This study investigates brucellosis transmission among humans and ruminants, together with environmental contamination, using the original nine-compartment deterministic model. The analysis examines solution properties, the disease-free and endemic equilibria, the basic reproduction number and the direction of the threshold bifurcation. For the system as formulated, the next-generation method gives a reproduction threshold that is consistent with the endemic-equilibrium existence condition: a unique positive equilibrium exists when R₀ exceeds one. A centre-manifold calculation verifies the coefficients at the critical threshold and gives a forward bifurcation. The numerical illustrations study depict the ruminant and human compartments and environmental bacterial dynamics, emphasising the relevance of ruminants and environmental exposure in brucellosis transmission. The model and results inform consideration of transmission reduction, treatment and environmental contamination control over time. Read more