Bovine Brucellosis in Dairy Herds in Mali and Niger, 2024: Apparent Seroprevalence and Epidemiological Factors.

As part of the PRISMA project, which promotes research and innovation for productive, resilient, and healthy agro-pastoral systems in West Africa, a cross-sectional survey was conducted to assess the apparent seroprevalence and investigate epidemiological factors associated with bovine brucellosis in dairy herds. The survey was carried out in Mali (Bamako, Koulikoro, Mopti, and Sikasso regions) and Niger (Tahoua, Dosso, and Tillabéry regions). A total of 1230 animals from 82 herds were tested, including 645 animals from 43 herds in Mali and 585 animals from 39 herds in Niger. At the herd level, apparent seroprevalence was significantly higher in Mali than in Niger (37.21% vs. 15.38%). Within each country, animal-level seroprevalence varied across region, with the highest levels observed in Bamako (11.11%) and Mopti (7.62%) in Mali, and Dosso (6.67%) in Niger. High within-herd prevalence (>20%) was identified in only one herd per country. The higher overall herd-level seroprevalence in Mali was primarily driven by a greater number of herds with low (≤10%) within-herd seroprevalence. Univariate risk factor analysis at the animal level identified a borderline trend toward higher odds of seropositivity in crossbred cattle than other breeds (OR = 1.95, 95% CI: 1.00-3.81, p = 0.0503). In addition, a classification tree analysis highlighted seven exploratory signals of the positive herd status. These included four animal/management-level factors-herd region, environmental disposal of aborted placentas, the number of lactating cows (as a proxy for animal density), and reported herd abortions-as well as three human-level signals within the household: a history of miscarriage, experiencing heavy night sweats, and suffering from undulant fever. In conclusion, this survey provides new insights into bovine brucellosis and its epidemiology in dairy herds in Mali and Niger, confirming established high-prevalence areas such as Bamako and identifying new zones of concern, such as Mopti and Dosso. Our findings underscore that bovine brucellosis remains an important public health and economic threat in both countries. Given that the identified positive regions are hubs for milk production and consumption, these data may support health authorities in implementing targeted surveillance, control, and prevention strategies under a One Health approach.