Comparative evaluation of competitive and indirect ELISA kits for detection of bluetongue virus antibodies in ovine sera from an endemic region

Bluetongue virus (BTV) remains an important pathogen of small ruminants in endemic regions, necessitating reliable serological tools for surveillance and diagnosis. This study evaluated the diagnostic performance of a newly developed indirect ELISA kit (LT-Biotech), based on a plant-derived recombinant VP7 antigen, in comparison with a commercial competitive ELISA (ID Screen® Bluetongue Competition, ID-Vet). A total of 56 ovine serum samples collected in a blue tongue-endemic region of the Middle East were tested in parallel using both assays.
Using an optimized cut-off value of OD = 0.5, the indirect ELISA demonstrated a diagnostic sensitivity of 90% and a specificity of 94% relative to the competitive ELISA. The positive and negative predictive values were 97% and 79%, respectively. The likelihood ratios (LR+ = 14.4; LR− = 0.11) indicated strong discriminative power, and the overall agreement between the two assays reached 91%, with a Cohen’s kappa coefficient of 0.79, reflecting substantial concordance.
These findings show that the plant-derived VP7 indirect ELISA provides a balanced diagnostic profile and performs comparably to the commercial competitive ELISA. The assay represents a promising tool for routine serological screening and epidemiological monitoring of bluetongue in small ruminant.