Evaluation of the performance of a rapid enzyme-linked immunosorbent assay in the detection of Anaplasma phagocytophilum antibodies in horses.

This study evaluates the effectiveness of the Snap® 4Dx test, a rapid enzyme-linked immunosorbent assay, in detecting Anaplasma phagocytophilum antibodies in horses. The research concludes that while the Snap® 4Dx test could be a valid method for screening during epidemiological surveys, its use in a clinic setting is not recommended.

Experimental Approach and Findings

• The researchers performed tests on two groups of horses – those that were apparently healthy and asymptomatic (200 in total) and those showing clinical symptoms (244 in total).
• The horses were tested for A. phagocytophilum immunoglobulin G (IgG) antibodies using both the Snap® 4Dx kit and an indirect fluorescence antibody test (IFAT). Here, the IFAT served as the benchmark test.
• Active infection with A. phagocytophilum was assessed in the symptomatic group by analyzing the IFAT IgM titers and conducting a PCR assay to amplify a specific segment of the 16S rRNA gene.
• Out of 45 animals that tested positive for IgG antibodies using IFAT, 40 (89%) were correctly identified through Snap® 4Dx testing. The agreement between the Snap® 4Dx test and the IFAT was found to be very high (k>0.9), indicating that the Snap® 4Dx test performed nearly identically in both symptomatic and asymptomatic animals.

Performance of Snap® 4Dx Against Active Infection

• Roughly 44% (11/25) of Snap® 4Dx positive results in the symptomatic group correlated with an active infection. The remaining 56% (14/25) were either not infected (1/25) or required further testing to confirm infection (13/25). This indicates that the test may not consistently accurately detect active infections.

Conclusions and Implications

• Based on these findings, the Snap® 4Dx test could be an effective screening tool during epidemiological surveys of equine populations. Its rapid results and high level of agreement with the IFAT in detecting IgG antibodies could aid in identifying potential carriers of A. phagocytophilum.
• However, the Snap® 4Dx test’s detection of active infections was found to be inconsistent, limiting its utility in clinical applications. Out of all the Snap® 4Dx positives in symptomatic horses, less than half were associated with active infection.