Seroprevalence and Genetic Resistance of Dairy Cattle To Brucellosis in Smallholder Dairy Farming System In Selected Regions of Tanzania
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Date
2025-01
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NM-AIST
Abstract
Brucellosis in livestock is caused by different species such as B. abortus (cattle), B. melitensis (goats), B. ovis (sheep), B. suis (pigs) and B. canis (dogs). Recent studies in different regions have reported an increasing trend in smallholder dairy cattle. Furthermore, neighboring countries have reported identification of B. melitensis in dairy cattle, this is not known in Tanzania. In addition, the use of brucellosis resistant cattle has shown promising impact in controlling the disease in other countries, however it is not known if Tanzanian dairy cattle population contains genetic markers which are associated with the resistance/susceptibility to brucellosis. To address these questions, a cross-sectional study design was conducted in two agroecological zones, the Northern zone (Arusha, Kilimanjaro and Tanga regions) and the Southern highland zone (Iringa, Njombe and Mbeya regions) to determine brucellosis seroprevalence, risk factors, Brucella species circulating in smallholder dairy cattle farming
systems and conduct Genome-wide association studies on cattle genome to identify SNP markers associated with brucellosis resistance/susceptibility. Seroprevalence was calculated at different administrative scales, and spatial tests were used to detect disease hotspots. A generalized mixed-effects regression model was built to explore the relationships among Brucella serostatus, animals and farm management factors. The overall seroprevalence was 2.39% (49/2048 cattle, 95% CI 1.7-3.1) across the study area and the Njombe Region represented the highest percentage with 15.5% (95% CI 11.0-22.0). In addition, hotspots were detected in the Njombe and Kilimanjaro Regions. Mixed-effects regression models showed that having goats around (OR 3.02, 95% CI 1.22-7.46) and abortion history (OR 4.91, 95% CI 1.43-16.9) were significant risk factors for brucellosis. The GEMMA analysis results identified a SNP marker BovineHD0900011750 located in chromosome number 9 responsible for brucellosis susceptibility (odds ratio >1) in 5.6% of the 1977 study animals. The web-based Ensembl variant effect predictor showed that the marker is found in a protein-coding region called ATPase Family Gene 1 homology (AFG1L) which produces mitochondrial integral membrane protein responsible for mitochondrial protein homeostasis and its impact in gene expression has been categorized as modifier as the direction of the impact is not yet known.
Education of dairy farmers about brucellosis and its control, particularly in relation to goats in this setting is advised. In addition, a One-Health approach is needed to further study the role of small ruminants in dairy cattle brucellosis and the status of brucellosis in dairy farmers in the Njombe and Kilimanjaro Regions.
Sustainable Development Goals
SDG: 2- Zero Hunger
SDG: 3- Good Health and Well-Being