First molecular evidence of Brucella abortus circulation in sheep and goats, with comparative evaluation of RBPT and I-ELISA diagnostic performance, in the Mamou region, Republic of Guinea
TL;DR
The combined RBPT and I-ELISA strategy offers a reliable, field-adapted approach for future surveillance of brucellosis in the country and is the first to combine serological and molecular approaches for Brucella surveillance in small ruminants in Guinea.
Abstract
Background: Brucellosis is a neglected zoonosis endemic to sub-Saharan Africa, with poorly documented molecular epidemiology in Guinea. Aim: This study aimed to evaluate the diagnostic performance of two serological tests (Rose Bengal Plate Test [RBPT] and I-enzyme-linked immunosorbent assay [ELISA]) and identify Brucella species circulating in small ruminants using quantitative polymerase chain reaction (qPCR). Methods: A total of 270 serum samples collected from sheep (n = 132) and goats (n = 138) in the Mamou region were tested using the RBPT and I-ELISA. Genomic DNA was extracted from I-ELISA-positive cells and analyzed by qPCR targeting the IS711 gene. Samples with a cycle threshold value ≤35 were considered positive and further analyzed for species identification. Results: The overall seroprevalence was 14.81% (RBPT) and 10.74% (I-ELISA), with no significant difference between the 2 tests (P = 0.197). The seroprevalence was higher in goats (15.94% and 10.87% by RBPT and ELISA, respectively) than in sheep (13.64% and 10.61%), although the differences were not statistically significant (P > 0.05). Using I-ELISA as the reference test, RBPT showed a sensitivity of 96.55%, specificity of 94.61%, positive predictive value of 68.29%, negative predictive value of 99.56%, and area under the curve of 0.9558, reflecting excellent diagnostic concordance between the two tests. However, a false-positive rate of 5.4% was recorded for RBPT. For molecular confirmation, IS711 screening yielded an overall positivity of 55.17%, with 60.00% in goats and 50.00% in sheep. Species identification confirmed Brucella abortus in 81.25% of small ruminants (88.89 % in goats; 71.43 % in sheep). The 3 IS711-positive samples could not be confirmed as either of the targeted species. Abortion was the most strongly associated clinical sign, with 90% of cases confirmed by IS711 polymerase chain reaction and 88.88% identified as B. abortus. Conclusion: To the best of our knowledge, this study is the first to combine serological and molecular approaches for Brucella surveillance in small ruminants in Guinea. The exclusive circulation of B. abortus in the Mamou region. The combined RBPT and I-ELISA strategy offers a reliable, field-adapted approach for future surveillance of brucellosis in the country.