Modeling foot-and-mouth disease dissemination in Brazil and evaluating the effectiveness of control measures

Abstract

Foot-and-mouth disease (FMD) infects multiple food-animal species, thus capable of disseminating among ungulate species with distinct transmission rates. Here present a multilevel compartmental stochastic model, taking into account births and deaths and explicit representation of species-specific transmission dynamics. The model considered two major modes of dissemination, between-farm animal and spatial transmission. Our model outcomes are the number of secondary infected animals and farms, spatial dissemination distances, and effectiveness of depopulation and vaccination along with surveillance and movement restrictions. We demonstrated that after 20 days of FMD dissemination, the median number of infected farms was 8 (IQR: 3-22), of which 7 (IQR: 3-22) were bovine, 3 (IQR: 1-6) swine farms, and 1 (IQR: 1-1) small ruminants. We demonstrate that animal movement dominated dissemination in the first days of epidemics, while at ten days the spatial transmission dominated bovine infections, whilst between-farm led to most swine infections. We have also shown the median distances between seeded and secondary infections was 5.77 km (IQR: 1-10.29 km), with some long-range dissemination at 695.40 km. We estimated that depopulating 12 and vaccinating 15,000 farms per day faded out 98.3% of the epidemics, however, was insufficient to contain large-scale epidemics (> 248 infected farms). The estimated effectiveness of a baseline control scenario eliminated 93.4% of the epidemics with a median of 9 (IQR: 3-23, max: 221) infected farms. Our results demonstrated that the depopulation alone against epidemics with more than 74 infected farms had limited success, stamping out less than 80% of simulations. The developed transmission model allows for cross-species transmission to be considered in FMD policy-making, and the software implementation facilitates the adaption of scientific-based support to FMD planning and response throughout other Brazilian states.