Bovine brucellosis and worker health in Minas Gerais: SIR modeling and occupational risk estimation

Abstract

Bovine brucellosis is an endemic zoonosis in Brazil with a direct impact on the health of rural and agro-industrial workers. This study aims to model the transmission dynamics of bovine brucellosis in Minas Gerais and estimate the associated human occupational risk. Secondary data from the Brazilian Institute of Geography and Statistics, the Minas Gerais Institute of Agriculture and Livestock, and the Notifiable Diseases Information System, referring to 2023, were used. Transmission within the herd was simulated using a compartmental SIR (Susceptible–Infected–Removed) model, calibrated with parameters from recent national literature (β = 1.5 × 10⁻⁷ day⁻¹; γ = 0.04 day⁻¹). A proportional equation was applied to estimate the probability of human infection under different levels of occupational exposure. With a vaccination coverage of 77.5% and an estimated population of approximately 5.06 million susceptible cattle, the model indicated a high basic reproduction number (R₀ ≈ 19) and a maximum prevalence of infected animals of 17.8% at the peak of the epidemic curve (day 26), revealing that current vaccination coverage is far below the theoretical threshold required to prevent the circulation of the agent within the herd (≈ 98.8%). The probability of human infection estimated by the proportional model was on the order of 10⁻⁹ in the occupational exposure scenarios evaluated, a value that contrasts sharply with empirical findings from the literature — which describe odds ratios of up to 3.47 among exposed workers and seroprevalence rates of up to 6.9% in high-risk occupational populations — indicating that the simplified proportional model tends to substantially underestimate the actual risk. SIR modeling is a useful tool for supporting public health decision-making, but its application to human risk estimation must be interpreted with caution and always triangulated with active serological surveillance, especially in light of the Clinical Protocol and Therapeutic Guidelines for Human Brucellosis, which reinforces the One Health approach in linking animal health, worker health, and epidemiological surveillance in Minas Gerais.