Tuberculosis or Mycobacterium bovis infection in the African buffalo (Syncerus caffer) and cattle: Immunogenicity and diagnostic value of NTM and MTBC specific mycobacterial antigens.

Abstract

The diagnosis of Mycobacterium bovis infection in the African buffalo (Syncerus caffer), the most important maintenance host of bovine tuberculosis in South Africa, mostly relied on the single intradermal comparative tuberculin test or SICTT. Further ancillary tests have recently become available such as IFN-γ assays and serological tests. In 2011, Michel et al. optimized the IFN-γ assay by introducing PPD-F in concurrence with PPD-A and PPD-B, to improve and broaden diagnostics of BTB in this species. In the current study, the test performance of the following immunoassays was compared: SICTT, BOVIGAM® 1G (B1G), BOVIGAM® 2G (B2G), IDEXX® TB ELISA and an in-house ELISA (IH ELISA). A total of 87 buffaloes in the Hluhluwe-iMfolozi Park (KwaZulu-Natal, South Africa) were subjected to the SICTT in June 2013. Of the 87 buffaloes, 17 animals tested positive, whilst 1 animal was classified as a suspect based on the SICTT. Whole blood samples were taken from these 18 animals and a further 40 randomly selected buffaloes. Post mortem examinations were conducted on the 18 reactors and samples of the lymph nodes of the head and lungs and of lung tissue were taken for bacterial culture at the ARC-OVI. Tuberculous lesions were found in 11 animals upon PM and the culture results are pending. Of the SICTT positive animals, the B1G detected 53% of animals as positive, whereas the B2G detected 77% as positives. Overall results show that the B2G IFN-γ assay using PPD-A and PPD-B as well as the new peptide cocktails (PC-EC & PC-HP) has the highest sensitivity (77.8%), followed by the B2G using only PPD-A & PPD-B (72.2%), the B1G (42.9%), the IDEXX® TB ELISA (34.8%), the B2G using only PC-HP (27.8%), the in-house ELISA (26.1%) and the B2G using only PC-EC (22.2%) in that order. The combination of the SICTT and the B2G IFN-γ assay was found to have the highest sensitivity at 55.6% (in series) or 94.4% (in parallel), whilst the B1G IFN-γ assay was found to have sensitivities of 42.9% (in series) and 81% (in parallel) when combined with the SICTT. When the B1G was combined with the B2G, a sensitivity of 35.3% (in series) and 76.5% (in parallel) was observed. The B2G combined with the IDEXX® TB ELISA had a sensitivity of 22.2% (in series) and 94.4% (in parallel). The B2G and PM together showed a sensitivity of 46.2% (in series) and 84.6% (in parallel). Based on these findings it appears that the B1G can be replaced by the B2G and used concurrently with the SICTT in order to achieve the most accurate diagnosis of bovine tuberculosis in the African buffalo. Furthermore, it may be justifiable not to use the SICTT due to its limitations, as it requires a 72hr boma confinement and two animal darting sessions. The combination of B2G and the IDEXX® TB ELISA or the combination of the B2G and PM could be viable alternatives to such a situation.