High-Specificity Test Algorithm for Bovine Tuberculosis Diagnosis in African Buffalo (Syncerus caffer) Herds

Area of Science:

• Veterinary Immunology
• Infectious Disease Diagnostics
• Wildlife Health

Background:

• Ante-mortem bovine tuberculosis (bTB) diagnostics for buffaloes include SCITT, IGRA, and IPRA.
• Existing parallel testing algorithms may lack specificity for screening bTB-free buffalo herds.
• High specificity is crucial to avoid false positives in historically negative populations.

Purpose of the Study:

• Determine the specificity of SCITT, IGRA, and IPRA in M. bovis-unexposed buffaloes.
• Develop a high-specificity diagnostic algorithm for bTB screening in buffaloes.
• Investigate potential cross-reactivity of cytokine assays with nontuberculous mycobacteria (NTM).

Main Methods:

• Specificity determination using M. bovis-unexposed, historically negative herds.
• Evaluation of serial (positive on both IGRA and IPRA) versus parallel testing.
• Assessment of cytokine assay results against NTM presence in oronasal swabs.
• Application of serial testing in a historically bTB-free herd (n=153).

Main Results:

• Serial IGRA and IPRA testing achieved 98.3% specificity, significantly higher than individual tests or parallel testing (73%).
• Adding SCITT to the serial algorithm resulted in 100% specificity.
• No association was found between NTM presence and positive cytokine assay results.
• In a bTB-free herd, serial IGRA/IPRA identified four buffaloes with confirmed M. bovis infection.

Conclusions:

• Serial interpretation of IGRA and IPRA provides a highly specific screening method for buffaloes in historically bTB-free herds.
• This approach enhances the detection of M. bovis-infected animals while minimizing false positives.
• The findings support the use of IGRA and IPRA in series for effective bTB surveillance in susceptible buffalo populations.