Effect of incubation temperature on the diagnostic sensitivity of the glanders complement fixation test.

This study reviews the sensitivity and accuracy of the Glanders Complement Fixation Test (CFT), used to identify the glanders disease in equines during international trading. By comparing two test processes – one warm (37°C for 1 hour) and one cold (overnight at 4°C), it identified that the cold test is more reliable in detecting the disease, though it is associated with lower diagnostic specificity.

Introduction to Glanders and the CFT testing methods

• Glanders is a disease among equines (horses, donkeys, and mules) that needs to be identified before they are involved in international trading. The World Organisation for Animal Health (OIE) uses the Complement Fixation Test (CFT) for this purpose.
• The CFT, however, faced criticism in the past due to erroneous results – both false positives and negatives have previously caused financial losses and inadvertent introduction of the disease to previously glanders-free areas.
• The CFT can be performed under two conditions – warm (incubation at 37°C for 1 hour) and cold (overnight incubation at 4°C), and both are recommended by OIE.

Comparing the two testing methods

• The objective of this research was to compare the sensitivity and specificity of the warm and cold CFT techniques. Using the antigen provided by the United States Department of Agriculture, the study aimed to determine which CFT technique offers more reliable results.
• The study found that the warm CFT was significantly less sensitive as compared to the cold CFT – 56.8% vs 83.6% (p < 0.0005). Here, sensitivity refers to the ability of a test to identify positive results.
• However, the cold CFT is associated with lower diagnostic specificity. This means that while it is more likely to correctly identify positive cases, it may also produce more false positives.
• The immunoblot was used as the gold standard in this test – it is a widely accepted high-standard method in identifying organisms/infections/diseases.

Conclusion

• Implementing the cold CFT increases the detection rate of glanders in equines being traded internationally, but at the cost of lower diagnostic specificity, increasing the rate of false positives.
• The findings of this research may guide updates and improvements to the CFT and other diagnostic methods to ensure safer and more reliable international equine trade.