Molecular characterization of mycobacterial species isolated from tuberculosis lesions seen in bovine carcasses at post mortem: a case study of three abattoirs in the Accra Region of Ghana.

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October 2010
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Tuberculosis in cattle poses a serious public health threat and yet there is very little information on its extent in Ghana. A study to screen and characterize suspicious carcasses at post-mortem in three selected abattoirs in Accra was conducted. A total of 2,886 cattle slaughtered between June and October, 2009 were examined at post-mortem. One hundred and fifty five (155) suspicious tissue samples were taken from 145 bovines and subjected to Ziehl-Neelsen (ZN) microscopy and subsequently cultured on Löwenstein-Jensen (L-J) media. Isolates were harvested and subjected to ZN microscopy and then screened with the Capilia TB-Neo test and also characterized by a 13-probe Multiplex Ligation-dependent Probe Amplification assay (MLPA). The results revealed an apparent lesion prevalence of 5.0%. ZN microscopy indicated that 32.3% (50/155) of tissues were acid fast. Culture on L-J yielded 85.8% (133/155) isolates. One hundred and twenty-nine out of one hundred and fifty-five (129/155 or 97%) of these were acid fast by ZN microscopy. The Capilia TB-Neo test was performed on 93 of the isolates. Capilia TB-Neo test identified 11.8% (11/ 93) as members of the Mycobacterium tuberculosis Complex (MTBC) and 88.2% (82/93) as Non tuberculous mycobacteria (NTM). A further characterization of isolates using MLPA revealed that 3.8% (5/130) were M. africanum and 6.2% (8/130) were M. bovis. Surprisingly, 38.5 % (50/130) were classified as MTB (not M. bovis or M. africanum). Mixed infection was also identified in 42.9% (3/7) bovines. A comparison of MLPA and Capilia TB-Neo tests using the latter as a “Gold Standard” revealed that MLPA has a sensitivity and specificity of 72.7% and 39.7% respectively. The positive predictive value (PPV) and negative predictive value (NPV) were 16.3% and 90.0% respectively. The data obtained indicates that contamination of beef by TB is prevalent and therefore could pose a serious health threat. More stringent management and control methods should be put in place to improve beef quality.
A Thesis submitted to the Department of Biochemistry and Biotechnology, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Science