lesser degree, avian PPD, increased specificity without losing sensitivity. The implications of these findings on a modified testing protocol adjusted to include measurement of immune responsiveness to fortuitum PPD and other interpretation schemes are discussed.

Enemies and turncoats: bovine tuberculosis exposes pathogenic potential of Rift Valley fever virus in a common host, African buffalo ( Syncerus caffer )

“…In brief, this assay is performed by comparing the in vitro IFNg response to M. bovis antigen (bovine tuberculin) with the IFNg response to an avian tuberculin antigen and background IFNg levels in the absence of antigenic stimulation. This assay has been optimized for use in African buffalo [47], and blood cells from buffalo infected with M. bovis show a pronounced spike in IFNg production in response to bovine but not avian tuberculin, whereas bovine tuberculin challenge does not induce IFNg production in the blood of unexposed animals [47]. We implemented the gamma interferon assay with the BOVIGAM enzyme-linked immunosorbent assay kit (Prionics), which has a sensitivity of 86% and a specificity of 92% in African buffalo [47].…”

“…This assay has been optimized for use in African buffalo [47], and blood cells from buffalo infected with M. bovis show a pronounced spike in IFNg production in response to bovine but not avian tuberculin, whereas bovine tuberculin challenge does not induce IFNg production in the blood of unexposed animals [47]. We implemented the gamma interferon assay with the BOVIGAM enzyme-linked immunosorbent assay kit (Prionics), which has a sensitivity of 86% and a specificity of 92% in African buffalo [47]. We used the BOVIGAM test instead of the skin test used at the buffalo breeding facility because the skin test was impractical in our field setting; the skin test requires two captures in 3 days, whereas the BOVIGAM test can be performed on whole blood collected in one capture.…”

TUBERCULOSIS AND BRUCELLOSIS IN WOOD BISON (BISON BISON ATHABASCAE) IN NORTHERN CANADA: A RENEWED NEED TO DEVELOP OPTIONS FOR FUTURE MANAGEMENT

“…Several serologic tests for bTB, including the Cervid TB StatPak TM (Chembio Diagnostics Ltd, Medford, New York, USA), EnferPlex TB Assay TM (Enfer Group, Kildare, Ireland), and IDEXX TB Assay TM (IDEXX Laboratories, Westbrook, Maine, USA), were developed for cattle and cervids (Lyashchenko et al 2000;Whelan et al 2008Whelan et al , 2010O'Brien et al 2009;Buddle et al 2010;Schiller et al 2010;Clegg et al 2011), but few, if any, are validated for bison. c-Interferon assays also have broad utility in cattle testing, but little work has been performed in bison (Schiller et al 2010), although these tests were useful in African buffalo (Syncerus caffer; Michel et al 2011). Combinations of cell-mediated tests and serologic tests offer optimal sensitivity for diagnosis of bTB in most wildlife species (Lyashchenko et al 2008;Buddle et al 2009Buddle et al , 2010Chambers et al 2009;Drewe et al 2009), and that may apply to bison as well.…”

Facts and dilemmas in diagnosis of tuberculosis in wildlife

“…On a daily basis, wildlife species are tested for BTB for various purposes, often with diagnostic assays that are accepted due to a lack of a better alternative [37]. However, because of the recognition of the role of particular wildlife species like badgers, possums and white-tailed deer in the maintenance of the M. bovis infection, as well as its spillover into additional species, an increasing number of studies has been dedicated to the development of diagnostic assays for specific wildlife species, resulting in assay prototypes and partially or fully validated assays [38][39][40][41].…”