Non-agreement between 2 serologic techniques for detecting antibody to Brucella ovis in naturally infected sheep

Brucella ovis is the causative agent of ovine brucellosis, which is an important infectious disease in sheep farming worldwide and is responsible for economic losses because of its negative effect on the reproductive system of rams and ewes. Serologic tests are the main tools for detection of infection; however, these tests commonly yield a high frequency of false-negative results. We compared 2 serologic tests, agar gel immunodiffusion (AGID) and ELISA, for the detection of anti-B. ovis antibodies in naturally infected sheep. Of the 728 serum samples analyzed, 0.3% were positive by AGID and 9.2% by ELISA. Positive results were obtained for different animals and flocks. There was no statistical difference between the detection frequency of the 2 methods (p = 0.674), and the kappa test indicated low concordance (κ = 0.005). The lack of agreement between results obtained using AGID and ELISA, associated with the absence of clinical signs, makes it difficult to detect ovine brucellosis efficiently, and demonstrates the need for effective tests for the definitive detection of B. ovis infection.