Serological Assays of Brucellosis in Unvaccinated Sheep and Goat in Indonesia

Brucellosis is recognized as one of the most widespread zoonotic diseases and is often overlooked, impacting livestock populations worldwide. Annual routine screenings utilize serological assays, such as the Rose Bengal test (RBT) and the complement fixation test (CFT), to identify the presence of brucellosis. The present study aimed to evaluate the diagnostic and discriminative performance of the CFT, the locally produced RBT antigen from Indonesia, the commercial RBT antigen (Pourquier), and the indirect enzyme-linked immunosorbent assay (ELISA) using sera from Indonesian goats and sheep. A total of 184 serum samples were collected, including 92 from goats and 92 from sheep. The samples were obtained through jugular venipuncture from animals on small-scale goat and sheep farms in Java Island, Indonesia. The results were analyzed to determine true prevalence (TP), accuracy, and cross-tabulation with parallel interpretation to assess the sensitivity and specificity of each test analysis. The TP of brucellosis in small ruminant serum samples using local RBT, Pourquier RBT, CFT, and indirect ELISA was 6.99%, 9.74%, 0%, and 14.78% in goats, and 6.92%, 20.34%, 0%, and 7.81% in sheep, respectively. Moderate Kappa interrater reliability was observed between the local and Pourquier RBTs for both goats (0.537) and sheep (0.440). The combined RBT sensitivity in goats and sheep was 27% and 20%, respectively, while the combined RBT specificity was 92% in goats and 80.5% in sheep. Using more than one diagnostic method is essential for screening and investigating brucellosis in goat and sheep populations. A combination of RBT and indirect ELISA tests is recommended to identify Brucella reactors among small ruminants in Indonesia.