Animal Movements and FMDV Transmission during the High-Risk Period of the 2001 FMD Epidemic in Uruguay

Samenvatting

During the 2001 foot-and-mouth disease (FMD) epidemic in Uruguay, many farms were already infected and foot-and-mouth disease virus (FMDV) had spread throughout the country by the time the first outbreak was detected and a ban on animal movements was implemented. Before this ban, movements of infected animals between livestock premises were probably one of the main factors contributing to the spread of the disease. Understanding and quantifying this contribution allow identifying risk premises or risk areas to help policymakers to implement effective interventions and enhance targeted surveillance. The aim of this study was to describe, visualize, and analyze the network of livestock movements between livestock premises during the initial phase of the 2001 FMD epidemic in Uruguay and gain insight into the risk of transmission by estimating the between herd basic reproduction number (RH) before a ban on animal movements was implemented. Here, we derived RH from the average number of outcontacts of infected premises and the average probability that a contact leads to infection. Additionally, we analyzed the current (2022) network of livestock movements in Uruguay, for the same period as in 2001, and estimated RH assuming the same probability of infection as in 2001. We found that the movements of infected animals during the high-risk period of this epidemic—i.e., the period between FMDV introduction and the detection of the index case—had an important contribution to the virus spread among premises (RH = 1.48). Livestock markets and highly connected farms were responsible for the early long-distance spread of FMDV. The analysis of the 2022 network shows that this network is similar to that of 2001 and highlights the importance of targeting highly connected premises, particularly livestock markets, for surveillance, target early detection, and implement interventions during epidemics.