Abstract:
BACKGROUND: Bovine tuberculosis (bTB) is a zoonotic disease with great economic impact estimated at billions of dollars annually worldwide. Meat inspection represents
a long-standing form of disease surveillance that serves both food safety and animal
health. The objective of this study was to determine the prevalence of bTB in livestock at abattoirs using a cell-mediated immune (CMI) assay, the gamma interferon
(IFN-γ) assay. This cross-sectional study was conducted at selected abattoirs (lowthroughput, high-throughput and rural/informal) in Gauteng province, where animals
were also subjected to routine meat inspection.
RESULTS: A total of 410 fresh blood samples were collected from slaughter livestock
(369 cattle and 41 sheep) from 15 abattoirs, and analysed using Bovigam® test kit
with bovine, avian and Fortuitum purified protein derivatives (PPD) as blood stimulating antigens. The estimated prevalence of bTB in cattle was 4.4% (95% CI: 2.4%–
7.3%). The prevalence of bTB in cattle varied between abattoirs (p = .005), ranging
from 0% to 23%; however, there were no significant differences among genders,
breeds, municipality, districts, origins of animals (feedlot, auction or farm) or throughput of abattoirs. The prevalence of avian reactors was 6.0% (95% CI: 3.6%–9.2%) in
cattle, varying between abattoirs (p = .004) and ranging from 0% to 20.7%. None of
the sheep with valid test results was positive for bTB and none was avian reactors
(95% CI: 0%–15%).
CONCLUSION: The detection of bTB reactor cattle in our study clearly shows the limitation of disease surveillance using a meat inspection approach, as all the 410 slaughter
animals sampled had passed visual abattoir inspection and been classified as bTBfree. Our findings therefore emphasize the risk of zoonotic transmission of bTB to
abattoir workers and potential food safety hazard to consumers. Furthermore, our
study highlights the potential for the use of the IFN-γ assay to reduce this risk.
