Comparative evaluation of three commercially available complement fixation test antigens for the diagnosis of glanders.
Authors: Khan I, Wieler L H, Melzer F, Gwida M, Santana V L de A, de Souza M M A, Saqib M, Elschner M C, Neubauer H
Journal: The Veterinary record
Summary
# Editorial Summary: Evaluating Complement Fixation Test Antigens for Glanders Diagnosis Glanders remains a notifiable disease of concern in equine populations, and reliable serological testing is essential for both diagnosis and trade certification. This study compared three commercially available complement fixation test (CFT) antigens—sourced from c.c.pro, the Central Veterinary Institute of Wageningen (CIDC), and the USDA—using 410 sera from affected and unaffected horses, donkeys, mules and laboratory animals, with immunoblotting as the reference standard. The CIDC antigen achieved 100% sensitivity and the USDA antigen 100% specificity, but the USDA antigen's poor sensitivity (62.19%) is a significant limitation; in contrast, the CIDC and c.c.pro antigens showed near-identical performance with >99% sensitivity and 97.5–96.5% specificity respectively, with kappa agreement of 0.96 against the gold standard test. When calculated against the assumed low prevalence of glanders in most non-endemic regions (<0.1%), the CIDC antigen demonstrated optimal negative predictive value (100%), making it the most reliable choice for screening programmes where false negatives pose the greatest risk, whilst the USDA antigen's high specificity but weak sensitivity makes it unsuitable as a primary diagnostic tool. For practitioners involved in export certification, competition clearance, or herd screening, these findings suggest that antigen selection materially affects diagnostic reliability; the CIDC formulation warrants consideration as the preferred option in CFT-based screening protocols.
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Practical Takeaways
- •For glanders diagnosis in endemic regions, CIDC or c.c.pro antigens are superior choices; USDA antigen should be avoided due to poor sensitivity despite perfect specificity
- •When selecting CFT antigens for screening programs, prioritize CIDC (best overall performance) or c.c.pro (marginally lower but still excellent sensitivity with good specificity)
- •In low-prevalence populations, CIDC antigen offers the best balance of sensitivity and specificity for reliable glanders diagnosis and disease exclusion
Key Findings
- •CIDC antigen showed highest sensitivity (100%) followed by c.c.pro (99.39%), while USDA antigen demonstrated substantially lower sensitivity (62.19%)
- •USDA antigen achieved 100% specificity, with CIDC at 97.5% and c.c.pro at 96.5%
- •Almost perfect agreement (κ=0.96) was found between CFT using c.c.pro or CIDC antigens and immunoblotting reference standard
- •At low prevalence (<0.1%), CIDC antigen provided superior positive predictive value (97.04%) and perfect negative predictive value (100%)