Modeled impacts of rapid and accurate cattle tracing in a Foot-and-Mouth Disease outbreak in the US

Abstract

The purpose of this study was to estimate the impacts of rapid and accurate tracing of cattle movements during a Foot-and-Mouth Disease (FMD) outbreak in the United States (US). To simulate introduction and spread of FMD we utilized InterSpread Plus, a spatially explicit disease transmission model, and a national livestock population file. The simulations began in one of four regions of the US via beef or dairy cattle as the index infected premises (IP). The first IP was detected 8, 14, or 21 days after introduction. The tracing levels were defined by the probability of a successful trace and the time to trace completion. We evaluated three tracing performance levels, a baseline that represents a mix of paper and electronic interstate shipment records, an estimated partial implementation of electronic identification (EID) tracing, and an estimated full implementation of EID tracing. To evaluate the potential to decrease the size of control areas and surveillance zones with full EID use, we compared the standard size for each to a reduced geographical area for each. The total number of IPs in an outbreak varied with the location of the index farms. Within index farm locations and across tracing performance levels, early detection (day 8) resulted in fewer IPs and a shorter duration of the outbreak. The impact of improving tracing was most evident within introduction region when detection was delayed (day 14 or 21). Full EID use decreased the 95th percentile but had a smaller impact on the median number of IPs. Improved tracing also decreased the number of farms impacted by control efforts in control areas (0–10 km) and surveillance zones (10–20 km) by decreasing outbreak size (total IPs). Decreasing the control area (0–7 km) and surveillance zone (7–14 km) sizes while using full EID tracing further decreased the number of farms under surveillance but increased the number of IPs slightly. Consistent with previous results, this supports the potential value of early detection and improved traceability to control FMD outbreaks. Further development of the EID system in the US is necessary to achieve the modeled results. Further research into the economic impacts of enhanced tracing and decreased zone sizes are needed to determine the full impact of these results.