Application of the gamma-interferon assay to determine the prevalence of bovine tuberculosis in slaughter livestock at abattoirs in Gauteng, South Africa.

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 (low-throughput, 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 bTB-free. 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.

Validation of an ELISA for the concurrent detection of total antibodies (IgM and IgG) to Rift Valley fever virus.

Rift Valley fever virus (RVFV) infects humans and livestock, causing haemorrhaging and abortions in animals. Three major RVF epizootics have occurred in South Africa since the 1950s and the outbreak in 2010 had a mortality rate of 10.7% in humans. Accurate and early detection is therefore essential for management of this zoonotic disease. Enzyme-linked immunosorbent assays (ELISAs) have been developed for the detection of either IgM or IgG antibodies to RVFV in animal sera. In this study, data are presented on the validation of a double-antigen ELISA for the simultaneous detection of both classes of antibodies to RVFV ina single test. ELISA plates were coated with a recombinant nucleoprotein. The nucleoprotein,conjugated to horseradish peroxidase, was used as the detecting reagent. A total of 534 sera from sheep and cattle were used in the validation. The sheep sera were collected during a RVF pathogenesis study at the Agricultural Research Council (ARC) - Onderstepoort Veterinary Institute and the cattle sera were collected during an outbreak of RVF in 2008 at the ARC -Animal Production Institute in Irene, Pretoria. The ELISA had a diagnostic sensitivity of 98.4% and a specificity of 100% when compared to a commercial cELISA. This convenient and fast assay is suitable for use in serological surveys or monitoring immune responses in vaccinated animals.