Seroepidemiological Investigation of Bovine Brucellosis in the Extensive Cattle Production System of Tigray Region of Ethiopia

A cross-sectional epidemiological study was carried out from September 2004 to March 2005 to determine the seroprevalence and identify risk factors for seropositivity of bovine brucellosis in the extensive cattle production systems of Tigray Region. The study populations comprised indigenous breed cattle in the region, and samples were selected by 2-stage cluster sampling. Serum samples collected from 816 extensively managed cattle herds above 6 months of age were screened for Brucella antibodies by the Rose Bengal Plate Test and reactor sera were further tested by the Complement Fixation Test (CFT). Moreover, information was gathered on individual animal and farm-level risk factors and other farm characteristics using a questionnaire. In this study, the overall seroprevalence of Brucella antibodies in the extensively managed cattle was 3.19% based on CFT. The overall herd-level prevalence was 42.31% and the within-herd prevalence varies from 0% to 15.15% based on CFT. The results of univariate logistic regression analysis revealed that seropositivity to brucellosis was significantly higher in animals kept under the transhumance management system than animals in the sedentary system (P < 0.001). The results also indicated that there was a statistically significant increase in seroprevalence to brucellosis with increasing age (P < 0.01) but not parity (P > 0.05). Significant increment of seropositivity was also observed as herd size increases from small to medium (P < 0.05) and then to large sizes (P < 0.001). In addition, a significantly higher seroprevalence was found in animals in the lowland than those in the highland agro-climatic zones. Nevertheless, in the multivariate logistic regression analysis, systemic factor (odds ratio [OR] = 10.6%, 95% confidence interval [CI] = 2.3-49.3, P < 0.01) and age (OR = 4.2, 95% CI = 2.3-49.3, P < 0.01) were identified as the major risk factors for individual animal seroprevalence. Furthermore, Fisher’s Exact Test revealed that seropositivity to brucellosis had statistically significant association with history of previous abortions and stillbirths. The results of this study showed that brucellosis is an endemic and widely distributed disease