Comparative Evaluation of RBPT, I-ELISA, and CFT for the Diagnosis of Brucellosis and PCR Detection of Brucella species from Ethiopian Sheep, Goats, and Cattle sera

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Abstract Method: Brucella is an intracellular bacterium that affects both animals and humans. The aim of this study was to compare brucellosis diagnostic methods such as RBPT, I-ELISA, CFT and PCR detection of Brucella species. A total of (552) Sheep, (1345) Goats, and (420) Cattle sera samples were collected with no history of vaccination from brucellosis reported regions of Ethiopia. All sera samples were subjected to comparative serological assays. Post- cross tabulation, sensitivity and specificity were determined using Receiver Operating Characteristics (ROC) curve analyses software. Fifty-four sero-positive sera samples were also subjected to PCR amplification targeting Brucella Genus-specific, as well as B. abortus, and B. melitensis species specific primers. Results: Among 2317 sera samples subjected to comparative serological diagnostic tests (RBPT, I-ELISA and CFT), 189 (8.16 %) for RBPT, 191 (8.24 %) for I-ELISA and 48 (2.07 %) on CFT were found to be positive. Sensitivity on RBPT was 100 % with (95%) in Sheep, 100% (95%) Goats and 74% (95%) Cattle. Specificity on RBT was 98.69% (95%), 99.28% (95%), 100 (95%) in Sheep, Goats and Cattle, respectively. Sensitivity on CFT was 4% with (95) in Sheep 9.65 (95%) Goats and 72 (95%) Cattle. Specificity on CFT was 100 % (95%) for each Sheep, Goats and Cattle. In PCR amplified product analyses, a 223bp in Brucella genus-specific and 156bp B.abortus species specific were detected from all study animals. However, B. melitensis was not detected in all sera samples. Conclusion: In this study Indirect-ELISA was found to be the most sensitive and specific test. RBPT was also sensitive enough to detect all Brucellosis-infected Sheep and Goats. However, this test showed false positive in Sheep and Goats and false negative results in cattle. Therefore, RBT should be complemented with ELISA to solve problems associated with sensitivity and specificity of RBT. PCR assay employed in this study confirmed the presence of B. abortus in small and large ruminants consistent to the study sites. This study is the first report on the detection of B.abortus on small ruminants’ serum in Ethiopia. We could detect B. abortus in non-preferred hosts. The findings suggest further extensive works are required to determine the genetic diversity of Brucella species and understand their molecular epidemiology at national level to design cost effective prevention and control methods.

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