Phenotypic and genotypic characterization of Brucella strains isolated from autochthonous livestock reveals the dominance of B. abortus biovar 3a in Nigeria

Brucellosis is a worldwide widespread zoonosis caused by bacteria of the genus Brucella. Control of this disease in a given area requires an understanding of the Brucella species circulating in livestock and humans. However, because of the difficulties intrinsic to Brucella isolation and typing, such data are scarce for resource-poor areas. The paucity of bacteriological data and the consequent imperfect epidemiological picture are particularly critical for Sahelian and Sub-Sahara African countries. Here, we report on the characterization of 34 isolates collected between 1976 and 2012 from cattle, sheep and horses in Nigeria. All isolates were identified as Brucella abortus by Bruce-ladder PCR and assigned to biovar 3 by conventional typing. Further analysis by enhanced AMOS-ERY PCR showed that all of them belonged to the 3a sub-biovar, and MLVA analysis grouped them in a cluster clearly distinct from that formed by European B. abortus biovar 3b strains. Nevertheless, MLVA detected heterogeneity within the Nigerian biovar 3a strains. The close genetic profiles of the isolates from cattle, sheep and horses, suggest that, at least in some parts of Nigeria, biovar 3a circulates among animal species that are not the preferential hosts of B. abortus. Consistent with previous genetic analyses of 7 strains from Ivory Cost, Gambia and Togo, the analysis of these 34 Nigerian strains supports the hypothesis that the B. abortus biovar 3a lineage is dominant in West African countries.